Characteristics and Petrogenesis 

of Alaskan^Type «/ J:

Ultranaafic-Mafic Intrusions, 

Southeastern Alaska

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Characteristics and Petrogenesis 

of Alaskan-Type 

Ultramafic-Mafic Intrusions, 

Southeastern Alaska

By Glen R. Himmelberg and Robert A. Loney

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1564

Field relations, petrography, rock chemistry, mineral chemistry,

and interpretation of origin and emplacement of Alaskan-type intrusions

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

For sale by

U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

Text and illustrations edited by Mary Lou Callas

Graphics by authors 

Layout by Mary Lou Callas

Library of Congress Cataloging-in-Publication Data

Himmelberg, Glen R.

Characteristics and petrogenesis of Alaskan-type ultramafic-maflc intrusions, southeastern Alaska / by Glen R. 

Himmelberg and Robert A. Loney.

p. cm. — (U.S. Geological Survey professional paper : 1564)

"Field relations, petrography, rock chemistry, mineral chemistry, and interpretation of origin and emplacement of 

Alaskan-type intrusions."

Includes bibliographical references (p. - ). 

Supt. of Docs, no.: 119.16:1564

1. Intrusions (Geology)—Alaska. 2. Rocks, Ultrabasic—Alaska. 3. Geochemistry—Alaska. I. Loney, Robert Ahlberg, 

1922- . II. Title. III. Series. 

QE611.5.U6H56 1995

551.8'8'097982-«ic20 95-2236

CIP
CONTENTS

Abstract ———————————————————————————————————————————— 1

Introduction —————————————————————————————————————————— 2

Regional setting and age——————————————————————————————————— 3

Field relations and petrography ——————————————————————————————— 3

Relation of Alaskan-type ultramafic intrusions to regional structure and metamorphism— 8

General statement ———————————————————————————————————— 8

Union Bay complex ——————————————————————————————————— 9

Kane Peak complex ——————————————————————————————————— 11

Blashke Islands complex ———————————————————————————————— 15

Rock chemistry ————————————————————————————————————————— 17

Major elements ————————————————————————————————————— 17

Trace elements —————————————————————————————————————— 19

Mineral chemistry —————————————————————————————————————— 26

Discussion —————————————————————————————————————————— 33

Crystallization conditions of ultramafic-mafie rocks ————————————————— 33

Nature of the parent magma —————————————————————————————— 39

Intrusive mechanism and zonal structure—————————————————————————— 41

Conclusions ————————————————————————————————————————— 42

References cited ——————————————————————————————————————— 43

FIGURES

1. Map of southeastern Alaska showing locations of Alaskan-type ultramafic-mafic intrusions and major

tectonostratigraphic units——————————————————————————————————————————— 4

2. Geologic map of ultramafic complex at Red Bluff Bay ————————————————————————— 7

3. Geologic map of ultramafic complex at Union Bay ——————————————————————————— 10

4. Hypothetical cross section through ultramafic complex at Union Bay —————————————————— 11

5. Equal-area lower hemisphere plots of structural data in Union Bay area ———————————————— 12

6. Equal-area lower hemisphere plots of olivine X, Y, and Z axes in ultramafic complex at Union Bay -- 13

7. Geologic map of ultramafic complex at Kane Peak ——————————————————————————— ^

8. Equal-area lower hemisphere plots of structural data in metaturbidites in Kane Peak area —————— 15

9. Equal-area lower hemisphere plots of olivine X, Y, and Z axes in ultramafic complex in Kane Peak

area————————————————————————————————————————————————————— 16

10. Geologic map of ultramafic complex at Blashke Islands ————————————————————————— 18

11. Equal-area lower hemisphere plots of olivine X, Y, and Z axes in ultramafic complex at Blashke

Islands ——————————————————————————————————————————————————— ^

12. Rare-earth element patterns of ultramafic and gabbroic rocks of Alaskan-type intrusions at Blashke

Islands, Kane Peak, Union Bay, Salt Chuck, and Port Snettisham ——————————————————— 22

13. Rare-earth element patterns of ultramafic xenoliths, plutonic gabbros, and a tholeiite flow associated

with Aleutian island-arc volcanism ————————————————————————————————————— 23

III
IV CONTENTS

14-18. Plots of chemical parameters of Alaskan-type intrusions:

14. Compositions of clinopyroxene and orthopyroxene in ultramafic rocks and gabbro ————————— 28

15. Weight percent A12O3 against Mg/(Mg+Fe2+) of clinopyroxene in ultramafic rocks and gabbro —— 29

16. Percent A1IV against weight percent TiO2 for clinopyroxene in clinopyroxenite and gabbro ———— 29

17. A1IV against cations in A-site for hornblende in ultramafic rocks and gabbro ———————————— 33

18. Cr/(Cr+Al+Fe3+) against Fe2+/(Mg+Fe2+) for chromian spinel in ultramafic rocks —————————— 33

TABLES

1. Major rock types and characteristics of Alaskan-type ultramafic-mafic bodies............................................ 6

2. Chemical compositions of Alaskan-type ultramafic and mafic rocks ........................................................... 20

3. Trace-element contents of Alaskan-type ultramafic and mafic rocks............................................................ 24

4-9. Analyses of minerals in Alaskan-type ultramafic and mafic rocks:

4. Olivine................................................................................................................................................... 27

5. Orthopyroxene...................................................................................................................................... 28

6. Clinopyroxene....................................................................................................................................... 30

7. Hornblende............................................................................................................................................ 34

8. Biotite.................................................................................................................................................... 36

9. Chromian spinel.................................................................................................................................... 37

10. Analyses of plagioclase in Blashke Islands Alaskan-type gabbro................................................................. 38
Characteristics and Petrogenesis of Alaskan-Type 

Ultramafic-Mafic Intrusions, Southeastern Alaska

By Glen R. Himmelbergi and Robert A. Loney2

ABSTRACT

Alaskan-type ultramafic-mafic intrusions occur along 

a belt that extends from Duke Island to Klukwan in southeastern Alaska and fall into two age groups—400 to 440 Ma; 

and 100 to 118 Ma. Most of the intrusions occur in the 

Alexander terrane or in the Gravina overlap assemblage, but 

they are not restricted to these terranes. The Alaskan-type 

ultramafic bodies range in size from sills only a few meters 

thick to intrusions about 10 km in maximum exposed dimension. Most of the bodies consist of magnetite-bearing 

hornblende clinopyroxenite or hornblendite, however many 

of the larger ones also include dunite, wehrlite, olivine 

clinopyroxenite, and, in some cases, gabbro. The Blashke 

Islands and Union Bay bodies are markedly concentrically 

zoned; dunite in the core is surrounded progressively outward by wehrlite, olivine clinopyroxenite, clinopyroxenite, 

hornblende clinopyroxenite, and gabbro. In the other large 

bodies, crude zoning may be present, but individual zones 

are discontinuous or missing entirely.

Textural, mineralogical, and chemical characteristics 

of the Alaskan-type ultramafic bodies indicate that they 

formed from a basaltic magma by crystal fractionation and 

mineral concentration processes. In general the Mg/ 

(Mg+Fe2+) ratio of olivine and clinopyroxene decreases systematically through the series dunite, wehrlite, olivine 

clinopyroxenite, clinopyroxenite, hornblende clinopyroxenite, and gabbro. The A12O3 content of clinopyroxene, which 

shows a marked enrichment with differentiation, suggests 

crystallization from progressively more hydrous melts like 

those characteristic of arc magmas. The hydrous nature of 

the magma is also indicated by the common occurrence of 

phlogopite and hornblende in wehrlite and clinopyroxenite 

and by hornblendite being part of the differentiation sequence.

1 U.S. Geological Survey and Department of Geology, University 

of Missouri, Columbia, Mo.

2 U.S. Geological Survey, Menlo Paric, Calif.

Manuscript approved for publication December 5, 1994.

Clinopyroxene in the later differentiates has a substantial 

esseneite component that is a result of the hydrous, oxidizing nature of the magma. Rare-earth-element (REE) patterns 

of the ultramafic rock samples markedly show signatures of 

cumulus origin involving accumulation of dominantly olivine, clinopyroxene, and hornblende. The absence of a positive Eu anomaly and the relatively flat REE pattern of most 

gabbro samples suggest that the gabbros are not cumulates 

but probably represent static crystallization of a differentiated liquid that had undergone substantial removal of olivine, clinopyroxene, and some hornblende. The markedly 

similar REE abundance levels and patterns for the same rock 

types in all the bodies studied suggest that all the bodies were 

derived by differentiation of closely similar parent magmas 

under near-identical conditions.

The magnesium-rich olivine in Alaskan-type dunite and 

wehrlite is consistent with crystallization from an 

unfractionated mantle-derived primary melt. The exact composition of the primary melt is uncertain, but our preferred 

interpretation is that the parental magma of most Alaskantype bodies was a subalkaline hydrous basalt. There are striking similarities between the REE abundance levels and patterns of the Alaskan-type clinopyroxenites and gabbros and 

those of the clinopyroxenite xenoliths and plutonic gabbros 

associated with Aleutian island-arc volcanism. These similarities suggest that the primary magma was probably a hydrous olivine basalt similar to the primary magma proposed 

for the Aleutian island-arc lavas. The mineral chemistry and 

phase equilibria of the ultramafic bodies suggest crystallization in magma chambers at depths of about 3 to 9 km.

The relatively small exposed size and geometry of 

many of these bodies suggest that they accumulated in 

sub volcanic feeder conduits, sills, and small magma chambers at shallow levels in the crust. We attribute the concentric zoning of rock types present in some of the bodies to 

flow differentiation in feeder conduits and sills. Only the 

Duke Island body shows abundant evidence of stratiform 

layering and ubiquitous current activity that suggest crystallization and accumulation in a small magma chamber. Although the Red Bluff Bay intrusion on Baranof Island is discussed in this report, evidence suggests that it should not be 

classified as an Alaskan-type intrusive body.

1
2 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

INTRODUCTION

The belt of ultramafic bodies that extends from Klukwan 

to Duke Island in southeastern Alaska has been known for a 

long time because of the economic interest in chromium, platinum group elements (PGE), iron, nickel, and copper 

(Buddington and Chapin, 1929; Kennedy and Walton, 1946; 

Walton, 1951). Similar bodies and associated ore deposits 

extend for almost 1,500 km through central British Columbia (Findlay, 1969; Irvine, 1976; Clark, 1980; Nixon and 

Rublee, 1988; Hammack and others, 1990; Nixon and others, 1990; Nixon and Hammack, 1991), and a third belt about 

450 km long occurs in the north-central part of the Ural Mountains of Russia and Kazakhstan (Noble and Taylor, 1960).

In 1960 these bodies were recognized as a separate, 

distinctive class of intrusions (Noble and Taylor, 1960; Taylor and Noble, 1960). Because of the concentric zoning present 

in some of the larger bodies they have been referred to as 

"zoned," "concentrically zoned," or "concentric" ultramafic 

complexes (Taylor, 1967; Wyllie, 1967; Jackson and Thayer, 

1972). The zonal structure is not universal, however, and in 

those bodies where it is present the zones are generally discontinuous and not symmetrical; only the ultramafic complex at the Blashke Islands (Walton, 1951; Himmelberg and 

others, 1986b) is symmetrically zoned. Many of the bodies 

actually consist of only one rock type. For these reasons, Irvine 

(1974) referred to this class of ultramafic bodies as "Alaskan-type" complexes because that is where the bodies were 

first recognized as distinctive. This name has been widely 

adopted and is now applied to similar ultramafic complexes 

that occur in British Columbia (Findlay, 1969; Clark, 1980; 

Nixon and Rublee, 1988; Hammack and others, 1990; Nixon 

and others, 1990), Oregon (Gray and others, 1986), California (James, 1971; Snoke and others, 1981,1982), Venezuela 

(Murray, 1972), New South Wales, Australia (Elliott and Martin, 1991), and the Ural Mountains (Taylor, 1967).

The Alaskan-type complexes are characterized as a 

separate class of intrusions by their tectonic setting, size, composition, internal structure, and mineralization. They form 

small intrusions in convergent plate-margin settings. The principal minerals in the ultramafic rocks are olivine, clinopyroxene, magnetite, and hornblende; orthopyroxene and plagioclase are extremely rare. Where a complete rock series is 

present, it includes dunite, wehrlite, olivine clinopyroxenite, 

clinopyroxenite, hornblende clinopyroxenite, hornblendite, 

and, in some bodies, gabbro. The clinopyroxenite and hornblende clinopyroxenite are generally rich in magnetite. Some 

of the larger bodies are crudely concentrically zoned; dunite 

in the core is successively ringed by wehrlite, olivine 

clinopyroxenite, and other rocks of the series. Many bodies, 

however, consist only of hornblende clinopyroxenite or 

hornblendite. Although all the bodies show evidence of origin by fractional crystallization and crystal concentration, 

extensive layering is not common. The body on Duke Island 

is an exception; it shows spectacular layering developed by

transportation and deposition of crystals by magmatic convection and density currents (Irvine, 1974). External contacts 

of all the bodies with their country rocks are sharp, steep, and 

generally marked by thermal aureoles. Mineralization, where 

present, is dominantly titanium-vanadium magnetite and platinum-group minerals (PGM).

Most of the ultramafic rocks in southeastern Alaska are 

included in the Alaskan-type group. Exceptions are the basal 

ultramafic rocks of the tholeiitic, informally named La Perouse 

layered gabbro (Himmelberg and Loney, 1981; Loney and 

Himmelberg, 1983) in the Fairweather Range, the ultramafic 

rocks associated with the norite, diorite, granodiorite complex on Yakobi Island and at Mirror Harbor on northern 

Chichagof Island (Himmelberg and others, 1987), and the 

residual mantle harzburgite exposed in the Atlin quadrangle 

southeast of Skagway (Himmelberg and others, 1986a). 

Serpentinites near Point Marsden and north of Greens Creek 

on northern Admiralty Island, and in the Coast Mountains 

south of the Taku River retain no primary mineralogy or primary structures to indicate their origin. The complete 

serpentinization, however, does indicate that they were rich 

in olivine. We do discuss the ultramafic complex at Red Bluff 

Bay (Loney and others, 1975) here with the Alaskan-type 

bodies; however, as pointed out below, inclusion of it as an 

Alaskan-type complex remains questionable.

This study describes and interprets the rock and mineral chemistry of most of the large bodies and several smaller 

ones that previous workers included as Alaskan-type complexes in southeastern Alaska. As evidenced by the characteristics of the Alaskan-type complexes listed above, recognition of these bodies as a unique group is based largely on 

field relations and petrographic characteristics. With the exception of the complexes at Union Bay (Ruckmick and Noble, 

1959), Duke Island (Irvine, 1974), and the Blashke Islands 

(Himmelberg and others, 1986b), little information has been 

available on the rock and mineral chemistry of these bodies. 

As discussed below, some of these bodies are of different 

ages, and few have the full range of field and petrographic 

characteristics of the classic concentrically zoned bodies. 

However, all are remarkably similar in rock and mineral 

chemical characteristics which, along with their field and 

petrographic characteristics, clearly establish these bodies as 

a separate class of ultramafic-mafic intrusions. All together, 

these features suggest remarkably similar petrogenetic histories for each of these bodies. We summarize the field relations and other features of these bodies to provide a framework for the discussion of the chemistry of these rocks. Thus, 

this report provides a current and comprehensive description 

of the Alaskan-type ultramafic bodies. We utilize the combined field, petrographic, structural, and chemical data to (1) 

constrain the conditions of crystallization and accumulation 

of the ultramafic bodies, (2) evaluate the nature of the parental magma composition, and (3) propose an intrusive mechanism to explain the distribution of rock types and concentric 

structure. The results of this study provide insight into the
FIELD RELATIONS AND PETROGRAPHY

complex structural and petrological processes operating at 

high crustal levels in arc environments. We believe that this 

type of understanding is crucial to development of valid petrogenetic models of arc-eruptive magmas.

REGIONAL SETTING AND AGE

The regional geologic framework of southeastern 

Alaska includes six main geologic features (fig. 1). (1) The 

Chugach terrane is composed of mostly flysch; the remainder is melange that consists of Cretaceous metaflysch and 

mafic metavolcanic rocks. (2) The Wrangellia terrane is composed of Permian and Triassic graywacke, limestone, and 

mafic metavolcanic rocks. (3) The Alexander terrane is composed of coherent, barely metamorphosed Ordovician through 

Triassic graywacke turbidites, limestone, and volcanic rocks.

(4) The Gravina overlap assemblage depositionally overlies 

the eastern margin of the Alexander terrane and consists of 

variably metamorphosed and deformed Upper Jurassic to midCretaceous flysch and intermediate to mafic volcanic rocks.

(5) The Yukon Prong terrane consists of metapelite, 

metabasalt, marble, and quartzite; it has possible ancient 

crustal affinities. (6) The Stikine terrane is composed of upper Precambrian basement rocks, some Devonian strata and 

Mississippian and Permian volcaniclastic rocks, mafic to felsic 

volcanic rocks, and carbonate rocks that were locally deformed and intruded in before Late Triassic time. The informally named Coast plutonic-metamorphic complex (Brew and 

Ford, 1984) has been superimposed on the Yukon Prong and 

adjacent terranes as a result of tectonic overlap and (or) compressional thickening of crustal rocks during collision of the 

Alexander and Wrangellia terranes with the Stikine terrane, 

the intervening Gravina overlap assemblage, and the Yukon 

Prong rocks (Monger and others, 1982; Brew and others, 

1989).

The Alaskan-type ultramafic bodies are not restricted 

to any one terrane (fig. 1). Most were intruded into the 

Alexander terrane or into the Gravina overlap assemblage. 

The Red Bluff Bay body, however, occurs west of the main 

belt of Alaskan-type bodies on the east side of Baranof Island 

in what is generally interpreted to be the Chugach terrane, 

and the Port Snettisham, Windham Bay, and Alava Bay bodies occur in rocks that are probably part of the Yukon Prong 

terrane.

The ultramafic bodies fall into two age groups. Lanphere 

and Eberlein (1966) reported K-Ar ages that range from 100 

to 110 Ma for 10 of the bodies. For the Duke Island body, 

Saleeby (1991) reported concordant U-Pb zircon ages of 108 

to 111 Ma, and Meen and others (1991) reported the ^Ar/ 

39Ar age for hornblendes of 118.5 Ma. On the basis of U-Pb 

zircon ages for gabbro pods in hornblendite at Union Bay, 

Rubin and Saleeby (1992) interpret that body to have an approximate age of 102 Ma. Loney and others (1987) reported 

data that suggest a much older age of about 429.1 Ma for the

Salt Chuck body. Similar ages were obtained by M.A. 

Lanphere (written commun., 1989) for ultramafic bodies on 

Dall Island (400.1 Ma) and Sukkwan Island (440.5 Ma).

The older group of Alaskan-type complexes was intruded into the Alexander terrane prior to collision with the 

Stikine and Yukon Prong terranes. The distribution of the 

younger group of Alaskan-type complexes in the Alexander 

terrane, the Gravina overlap assemblage, and the Yukon Prong 

terrane, however, is consistent with the interpretation that the 

Alexander terrane was adjacent to the western margin of North 

America prior to their intrusion (Rubin and Saleeby, 1992). 

The distribution and age span of the Alaskan-type complexes 

indicates long-lived arc-basaltic magmatism associated with 

the Alexander terrane. Because the older group of intrusions 

occur outboard of the younger group, an eastward migration 

of the basaltic magmatism with time is suggested. The arcbasaltic magmatism was part of a complex, ongoing, longlived, magmatic, metamorphic, and tectonic evolution of the 

convergent continental margin of western Canada and southeastern Alaska (Brew and Ford, 1985; Brew and others, 1989; 

Rubin and Saleeby, 1992).

FIELD RELATIONS AND PETROGRAPHY

Taylor and Noble (1960) reported the occurrence of 39 

ultramafic bodies that they considered to be of the Alaskantype in southeastern Alaska. Subsequently several other small 

bodies have been discovered. Most of the Alaskan-type intrusions occur in a belt referred to by Brew and Morrell (1983) 

as the Klukwan-Duke mafic-ultramafic belt. Detailed maps 

and descriptions have been published for the bodies at Union 

Bay (Ruckmick and Noble, 1959), the Blashke Islands 

(Walton, 1951; Himmelberg and others, 1986b), Duke Island 

(Irvine, 1974), Red Bluff Bay (Guild and Balsley, 1942; Loney 

and others, 1975), and Salt Chuck (Loney and Himmelberg, 

1992). Summaries of the major features of the Alaskan-type 

bodies have been given by Taylor and Noble (1960) and Taylor (1967).

This study is based on field, petrographic, and rock and 

mineral chemistry investigations of the Alaskan-type complexes at Klukwan, Haines, Douglas Island, Port Snettisham, 

Kane Peak, Blashke Islands, Union Bay, Salt Chuck, Alava 

Bay, Sukkwan Island, Dall Island, Long Island, and Red Bluff 

Bay. Although our studies of Blashke Islands (Himmelberg 

and others, 1986b) and Salt Chuck (Loney and Himmelberg, 

1992) were published separately, we include some of the data 

in this report in order to provide a single comprehensive database. Geologic maps of the Union Bay, Kane Peak, Blashke 

Islands, and Red Bluff Bay areas show the major rock types 

and characteristics of each of the bodies studied and the locations of analyzed samples (figs. 2, 3, 7, 10). Several of the 

larger bodies not included in this report are listed in table 1. 

Rock names have been changed from those in earlier publications to conform to the classification recommended by the
4 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

60° =

58° -

56° -

_YUKON 

BRITISH COLUMBIA

^Klukwan 

^Skagway

£~R~aines

uglas Island -;-;->"

:-:'4-<--:>:>-::\--/ Juneau ^Sfe^ .

Fairweather Range V\«k.i

PACIFIC OCEAN

: Petersburg :^:^:¥>>x>>>: .*.!.. v . . _ _ _ _ J_ ______ -T_ _______

EXPLANATION

Chugach terrane 

Wrangellia terrane 

Alexander terrane

Gravina overlap assemblage 

Yukon Prong terrane 

Stikine terrane

Long Island Duke Island

Alaskan-type ultramafic-mafic bodies

DIXON ENTRANCE 100 

I KILOMETERS Graham Island

54C

Figure 1. Map of southeastern Alaska showing locations of (1984), Samson and others (1989), Brew (1990), Gehrels and 

Alaskan-type ultramafic-mafic intrusions and major others (1990), Karl and others (1990), Brew and others 

tectonostratigraphic units. Map compiled from Berg and (1991), and Ford and Brew (1993). 

others (1978), Monger and others (1982), Brew and Ford
FIELD RELATIONS AND PETROGRAPHY

IUGS Subcommission on the Systematics of Igneous Rocks 

(1974). Owing to the excellent studies by Irvine (1967a, 1974), 

the Duke Island ultramafic body is not included in this study, 

but its major features are referred to in this report. Other small 

Alaskan-type intrusive bodies in southeastern Alaska not discussed here or shown on figure 1 include those at Hasselborg 

Lake, Admiralty Island (D.A. Brew, oral commun., 1991); 

Mole Harbor, Admiralty Island (Lathram and others, 1965); 

Woronkofski Island (laylor, 1967; Brew and others, 1984); 

and Sukoi Island (Taylor, 1967).

As mentioned above, it is uncertain if the Red Bluff 

Bay body should be included as an Alaskan-type intrusion. 

We therefore exclude Red Bluff Bay from the general description that follows and instead discuss its characteristics 

separately at the end of this section.

Most of the Alaskan-type ultramafic bodies are roughly 

circular to elliptical in plan with relatively steep contacts. They 

range in size from only a few meters to about 10 km in maximum exposed dimension (Union Bay, fig. 3). The larger bodies include those at Klukwan, Haines, Port Snettisham, Kane 

Peak, Red Bluff Bay, Blashke Islands, Union Bay, Salt Chuck, 

Annette Island, and Duke Island (fig. 1). Those at Blashke 

Islands, Kane Peak, Union Bay, and Duke Island contain essentially all the components of the classic concentrically zoned 

ultramafic complexes (figs. 3,7,10; table 1). Each has adunite core; wehrlite, olivine clinopyroxenite, and clinopyroxenite, which in some cases is rich in magnetite and hornblende, 

occur progressively outward. Only at the Blashke Islands, 

however, is the zoning symmetrical and continuous (fig. 10). 

Hornblendite occurs in the outer zones of Union Bay (fig. 3), 

Kane Peak (fig. 7), and Duke Island, and gabbro forms the 

outermost zones of the Union Bay (fig. 3) and Blashke Islands (fig. 10) bodies. The Annette Island body consists of 

dunite only, and the one at Salt Chuck consists primarily of 

magnetite clinopyroxenite and magnetite gabbro that are irregularly gradational. Essentially all the other ultramafic bodies, including the larger ones at Klukwan, Haines, and Port 

Snettisham, consist dominantly of magnetite-bearing hornblende clinopyroxenite and hornblendite (table 1).

The ultramafic rocks have cumulus textures that reflect 

their origin and concentration by crystal fractionation processes3 . Most of the ultramafic rocks are medium- to coarsegrained adcumulates. Textures are generally subhedral to 

anhedral granular with mutually interfering, gently curved 

grain boundary segments. Dunite and wehrlite consist of 

adcumulus olivine and interstitial postcumulus clinopyroxene, 

which is poikilitic in some wehrlite samples. Chromian spinel 

is an accessory mineral in dunite and wehrlite. At Kane Peak 

an olivine-rich peridotite with interstitial orthopyroxene, hornblende, and biotite grades into dunite and wehrlite. 

Orthopyroxene-bearing peridotite has not been observed in

3 The cumulus terminology is that proposed by Wager and others 

(1960) as redefined by Irvine (1982). Although many cumulates show evidence of originating by crystal settling, an origin is not specified in the 

definition of cumulate.

any of the other ultramafic bodies. In olivine clinopyroxenite 

and clinopyroxenite, olivine and clinopyroxene are generally 

both cumulus, chromian spinel is generally absent, but magnetite is usually present; hornblende where present is generally postcumulus in olivine clinopyroxenite but cumulus in 

clinopyroxenite. In the Salt Chuck clinopyroxenite, plagioclase is commonly present as a postcumulus or minor cumulus phase. Hornblende clinopyroxenite consists of cumulus 

clinopyroxene, magnetite, and hornblende. Magnetite is 

particularly abundant in clinopyroxenite and hornblende 

clinopyroxenite at Klukwan, Port Snettisham, Union Bay, 

and, to a lesser extent, at Salt Chuck. The Blashke Islands 

and Kane Peak bodies generally contain magnetite only as an 

accessory phase and hornblende is not abundant. Clinopyroxenite, hornblende clinopyroxenite, and hornblendite 

in most of the intrusions also contain as much as nearly 10 

percent biotite. At Kane Peak and Dall Island, biotite (phlogopite) is also present as an accessory phase in some samples 

of dunite and wehrlite.

Contacts between major rock units within any given 

complex range from gradational to sharp. Veins and dikes of 

clinopyroxenite and olivine clinopyroxenite are common in 

dunite and wehrlite. Individual rock units range from massive to internally layered. The layering is generally isomodal 

with mineral-ratio contacts and originated by gravity-settling 

or flow-differentiation processes (see: "Intrusive mechanism 

and zonal structure" discussion). In most bodies the layering 

is on the scale of centimeters in thickness and extends laterally only a few meters. At Union Bay, however, centimeterto meter-scale thick layering is common in wehrlite and olivine clinopyroxenite and extends laterally for tens to hundreds 

of meters. Spectacular examples of cross bedding, graded 

bedding, and other complex layering features occur at Duke 

Island (Irvine, 1974). Similar layering features are reported 

on the Percy Islands (Taylor, 1967) but have not been observed in the other Alaskan-type ultramafic bodies.

Of the Alaskan-type bodies studied for this report, gabbro occurs only at Union Bay (fig. 3), the Blashke Islands 

(fig. 10), and Salt Chuck (Loney and Himmelberg, 1992; fig. 

1). Gabbro also occurs at Duke Island, but it has been determined to be older than the ultramafic rocks (Irvine, 1974; 

Gehrels and others, 1987). At the Blashke Islands and Union 

Bay the gabbro forms a discontinuous outermost zone with 

sharp contacts against the adjacent ultramafic rocks. At Salt 

Chuck the clinopyroxenite and gabbro grade irregularly into 

one another by a gradual increase in postcumulus plagioclase 

in the magnetite clinopyroxenite prior to appearance of cumulus plagioclase in gabbro. Specific rock types of the gabbro unit on the Blashke Islands range gradationally and 

irregularly from olivine-bearing hornblende-pyroxene 

gabbro and gabbro-norite, near the contact with olivine 

clinopyroxenite, to hornblende gabbro toward the outer 

contact with the country rock. At Union Bay the gabbro 

unit is a relatively homogeneous gabbronorite having as much 

as nearly 5 percent each biotite and magnetite; near the 

margins, however, the mafic unit is commonly a hornblende
6 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

gabbro or diorite. Orthopyroxene is absent in the gabbros 

at Salt Chuck, but magnetite and biotite (as much as 10 

percent) are common. All the gabbros are subhedral granular 

with a grain size of about 1 to 4 mm. At the Blashke Islands 

much of the gabbro is characterized by a centimeter-scale 

flow banding that is manifested by variable concentrations of 

plagioclase and mafic minerals. The gabbros at Salt Chuck 

and Union Bay, however, are generally massive with only 

local development of plagioclase lamination or centimeterscale layering.

The enclosing country rocks of the larger ultramafic 

bodies have undergone intense contact metamorphism. Aureole widths are generally related to the size of the intrusion 

and range from less than 100 m to about 300 m. Maximum 

grade of metamorphism is generally hornblende-hornfels fades. The Kane Peak, Alava Bay, and Red Bluff Bay bodies 

have been affected by intrusion of younger granitic plutons 

(Loney and others, 1975; Brew and others, 1984; Loney and 

Brew, 1987). The Kane Peak and Alava Bay ultramafic bodies are only locally recrystallized.

The Red Bluff Bay intrusion (figs. 1, 2) is the largest 

body in a discontinuous, ill-defined, northwest-trending belt 

of ultramafic rocks on Baranof Island (Guild and Balsley, 

1942; Loney and others, 1975). The belt extends for about 70

Table 1. Major rock types and characteristics of Alaskan-type ultramafic-mafic bodies, southeastern Alaska.

Rock types Features References

Alava Bay———— Biotite-bearing hornblendite-————-——

Blashke Islands— Dunite; wehrlite; olivine clinopyroxenite; gabbronorite;

olivine hornblende gabbro; hornblende pyroxene gabbro; 

hornblende gabbro.

Dall Island———— Biotite wehrlite; biotite hornblende clinopyroxenite; 

clinopyroxenite; hornblende clinopyroxenite; biotite 

hornblendite.

Douglas Island—— Clinopyroxenite; hornblende clinopyroxenite; plagioclase 

clinopyroxenite.

Haines—————— Hornblende olivine clinopyroxenite; hornblende

clinopyroxenite; biotite magnetite clinopyroxenite.

Kane Peak———— Hornblende biotite peridotite; dunite; wehrlite; olivine 

clinopyroxenite; clinopyroxenite; hornblendite.

Elliptical shape; maximum dimension 2 km; locally 

recrystallized by granite.

Circular shape; 3.5-km diameter; concentrically zoned———

Circular shape? 0.5 to 1 km diameter; meter-scale layering 

of rock types.

This report.

Walton (1951); 

Himmelberg and 

others (1986b); 

this report

This report.

Sills several meters wide-- Brew and others 

(1987); this 

report.

Elliptical shape?; maximum dimension 8 to 10 km————— This report.

Klukwan— — Magnetite clinopyroxenite; hornblende magnetite 

clinopyroxenite.

Roughly circular shape; 3- to 3.5-km diameter; crudely 

zoned; locally recrystallized by monzodiorite.

Eliptical shape; maximum dimension 5 km—————————

Walton (1951); 

this report.

Taylor and Noble 

(1960); this 

report.

Long Island——— Plagioclase-bearing hornblendite-—————————————— Sill 6 m thick-———-—-

Port Snettisham— Hornblende magnetite clinopyroxenite; biotite magnetite 

clinopyroxenite; hornblende biotite magnetite 

clinopyroxenite.

—— This report.

Elliptical shape; 3.5-km maximum dimension------

Red Bluff Bay—— Dunite; wehrlite; clinopyroxenite—-——--

—— Thorne and Wells 

(1956); this 

report

Elliptical shape; 7-km maximum diamension. Recrystallized Guild and Balsley 

by granitic pluton. Classification as Alaskan-type (1942); Loney 

uncertain. and others

(1975); this 

report

Salt Chuck —— Clinopyroxenite; magnetite clinopyroxenite; biotite magnetite clinopyroxenite; magnetite melagabbro; magnetite 

gabbro; gabbro.

Sukkwan Island— Hornblende clinopyroxenite; hornblendite—-—-—--———-—

Union Bay———— Dunite; wehrlite; olivine clinopyroxenite; clinopyroxenite; 

magnetite clinopyroxenite; hornblende clinopyroxenite; 

hornblendite; gabbro; gabbronorite.

Annette Island—— Dunite—————————————————————————————

Duke Island——— Dunite; wehrlite; olivine clinopyroxenite; hornblende 

magnetite clinopyroxenite; hornblendite.

Percy Islands—— Olivine clinopyroxenite; hornblende magnetite 

clinopyroxenite.

Turn Mountain—— Hornblendite———————————————————

Tadpole shape; 7.3 by 1.6 km. Clinopyroxenite and gabbro 

irregularly gradational.

Tapered tabular shape; 1.5 km long-—————-———-—--- 

Elliptical shape; 11.5 by 8 km; concentrically zoned————

Elliptical shape; 1.5-km maximum dimension; two 

exposures of hornblende clinopyroxenite 1 to 3 m wide on 

periphery of dunite.

Two separate bodies exposed; 5.5 by 3.2 km and 4 by 3.2 

km, probably connected at depth; crudely zoned; 

spectacular layering developed by crystal transport and 

deposition by magmatic convection and density currents.

Circular shape; 5.5-km diameter; layering features similar to 

those on Duke Island.

Circular shape; 5-km diameterLoney and 

Himmelberg 

(1992);

Watkinson and 

Melling (1992); 

this report.

This report.

Ruckmick and 

Noble (1959); 

this report.

Taylor and Noble 

(1960).

Irvine(1974).

Stebbins (1957); 

Taylor (1967).

Brew and others 

(1984).

Windham Bay—— Clinopyroxenite; hornblende clinopyroxenite————————— Roughly circular shape; 3-km diameter————---———-— Brew and Grybeck 

(1984).
FIELD RELATIONS AND PETROGRAPHY

134° 42'

56° 51'

1 KILOMETER

EXPLANATION

Ultramafic body at Red Bluff Bay (Late Cretaceous?)— 

Consists of:

Dunite and wehrlite— In part serpentinized 

Clinopyroxenite

Kelp Bay Group (early Early Cretaceous and late Late 

Jurassic)—Greenschist, phyllite, and minor amphibolite

Contact—Dashed where approximately located

Shear zone—Dashed where approximately located; 

dotted where accompanied by talc

Shear zone followed by diabase dike 

Reef

A 60 

-0- 

20

.60

Strike and dip of foliation 

in metamorphic rocks

Inclined 

Vertical

Bearing and plunge of 

lineation in metamorphic 

rocks

Strike and dip of layering 

in ultramafic rocks

Inclined 

Vertical

X Chromite prospect

Figure 2. Geologic map of ultramafic complex at Red Bluff Bay, Baranof Island, southeastern Alaska. Map modified 

from Guild and Balsley (1942) and Loney and others (1975).
8 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

km, and, except for the Red Bluff Bay body, the ultramafic 

rocks occur as small scattered outcrops of sheared serpentinite. 

The Red Bluff Bay body consists of dunite, wehrlite, and 

clinopyroxenite, but there is no regular zoning pattern (fig. 

2). The dunite and wehrlite are gradational and have no distinct contacts or regular distribution; because the relative 

amounts of the two rock types are unknown, we include both 

of them in a single dunite and wehrlite unit. In contrast, the 

clinopyroxenite unit as mapped contains virtually no olivine 

and has sharp contacts with the olivine-bearing rocks. The 

clinopyroxenite occurs in the body as irregular masses, cumulus layers (2-50 cm thick), and crosscutting veins. The 

Red Bluff Bay body differs from the typical Alaskan-type 

intrusions in that it contains chromian spinel layers and lenses 

in concentrations great enough to have encouraged development of chromite prospects (Guild and Balsley, 1942; Loney 

and others, 1975). Likewise, in contrast to the typical Alaskan-type body, the Red Bluff Bay body contains virtually no 

hornblende, and magnetite occurs only as a secondary mineral resulting from serpentinization and recrystallization. 

Cumulus textures are preserved even though the body has 

been extensively recrystallized (see below).

Limited data suggest that the small, serpentinized bodies northwest of Red Bluff Bay were derived from ultramafic 

bodies similar to the Red Bluff Bay body. These bodies are 

mostly serpentinite with very sparse clinopyroxene grains and 

local concentrations of thin chromitite layers. The sparsity of 

clinopyroxene is partly a result of the contact metamorphism 

caused by Eocene plutons, which converted most of the 

clinopyroxene to fibrous amphibole. The chromian spinel 

largely survived metamorphism, although it is commonly 

rimmed by magnetite (Loney and others, 1975; Loney and 

Brew, 1987). As neither orthopyroxene nor serpentine pseudomorphs after orthopyroxene (bastites) have been reported in 

them, these complexes suggest that they may have been derived from clinopyroxene-bearing olivine-rich bodies such 

as the Red Bluff Bay ultramafic body.

The ultramafic complex at Red Bluff Bay is in contact 

with greenschist, phyllite, and minor amphibolite of the Kelp 

Bay Group (late Late Jurassic (Tithonian) and early Early 

Cretaceous (Berriasian)), but there is no evidence of contact 

metamorphism by the ultramafic body. The contact relations 

are obscured by shear zones along the contacts and by the 

fact that the ultramafic body lies in the upper albite-epidote 

hornfels facies part of the contact aureole of the middle Eocene 

(44.3-Ma) Baranof Lake (tonalite) pluton (Loney and others, 

1975). In the Red Bluff Bay body, the serpentine that has 

been recrystallized to antigorite and the olivine and 

clinopyroxene that have commonly reequilibrated to more 

magnesium-rich compositions indicate that they too recrystallized in response to the intrusion of the Baranof Lake pluton. On the Basis of these relations, the age of the Red Bluff 

Bay body, and the belt of serpentinites as well, lies between 

about 44 Ma and 138 Ma (Berriasian).

The dunite-wehrlite-clinopyroxenite association in the 

Red Bluff Bay body and the limits on the age of the body are 

characteristics that are similar to those of the Alaskan-type 

group of intrusions. However, the occurrence of chromitite 

lenses and layers and the virtual absence of primary magnetite and hornblende are atypical of Alaskan-type intrusions. 

The rock association, textures, and structures of the Red Bluff 

Bay body are equally compatible with an origin as crustal 

cumulates within an ophiolite complex (Coleman, 1977; 

Himmelberg and Loney, 1980; Pallister and Hopson, 1981; 

Elthon and others, 1982; Loney and Himmelberg, 1989). 

However, the absence of any orthopyroxene-bearing residual 

harzburgite in this belt of ultramafic rocks argues against these 

rocks representing a part of a dismembered ophiolite.

RELATION OF ALASKAN-TYPE

ULTRAMAFIC INTRUSIONS TO

REGIONAL STRUCTURE AND

METAMORPHISM

GENERAL STATEMENT

Intrusion of the younger Alaskan-type ultramafic bodies throughout the extensive Klukwan-Duke mafic-ultramafic belt (Brew and Morrell, 1983) during a relatively short 

interval of time, 100 to 118 Ma (Lanphere and Eberlein, 1966; 

Lanphere, written communication, 1989; Saleeby, 1991; 

Meen and others, 1991; Rubin and Saleeby, 1992), provides 

a regionally identifiable time datum. Therefore, the relation 

of the intrusions to major regional events, such as deformation and metamorphism, is critical to the study of the tectonic 

history of southeastern Alaska. Of the complexes studied, 

only those at Union Bay, Kane Peak, and the Blashke Islands 

show the critical relations of deformation and metamorphism 

in both the intrusion and the country rocks.

According to Lanphere and Eberlein (1966) and 

Lanphere (1968), the Alaskan-type ultramafic complexes of 

southeastern Alaska were intruded after folding and low-grade 

regional metamorphism of Paleozoic and lower Mesozoic 

stratified rocks of the western metamorphic belt (Dj and Mj 

of Brew and others, 1989) in Late Cretaceous time, prior to 

intrusion of plutonic rocks of the Late Cretaceous and early 

Tertiary Coast plutonic-metamorphic complex. However, evidence from this study of Union Bay and Kane Peak (fig. 1) 

and from Duke Island (Irvine, 1974) shows that these bodies 

intruded the western metamorphic belt during the late stages 

of the regional Dt deformation and Mj metamorphism and 

were affected by these events to some extent. In the Blashke 

Islands (fig. 1), however, the ultramafic intrusion and the surrounding sedimentary rocks are beyond the western limits of 

the western metamorphic belt (Brew and others, 1992) and 

were not noticeably affected by the regional metamorphism.
RELATION OF ALASKAN-TYPE ULTRAMAFIC INTRUSIONS TO REGIONAL STRUCTURE AND METAMORPHISM 9

The following discussion relies heavily on olivine 

microfabrics. Olivine microfabrics and structural states have 

proved to be important tools in the study of ultramafic rocks 

because definitive structural data are commonly difficult to 

obtain in outcrop. The optical preferred orientation of olivine 

in mafic igneous rocks may have been produced by synigneous 

mechanisms, largely laminar igneous flow and gravity settling in magma, or by postigneous tectonic deformation (Den 

Tex, 1969). Obviously the latter may be superposed upon the 

former. Orientations due to igneous processes are dependent 

on the shape of the olivine crystals, whereas tectonically produced fabrics are independent of the crystal shape (Ave 

Lallemant, 1975; Nicolas, 1992). We have used these and other 

criteria to distinguish between these processes in the Union 

Bay, Kane Peak, and Blashke Islands bodies. Because olivine is an orthorhombic mineral, the X, Y, and Z axes will 

have the following definitions in petrofabric discussions: X 

= fast ray = b = _L(010)=[010]; Y = intermediate ray = c = 

J_(001)=[001]; Z = slow ray = a = _L(100)=[100].

UNION BAY COMPLEX

The zoned ultramafic complex at Union Bay is about 

11.5 km long and about 8 km wide (figs 3,4). As mapped by 

Ruckmick and Noble (1959), and confirmed by our work, 

the intrusive body is composed of a discontinuous outer gabbro unit around an irregular, central ultramafic mass. Locally, 

such as at Union Bay itself and near Vixen Inlet, the ultramafic rocks (magnetite clinopyroxenite, unit Kupx, fig. 3) are in 

contact with the country rocks, which are composed of the 

Upper Jurassic and Lower Cretaceous Gravina sequence of 

Rubin and Saleeby (1991). As interpreted by Ruckmick and 

Noble (1959), the intrusive consists of a western, 

subhorizontal lopolithic part, about 8 km long and 4.8 km 

wide, composed dominantly of clinopyroxenite, and a smaller 

eastern vertical pipe or cylinder about 1.6 km in diameter, 

composed dominantly of dunite (figs. 3,4). In their view, the 

lopolith is a tongue-like or nappe-like body, closed on the 

west but open on the east, and was fed from a conduit now 

represented by the pipe. Beyond the contact zone, the country rocks are dominantly greenschist fades phyllite, also derived from the Gravina sequence (fig. 3). The contact zone is 

about 300 m wide. Country rock in the outer part is recrystallized to quartz-oligoclase-biotite-almandine schist. Schist 

grain size gradually increases toward the contact with the ultramafic rock and becomes noticeably coarser and more 

gneissic within about 150 m of the contact.

Our mineral fabric and field structural-geometric studies indicate that the intrusion of the ultramafic complex at 

Union Bay was contemporaneous with at least the last stages 

of folding of the country rocks. During the folding, both the 

igneous rocks of the complex and the metamorphic country 

rocks were plastically deformed about similarly oriented axial 

planes. The metasedimentary rocks were tightly folded about

northwest-trending axes and subvertical axial planes during 

the regional Mt metamorphism of the western metamorphic 

belt (late Early Cretaceous and (or) early Late Cretaceous; 

Brew and others, 1992.) The best example of this folding is 

in the northwest part of the area, in the vicinity of Vixen Inlet 

(fig. 3), where the rocks are little disturbed by the intrusion. 

The poles-to-bedding plots (+) in this area yield a Ttj axis that 

trends 303° and plunges 10° ( fig. 5A). In the contact zone, 

however, poles-to-bedding and poles-to-foliation plots (A), 

combined, yield a 7i2 axis plunging steeply to the northeast. 

This latter TC orientation appears to reflect the bending of the 

earlier folds around the solid, hot ultramafic body. A similar 

relation was observed in the Kane Peak area.

The in-dipping attitudes in the cumulus layering in the 

ultramafic rocks immediately west of Mount Burnett (figs. 3, 

55) define the hinge of an open, southeast-plunging synform 

in the complex sandwich of layers that forms the lopolith. 

Other similarly oriented but generally smaller folds occur in 

the intrusive body, and some of them extend into and involve 

the metasedimentary country rock (fig. 3). On the basis of naxis analysis (fig. 55), the synclinal axis in the igneous layering plunges about 26° to the southeast (126°). The north limb 

has an average strike of 067° and a dip of 35° south, and the 

southwest limb has an average strike of 350° and a dip of 35° 

northeast. The axial plane strikes 300° and dips 85° southwest, similar in orientation to the regional trend (fig. 5A) in 

the metamorphic rocks. The synform dies out abruptly at the 

western margin of the pipe, where a moderately to steeply 

dipping, more or less domal (quaquaversal) structure prevails.

The tectonic stresses that produced regional folding of 

the country rocks and of the layers in the Union Bay intrusion also affected the optical preferred orientation of olivine 

in the intrusion. The olivine microfabric was investigated in 

two areas in the Union Bay intrusion: (1) The eastern domal 

domain, consisting mostly of a dunite mass at the center of 

the pipe (fig. 3); and (2) the western synformal domain, centered around the south side of Mount Burnett, consisting 

mostly of interlayered dunite and clinopyroxenite in the hinge 

of the major synform in the lopolith (figs. 3, 55). Both fabrics have a similar symmetry, but the microfabric of the domal 

domain has a more pronounced preferred orientation (figs. 

6A, B). As is common in olivine tectonites, both fabrics have 

a pronounced X maximum normal to the plane containing 

maxima and partial girdles of Y and Z, the greatest maxima 

of which tend to be 90° apart. In this plane, Y lies near the 

center of the diagram (subvertical), and Z usually plunges 

gently to the northwest; weaker concentrations of Z axes form 

a girdle that ranges through horizontal to gentle southeast 

plunges. The X maximum is about normal to the axial plane 

of the synform, and accordingly the Y-Z plane lies near the 

axial plane (fig. 65) and not near the plane of the cumulate 

layering. The orientation of the layering at or near the specimen locality is shown by great circles (S) in figs. 6A, B. The 

fact that the olivine microfabric is best developed in the domal 

domain is evidence that the metamorphism was regional and
10 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

132° 00'

Sunshine Island 

O "SO

55° 

44'

2 KILOMETERS

I

80

EXPLANATION

Ultramafic complex at Union Bay (Cretaceous)—Unit of Ruckmick and Noble (1959). 

Complex zoned inward from gabbro (Kugb) at outer contact, through clinopyroxenite (Kupx) and 

wehrlite (Kuwe) to dunite (Kudu) at core

Gravina sequence (Early Cretaceous and Late Jurassic)—Unit of Rubin and Saleeby (1991). 

Consists of low-grade bedded argillite, tuff, and graywacke (KJgs), which becomes schist and 

gneiss (KJgm) in contact zone of ultramafic complex

Fault

Contact

35

V 

87GH27

Strike and dip of igneous 

cumulus layering and/or 

foliation

Sample locality and number

60

Strike and dip of sedimentary or 

volcanic bedding

Strike and dip of metamorphic foliation 

Strike of vertical metamorphic foliation

Figure 3. Geologic map of ultramafic complex at Union Bay, southeastern Alaska, showing locations of oriented samples used for 

microfabric analyses. See figure 4 for hypothetical cross section. Map modified from Ruckmick and Noble (1959).
RELATION OF ALASKAN-TYPE ULTRAMAFIC INTRUSIONS TO REGIONAL STRUCTURE AND METAMORPHISM 11

not related to local conditions. The syncline and other folds 

are manifestations of regional metamorphism accompanied 

by penetrative deformation.

The symmetrical geometry of the major units of the 

Union Bay body strongly suggests flow differentiation during emplacement (fig. 4). However, the existing olivine 

microfabric seems to be controlled by the regional deformation rather than by an original igneous processes. The regional 

metamorphism (Mt) and deformation seem to have occurred 

when the body was hot enough to permit the plastic deformation of olivine, which obscured the original igneous orientation. According to Carter and Ave Lallemant (1970), at pressures less than 5 kb, significant plastic deformation of olivine may occur at temperatures of from 300 to 400°C; this is 

consistent with the probable conditions of the low-grade Ml 

metamorphism.

KANE PEAK COMPLEX

The Alaskan-type ultramafic complex in the Kane Peak 

area crops out on the northeast coast of Kupreanof Island about

20 km northwest of Petersburg (fig. 1). It forms a 6-km2 outcrop area that is slightly elongate in a northeastward direction. Projection of the converging contacts suggests that the 

complex extends northeastward as much as 1.5 km beneath 

Frederick Sound (fig. 7). The Kane Peak complex intruded 

mainly metamorphic pelites and semipelites of the Seymour 

Canal Formation of Late Jurassic and Early Cretaceous age 

(fig. 7) (Brew and others, 1984). It has produced a vaguely 

defined contact aureole of uncertain thickness that is represented in places by coarser grained, more intensely foliated 

rocks. Along the northwest and southwest contacts the aureole is unclear because the complex is in contact with a 

migmatite unit (fig. 7) of regional extent that was also probably derived from the Seymour Canal Formation by metamorphism related to the younger 90-Ma quartz monzodiorite 

pluton (fig. 7) (Brew and others, 1984; Douglass and Brew, 

1985), which also intrudes the ultramafic complex on the west 

(Burrell, 1984; Brew and others, 1984). The pluton has recrystallized the ultramafic rocks along the mutual contact, as 

indicated by the fine polygonal crystallization of olivine and 

abundant serpentine veining in the ultramafic rocks of the 

border zone.

SECTION STRIKES ABOUT 280°

SEA LEVEL

1000-

2000

NO VERTICAL EXAGERATION

EXPLANATION

Ultramafic complex at Union Bay (Cretaceous) — Unit of Ruckmick and Noble (1959). 

Complex zoned inward from gabbro (Kugb) at outer contact, through clinopyroxenite 

(Kupx) and wehrlite (Kuwe) to dunite (Kudu) at core; dashed lines are traces of possible 

flow layers

Gravina sequence (Early Cretaceous and Late Jurassic)— Unit of Rubin and Saleeby (1991). 

Consists of low-grade bedded argillite, tuff, and graywacke (KJgs), which becomes schist 

and gneiss (KJgm) in contact zone of ultramafic complex

Figure 4. Hypothetical cross section through ultramafic complex at Union Bay, southeastern Alaska, modified from Ruckmick 

and Noble (1959, pi. 4).
12 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

The Kane Peak ultramafic complex contains hornblendite border zones, averaging about 100 m wide, along 

the northwest and southeast contacts. On the northeast, the 

complex is covered by Frederick Sound, and on the southwest the border zone seems to be absent, probably cut out by 

the younger (90-Ma) quartz monzodioritic intrusion. About 

80 percent of the poorly exposed interior of the body is composed of dunite and wehrlite that grade into one another by 

variation in clinopyroxene content. Small-scale cumulus layers occur locally, but, because of the poor exposures and the 

massive nature of the dominant rock, little is known about 

the layering. Texturally it could have formed either by static 

gravity settling or flow differentiation processes (see "Intrusive mechanism and zonal structure").

The general trend of the country rock structure on northeast Kupreanof Island is northwestward, typical of that in the 

Gravina overlap assemblage. Important elements making up 

the structural fabric are steeply eastward-dipping limbs of 

gently northwest-plunging isoclinal folds. The structural domain of the metasedimentary country rocks (fig. 7) north of 

the ultramafic complex in the Kane Peak area, and in the 

migmatite belt, is typical of this trend (fig. 8A). Poles-to-bedding plots define a n axis that plunges gently to the northwest, subparallel to the field-measured, gently plunging fold 

axes and steeply dipping axial plane. South of the ultramafic 

body, this pattern is modified; the poles-to-bedding plots define a n axis that plunges steeply east (fig. 85). This general 

attitude is shared by a steeply plunging northeastward-striking fold axis and an eastward-striking, moderately north-dip-

^" Figure 6. Equal-area, lower hemisphere plots of olivine X, 

Y, and Z axes in ultramafic complex at Union Bay, southeastern 

Alaska. Contours show concentrations of percentages (1,2,3,4,5, 

and 6 percent) per 1 percent of area. •, pole of X-maximum circle; 

S, layering (see text). A, Specimen 87GH27 from domain 1 (pipe, 

98 axes). B, Specimen 87GH38 from domain 2 (synform, 100 axes).

ping axial plane. Lineations, crenulations, mineral streaks, 

and elongations throughout this domain also have this preferred orientation, the mean lineation vector (MLV) of which 

is shown (fig. 85, Q. These data suggest that the regional 

deformation was deflected around either a preexisting ultramafic body or one that was intruded during the deformation. 

However, unlike Union Bay, there is no clear evidence 

of tectonic influence on the olivine microfabric; instead, the 

fabric appears clearly related to cumulus layering. The fabric 

was determined for two localities: One a dunite at the northeast end of the body (fig. 9A), and the other a wehrlite at the 

southwest end near Kane Peak (fig. 95). Layering was visible only in the wehrlite (great circle S in fig. 95), which also 

has a much stronger olivine preferred orientation for the X 

axis (>11 percent) than does the dunite (5 to 6 percent, fig. 

9A). Although the field-measured layering orientation is 

slightly different from that of the plane normal to the main X 

maxima, it is close enough to show the relation of the olivine 

axes to the layering: namely, X normal to the layering, and Y 

and Z near the plane of the layering. This fabric suggests that 

olivine, having pronounced (010) faces, either (1) settled in a

B

Figure 5. Equal-area, lower hemisphere plots of structural data in Union Bay area, southeastern Alaska. A, Poles to bedding (+, 

15 poles) in country rock in the Vixen Inlet area (fig. 3) and to foliation (A, 22 poles) in metamorphic contact zone of intrusion, rc, 

is for bedding, rc2 is for foliation. B, Poles to cumulus layering and igneous lamination in Union Bay ultramafic intrusion (70 poles).
RELATION OF ALASKAN-TYPE ULTRAMAFIC INTRUSIONS TO REGIONAL STRUCTURE AND METAMORPHISM 13
14 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

133° 05'

57° 

00'

L- ^~^ L- ~ LEXPLANATION

Quartz monzodiorite, quartz diorite, monzodiorite, and diorite (Cretaceous)—Correlated with 90-Ma plutons 

(Burrell, 1984; Brew and others, 1984; Douglass and Brew, 1985)

Ultramafic complex at Kane Peak (Cretaceous)—Dunite and wehrlite, mostly massive; K-Ar ages from 93.4 (biotite) 

to 102.0 (hornblende) Ma (M.A. Lanphere, written commun., 1989) 

Hornblendite—Border zone of ultramafic complex (Kuk)

Migmatite (Cretaceous)—Various migmatitic rocks, mainly agmatite and irregularly banded gneiss, mostly derived from 

Seymour Canal Formation (KJsc) (Brew and others, 1984)

Schist, semischist, and phyllite (Cretaceous and Jurassic)—Mainly pelites and semipelites derived from turbidites of 

Seymour Canal Formation (Brew and others, 1984); higher grade, more intensely foliated in narrow contact zone 

of ultramafic complex (Kuk)

50 60 i Strike and dip of metamorphic foliation

-i- Strike and dip of igneous cumulus layering Bearing and plunge of fold axes and 

67 A Strike and dip of igneous foliation 60 lineation in metamorphic rocks

-*- Strike of vertical igneous foliation 81KP11——• Sample locality and number

Contact 

Marker layer

Figure 7. Geologic map of ultramafic complex in Kane Peak area, Kupreanof Island, southeastern Alaska, showing locations of oriented 

samples used for microfabric analyses. Map modified by us from Walton (1951) with assistance of S.M. Karl and A.B. Ford on basis of 

fieldwork done in 1980.
RELATION OF ALASKAN-TYPE ULTRAMAFIC INTRUSIONS TO REGIONAL STRUCTURE AND METAMORPHISM 15

magma and came to rest with the X axis (±(010)) normal to 

the layering (Den Tex, 1969) or (2) obtained this orientation 

during magmatic laminar flow. If the crystals are elongate 

parallel to the c-crystallographic axis (= Y), then accordingly 

the Y axes would tend to be aligned parallel to the current 

direction (Brothers, 1959,1964; Nicolas, 1992). Similar flowrelated fabrics have been described by Wilson (1992) from 

the Great Dyke of Zimbabwe in which orthopyroxene crystals show a strong (8.8 percent) preferred orientation of (010) 

face parallel to layering and equally strong preferred orientation of the c axes (= Z) in the plane of the layering.

Data on the layering is very limited but do show a dominantly subvertical attitude (fig. 7). Furthermore, plots of the 

olivine Y axes (= c) of the Kane Peak ultramafic body (fig. 9) 

show a dominantly subvertical orientation that is close to that 

of the layering and is compatible with subvertical magmatic 

flow of crystals described above. This fabric could be produced by subvertical magmatic flow in a feeder conduit, such 

as proposed for flow differentiation (see "Intrusive mechanism and zonal structure"; also Nicolas, 1992). The subvertical internal orientation, coupled with the probable subvertical contacts, is more compatible with flow differentiation 

in a subvertical conduit than with gravity settling on a 

subhorizontal surface, which would require a rotation of approximately 90° to obtain its present orientation. Presumably 

such rotation would be unnecessary in diapiric intrusion 

(Irvine, 1974), but supporting evidence for this is unclear or 

absent.

BLASHKE ISLANDS COMPLEX

The massive dunite core, which forms the bulk of the 

ultramafic complex on the Blashke Islands (figs. 1,10), gives 

little indication of fine-scale layering, lamination, or other 

small scale primary igneous features. However, the general 

symmetrical configuration of rock types suggests a steeply 

dipping to subvertical cylinder. The country rocks in the 

Blashke Islands area are dominantly argillite and graywacke 

of the Descon Formation of Early Ordovician through Early 

Silurian age and are part of the Alexander terrane. Away from 

the high-grade hornfels of the contact zone, these rocks, although folded, show little indication of regional penetrative 

deformation and metamorphism of an intensity and grade that

^* Figure 8. Equal-area, lower hemisphere plots of structural 

data in metaturbidites in Kane Peak area (fig. 7), southeastern Alaska. 

A, fold axes; MLV, mean linear vector of small structural features; 

mesoscopic axial plane. A, Poles to bedding in metaturbidites north 

of migmatite belt along north border of ultramafic complex. 7ip pole 

to best-fit great circle; +, poles to bedding. B, Poles to bedding in 

metaturbidites south of ultramafic complex. n2 , pole to best-fit great 

circle; +, poles to bedding. C, Fold axes (A) and lineations (+) for 

metaturbidites in areas of plots A and B combined. Great circles 

represent axial-plane orientations in both areas; nv pole to best fit 

in plot A; n2 derived from combined bedding.

B
16 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

e
ROCK CHEMISTRY 17

would produce a syntectonic recystallization of olivine in the 

ultramafic body, such as that at Duke Island (Irvine, 1974) 

and Union Bay. Brew and others (1992) consider the Blashke 

Islands area to be outside the metamorphic and deformational 

belt that affected the Union Bay and Kane Peak bodies, In 

contrast to that at Union Bay, the Blashke Islands contact 

zone reflects this lack of tectonic influence; it is a 100-mwide zone of massive fine-grained hornfels with a well-developed granoblastic polygonal texture. The maximum-phase 

metamorphic mineral association is plagioclase-hornblendeorthopyroxene-clinopyroxene-biotite-iron oxide, indicative of 

the pyroxene-hornfels facies.

The apparent absence of a tectonic signature on the olivine microfabric of the dunite of the Blashke Islands body is 

compatible with paleomagnetic studies by Sherman C. 

Gromm6 (oral commun., 1989) that indicate the absence of 

tectonic deformation of the Blashke Islands complex. His 

data indicate tectonic folding of the Duke Island ultramafic 

complex and reinforce the conclusions of Irvine (1974). It 

appears, therefore, that Alaskan-type complexes in the southern part of the belt, at Union Bay and Duke Island, were intruded during or before the regional Ml metamorphism and 

deformation (Brew and others, 1989), whereas regional metamorphism died out to the north-northwest before it reached 

the Blashke Islands.

As in the Kane Peak complex, the olivine microfabric 

in the dunite consists of a pronounced sub vertical Y (= -L(010)) 

maximum and distinct subhorizontal X and Z maxima (fig. 

11). Also as before, this fabric is compatible with olivine crystals that have well-developed (010) faces and a pronounced 

elongation parallel to c, either by gravity settling in a magma 

or by movement during subvertical magmatic flow differentiation. In the latter process, olivine crystals having well-developed (010) faces and elongation parallel to c are brought 

parallel to the magmatic flow direction (Nicolas, 1992; see 

"Intrusive mechanism and zonal structure")- In the former 

process, according to Den Tex (1969), large crystal faces of 

mineral grains settling under gravity in a mafic magma tend 

to come to rest parallel to the surface of accumulation, and 

the crystals become aligned parallel to long dimensions only 

if a current is present. As at Kane Peak, the subvertical internal orientation and large-scale subvertical cylindrical geometry of the intrusion is more compatible with flow differentiation in a subvertical conduit than with gravity settling on a 

subhorizontal surface, which would require considerable rotation to its present orientation.

•^ Figure 9. Equal-area, lower hemisphere plots of olivine 

X, Y, and Z axes in ultramafic complex in Kane Peak area, 

southeastern Alaska. •, pole of X-maximum circle. A, Dunite 

specimen 81KP21; contours show concentrations of percentages 

(1,2,3,4,5,6, 7, and 8 (Z), 9 (Y), 10,11, and 12 (X) percent) per 

1 percent of area (97 axes). B, Wehrlite specimen 81KP11; contours 

show concentrations of percentages (1,2,3,4, and 5 (X), 6 (Y and 

Z) percent) per 1 percent of area (100 axes), S, layering.

In summary, structural and olivine microfabric studies 

of the ultramafic bodies at Union Bay, Kane Peak, and the 

Blashke Islands show different but possibly regional progressive relations relative to regional deformation and metamorphism. The Union Bay body was folded along with the country rocks during the earliest deformation and metamorphic 

event in the M, western metamorphic belt; the olivine 

microfabric indicates tectonic recystallization during this 

event. Data suggest that the Kane Peak body was possibly 

intruded during that regional deformation event, but the olivine microfabric retains an igneous signature. The ultramafic 

body at the Blashke Islands shows no evidence of being involved in the deformation of the western metamorphic belt. 

Both the Kane Peak and Blashke Islands intrusions appear to 

be subvertical, cylindrical structures that contain subvertical 

olivine microfabrics suggestive of subvertical magmatic flow. 

The absence of penetrative deformational structures in the 

country rocks surrounding the Blashke Islands body suggests 

that this area of the Alexander terrane lies outside the western limit of the western metamorphic belt.

ROCK CHEMISTRY 

MAJOR ELEMENTS

The chemical composition and Mg # [Mg/(Mg+Fe2+)] 

of CIPW normative silicates for rocks of Alaskan-type intrusions are given in table 2. The analyses were obtained by 

using X-ray fluorescence spectroscopy. FeO, Fe2O3 , and H2O 

were determined by independent methods. Dunite, wehrlite, 

and olivine-rich clinopyroxenite are partly serpentinized. In 

addition to serpentine minerals, brucite and magnetite are the 

main products of serpentinization. Coleman and Keith (1971) 

showed that, with the exception of the addition of fluids, the 

relative amounts of the major oxides do not change during 

serpentinization, and we presume that this is the case for the 

Alaskan-type ultramafic rocks. The relatively high H2O contents, the Fe2O3 contents, and the normative magnetite reported in table 2 for dunite and wehrlite reflect the degree of 

serpentinization.

Because the rocks of the Alaskan-type intrusions are 

cumulates with variable proportions of silicates and magnetite, the relation of rock chemistry to chemical trends due to 

fractionation is best indicated by the Mg # of the normative 

silicates. In the larger bodies that have a range of rock types, 

the Mg # of the normative silicates shows a substantial range 

that is generally consistent with a normal fractional crystallization trend. Slight variations from a normal trend can be 

attributed to (1) serpentinization that increases the normative 

silicate Mg #, (2) variable proportions of modal olivine, 

clinopyroxene, and hornblende each of which have different 

Mg #s, and (3) magnetite clinopyroxenite samples that have 

clinopyroxene with a high esseneite component that results 

in a Mg # which may be higher than the Mg # of rocks that 

crystallized earlier in the fractionation sequence.
18 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

132° 55'

56° 

08'

EXPLANATION 

Ultramafic complex at Blashke Islands (Early Cretaceous) — Consists of:

Dunite — Olivine and less than 2 percent chromite. Contains as much as 5 percent 

clinopyroxene near contact with wehrlite or olivine clinopyroxenite

Wehrlite — Olivine, clinopyroxene, and chromite. Mineral ratios are extremely variable 

Olivine clinopyroxenite — Clinopyroxene and olivine. Locally may contain hornblende

Gabbro — Transitional from clinopyroxene gabbro at ultramafic contact to hornblende 

gabbro at country-rock contact

Descon Formation (Early Silurian and Ordovician) — Graywacke, conglomerate,

limestone, shale, volcanic rocks. Contact-metamorphosed part (mostly homfels) stippled

Contact 65 Strike and dip of bedding in country rock

.81B101 Oriented sample locality and number
ROCK CHEMISTRY 19

•^ Figure 10. Geologic map of ultramafic complex at Blashke 

Islands, southeastern Alaska, showing locations of oriented samples 

used for microfabric analyses. Map modified from Walton (1951) 

and Himmelberg and others (1986b).

TRACE ELEMENTS

Concentrations of trace elements are summarized in 

table 3, and those of the rare earth elements (REE) are presented graphically in figure 12. On the basis of studies of 

REE abundances in other ultramafic rocks that have been 

serpentinized and metamorphosed (Pallister and Knight, 1981; 

Harnois and Morency, 1989; Harnois and others, 1990), we 

presume that the REE of the Alaskan-type complexes were 

relatively immobile during serpentinization and metamorphism and are representative of the primary rock. The chondrite-normalized REE plots were made using the computer 

program and average chondrite values supplied by Wheatley 

and Rock (1988). The REE patterns clearly distinguish the 

different units of the Alaskan-type ultramafic-mafic complexes, and the ultramafic rocks markedly show their signature of cumulus origin involving dominantly olivine, 

clinopyroxene, and hornblende accumulation. The dunites are 

dominated by olivine accumulation (>90 percent) and thus 

have very low REE concentrations (0.03-0.9 x chondrite) (fig. 

12A). The dunite REE patterns are generally flat and do not 

display the U- or V-shaped pattern characteristic of dunite 

and olivine-rich peridotite of residual origin (Pallister and 

Knight, 1981;PrinzhoferandAllegre, 1985;McDonoughand 

Frey, 1989; Harnois and others, 1990). The wehrlite samples 

show REE patterns similar to the dunites, but their higher 

REE concentration is due to cumulus clinopyroxene (fig. 12B). 

The cause of the high Ce value for the one sample of the 

Kane Peak complex ( 81KP17A, table 3) is unknown, but it 

might be related to a local weathering process (Floss and 

Crozaz, 1991) or to an undetected analytical problem. Kane 

Peak phlogopite peridotite samples (81KP2A and 81KP5A, 

table 3) show a small light REE (LREE ) enrichment compared to dunite and wehrlite samples (fig. 12C). These samples 

of olivine cumulates have significant amounts of interstitial 

hornblende and lesser amounts of interstitial phlogopite and 

plagioclase. The LREE may be concentrated in these interstitial minerals and reflect a slightly LREE-enriched 

intercumulus melt. Olivine clinopyroxenites and 

clinopyroxenites have RE concentrations that range from

^- Figure 11. Equal-area, lower hemisphere plots of olivine 

X, Y, and Z axes in ultramafic complex at Blashke Islands (fig. 10), 

southeastern Alaska. Dunite specimen 81BI01; contours show 

concentrations of percentages (1,2,3,4,5, and 6 (Y), 7 (Z), 8 and 9 

(X) percent) per 1 percent of area. •, pole of X-maximum circle.
20 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

Table 2. Chemical compositions (in weight percent) of Alaskan-type ultramafic and mafic rocks, southeastern Alaska.

[X-ray fluorescence spectroscopy analyses by A. Bartel, N. Elsheimer, K. Lewis, D. Siems, J. Taggart. Rock name abbreviations: Du, dunite; Whr, wherlite; 

Hbl, hornblende; Mag, magnetite; Ol, olivine; Phi, phlogopite; Px, pyroxene. Mg/(Mg+Fe2+), atomic ratio of normative silicates.]

Blashke Islands

Sample No. — 

Rock type —

A1203 ——— 

pg*? ———

K20 ————— 

P2O5 ————

Total ———

Mg 

(Mg+Fez+)

Sample No. — 

Rock type ——

AljOj- ——— 

fwv* rTJ2 — — — — —

PnOr r2"5

Total _ •-__«.. _ .

Mg 

(Mg+Fez+)

80BI37 

Du

80BI44 80BI48 80BI10 80BI14 80BI28 80BI17 80BI15 80BI49 

Whr Ol Cpxite Du Ol Cpxite Ol Hbl Gbn Hbl Gb Hbl Px Gb Gbn

35.60 37.30 50.80 38.50 48.60 

.00 .00 .14 .00 .31 

.31 .41 1.75 .35 3.66 

4.56 5.19 1.82 3.12 2.57 

4.84 5.04 2.96 6.82 5.25 

.17 .19 .10 .19 .14 

43.20 38.50 19.80 43.20 18.00 

.23 2.81 20.70 1.75 20.10 

.00 .00 .15 .00 .22 

.00 .00 .00 .00 .00 

.00 .00 .00 .00 .00 

9.26 9.54 1.67 5.28 .85

98.17 98.98 99.89 99.21 99.70 

.96 .96 .94 .93 .89

Kane

81KPI4A 

Cpxite

50.70 

.64 

4.70 

2.65 

6.17 

.17 

14.70 

18.70 

.65 

.74 

.00 

.25

100.07 

.85

Peak— Continued

81KP1B 

Diorite

51.10 

1.60 

13.80 

1.04 

8.33 

.17 

7.10 

9.46 

2.40 

1.88 

1.88 

.75

99.51 

.66

81KP1C 

Hblite

40.40 

1.92 

12.80 

2.49 

13.42 

.24 

10.00 

11.90 

1.70 

1.08 

.94 

.75

97.64 

.62

46.90 45.50 42.40 45.00 

.85 1.10 1.20 1.06 

16.80 19.40 19.80 17.40 

3.15 5.53 6.25 6.02 

8.23 6.09 6.16 6.73 

.21 .21 .20 .21 

7.64 5.61 6.53 7.28 

13.10 12.50 14.00 14.00 

2.20 2.39 1.80 1.75 

.19 .48 .14 .10 

.16 .20 .00 .11 

.37 .60 .80 .26

99.80 99.61 99.28 99.92 

.69 .78 .82 .80

Port Sncttisham

87GH19A 87GHI7A 

Cpxite Cpxile

36.80 

2.43 

6.55 

14.39 

9.81 

.18 

11.60 

16.50 

.40 

.73 

.19 

.09

99.67 

.94

38.00 

2.50 

6.43 

13.40 

10.25 

.27 

10.20 

18.10 

.60 

.27 

.25 

.00

100.27 

.89

80BI29 80BI19 

Hbl Px Gb Hbl Gb

43.20 46.70 

1.18 1.34 

20.00 19.30 

6.48 2.41 

6.13 7.55 

.21 .22 

5.67 4.91 

13.50 9.70 

2.19 3.44 

.20 .88 

.27 .44 

.37 2.05

99.40 98.94 

.81 .61

Salt Chuck

86GH23A 86GH20A 

Mag Cpxite Mag Cpxite

40.40 41.40 

.92 .83 

5.67 4.72 

13.89 12.56 

8.00 7.49 

.21 .20 

12.00 12.40 

17.70 19.10 

.00 .23 

.28 .00 

.02 .00 

.63 1.05

99.72 99.98 

.95 .94

86GH25A 86GH9B 

Mag Cpxite Mag Gb

41.30 40.40 

.90 .92 

5.54 15.40 

12.89 8.58 

6.57 5.68 

.18 .22 

12.10 8.00 

19.60 16.80 

.25 .65 

.06 .76 

.00 .09 

.49 2.09

99.88 99.59 

.99 .92

Union Bay — Continued

Sample No. —— 

Rock type ———

F62O3 ————

P-lOr- ....^ _. r/*O

Totalr r

Mg 

(Mg+Fez+)

87GH35A 

Ol Cpxite

49.40 

.25 

1.86 

2.52 

5.61 

.15 

20.00 

19.80 

.26 

.00 

.00 

.39

100.24 

.89

87GH41A 

Mag Cpxite

31.30 

2.22 

5.61 

21.67 

12.61 

.98 

10.50 

13.50 

.00 

.04 

.00 

.98

99.41 

.91

87GH36A 

Ol Cpxite

50.10 

.32 

2.37 

3.14 

6.17 

.23 

17.10 

20.30 

.35 

.00 

.00 

.64

100.72 

.87

87GH29A 

Mag Cpxite

39.60 

1.19 

6.63 

13.03 

9.14 

.21 

12.90 

16.50 

.46 

.11 

.00 

.68

100.45 

.90

87GH40A 

Mag Hblite

36.70 

1.98 

12.60 

10.91 

10.78 

.19 

10.70 

11.50 

1.75 

1.04 

.09 

.84

99.08 

.82

87GH37A 

Gb

49.80 

.72 

18.60 

4.65 

5.44 

.23 

4.48 

9.96 

3.43 

1.08 

.60 

.84

99.83 

.73

87GH28A 

Gbn

50.70 

.70 

16.90 

2.83 

7.26 

.20 

7.24 

11.00 

2.58 

.55 

.18 

.32

100.46 

.70
ROCK CHEMISTRY 21

Pd, peridotite; Cpxite, clinopyroxenite; Hblite, hornblendite; Gb, gabbro; Gbn, gabbronorite. Mineral abbreviations (recommended by Kretz, 1983): Bt, biotite;

Sample No. — 

Rock lype ——

SK>2 ———— 

ni Al-rfVi yji ____

SrSlZI

Najo —— 

P2o5 —— HoO— "Z" — — --•

Total- __ .

Mg 

(Mg+Fez+)

- 81SK48A 

Du

40.10 

.04 

.00 

2.09 

6.62 

.14 

46.80 

.26 

.00 

.00 

.00 

2.87

98.92 

.94

81KP7A 

Du

40.10 

.04 

.00 

1.66 

7.95 

.17 

45.70 

1.10 

.00 

.00 

.02 

2.37

99.11 

.92

81SK45A 81KP2A 

Du Hbl Phi Pd

39.60 

.04 

.00 

2.45 

8.14 

.18 

44.30 

1.28 

.00 

.00 

.00 

2.88

98.87 

.92

40.70 

.16 

1.91 

4.31 

6.56 

.19 

37.30 

1.90 

.30 

.26 

.10 

5.01

98.70 

.93

Kane Peak

81SK46A 8IKP5A 

Whr Hbl Phi Pd

42.10 

.08 

.39 

2.47 

7.76 

.17 

39.80 

4.72 

.00 

.00 

.02 

1.88

99.39 

.91

38.50 

.08 

.81 

3.46 

6.60 

.16 

42.20 

.66 

.00 

.06 

.04 

6.74

99.31 

.94

81KP20A 81KP15A 

Cpxite Cpxite

51.70 

.18 

1.13 

1.06 

4.13 

.11 

21.50 

19.80 

.00 

.00 

.00 

.25

99.86 

.91

51.90 

.24 

1.58 

1.44 

4.62 

.13 

18.70 

20.90 

.00 

.00 

.00 

.25

99.76 

.90

81KP17A 

Whr

42.70 

.08 

.48 

2.09 

9.46 

.20 

36.30 

6.54 

.00 

.00 

.00 

1.50

99.35 

.88

Salt Chuck— Continued

Sample No. — 

Rock type —

SiO2 ————

A12P3~ — —— '

Ra^fl. 1^03 ————

rfejo ——

P205 ————

Total ——— -

Mg 

(Mg+Fe/+)

86GH8A 

Bt Mag Cpxite

36.00 

1.31 

12.70 

10.16 

9.11 

.26 

8.13 

15.00 

.40 

1.56 

1.12 

1.40

97.15 

.80

86GH11A 

Mag Cpxite

41.10 

1.02 

7.35 

11.33 

7.16 

.23 

11.40 

17.80 

.45 

.41 

.10 

1.21

99.56 

.94

86GH7A 

Gb

40.70 

.94 

16.10 

6.70 

6.65 

.34 

7.03 

13.70 

1.25 

1.48 

.81 

2.85

98.55 

.80

86GHIA 

MagGb

40.50 

.74 

18.50 

7.54 

4.91 

.21 

6.30 

17.00 

.65 

.96 

.06 

2.25

99.62 

.91

86GH27A 

MagGb

43.30 

.84 

17.00 

6.79 

5.40 

.23 

6.44 

14.50 

1.62 

.98 

.40 

1.86

99.36 

.86

86GH3B 

Gb

47.20 

.61 

19.70 

4.26 

3.62 

.24 

3.67 

10.40 

1.73 

4.83 

.51 

2.47

99.24 

.82

87GH27B 

Du

38.20 

.00 

0.00 

3.63 

6.90 

.19 

45.80 

0.25 

0.21 

.00 

.00 

4.93

100.11 

.93

87GH34A 

Whr

39.00 

.00 

.16 

4.84 

6.17 

.20 

41.70 

2.34 

.18 

.00 

.00 

5.37

99.96 

.95

81KP22A 

Cpxite

50.50 

.18 

1.16 

1.20 

5.22 

.16 

23.70 

17.30 

.00 

.00 

.00 

.50

99.92 

.90

Union Bay

87GH33A 

Ol Cpxite

51.60 

.12 

1.38 

1.18 

3.24 

.10 

20.20 

21.70 

.21 

.00 

.00 

.35

100.08 

.93

81KP23A 

Ol Cpxite

42.60 

.08 

.39 

1.69 

10.00 

.20 

37.70 

5.82 

.00 

.00 

.00 

.62

99.10 

.88

87GH27A 

Du

38.30 

.04 

.39 

3.77 

11.00 

.26 

44.60 

.24 

.19 

.00 

.00 

.00

98.79 

.89

about 5 to 20 x chondrites and have open convex-upward 

patterns (figs. 12D, E, F). On the basis of mineral-melt distribution coefficients (Hanson, 1980), the ranges in concentration can be attributed largely to modal proportions of olivine 

and clinopyroxene. The RE concentrations of gabbros (5-60 

x chondrite) are generally higher than for clinopyroxenite 

(figs. 12G, H). The REE pattern for gabbro samples ranges 

from about flat to having a very slight heavy REE (HREE) 

depletion. Only two gabbro samples from the Union Bay complex show a small positive Eu anomaly suggesting plagioclase accumulation. The absence of a positive Eu anomaly 

and the relatively flat REE pattern of the other gabbro samples 

suggest that most of the gabbros are not cumulates but may 

represent static crystallization of a differentiated liquid that 

has undergone substantial removal of olivine, clinopyroxene,

and some hornblende. The highest RE concentrations (20-90 

x chondrite) are in two samples of hornblendite from the Kane 

Peak body (fig. 121).

A striking aspect of the REE is that, except for that on 

the Blashke Islands, all the complexes studied show markedly similar REE abundance levels and patterns for the various rock units. REE patterns of rocks on the Blashke Islands 

show a relative depletion in LREE compared to those of other 

bodies, thus yielding steeper slopes and crossing patterns. 

Nevertheless the overall similarity in REE patterns leads to 

the qualitative conclusion that all the complexes were derived 

by differentiation of closely similar parent magmas under 

near-identical conditions. A striking similarity between the 

REE abundance levels and patterns of the Alaskan-type 

clinopyroxenites and gabbros and those of the clinopyroxenite
22 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

100 -3

10 -

1 -

0.1 —

0.01

; I Blashke Islands

Kane Peak 

v| Union Bay

Dunite

100 -a

10 —

0.1 —

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

0.01

Salt Chuck 

Port Snettisham Clinopyroxenite

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

100 -3

o 10 -=

S

8 1

0.1 -=

0.01

0 Blashke Islands

* | Kane Peak

• Union Bay

B

Wehrlite

100 -3

10 —

1 —

0.1 —

0.01

Clinopyroxenite 

Olivine Clinopyroxenite

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

—i——i——i——i——i——i——i——i——i——i——i——i——i——i——r~ 

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

100 -3

o 10 — 

1

1 =

0.1 -=

0.01

Kane Peak

Phlogopite Peridotite

i i i i i i i i i i i i i i i 

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

100 ~3

10 —

1 :

0.1 —

0.01

Union Bay Clinopyroxenite

Olivine Clinopyroxenite

Hornblende Clinopyroxenite -i—i—i—i—i—i—i—i—i—i—i—i—i—i—r~

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Figure 12. REE patterns of ultramafic and mafic rocks of Alaskan- normalized to chondrite values given by Wheatley and Rock (1988).

type intrusions at Blashke Islands, Kane Peak, Union Bay, Salt Chuck, A, Dunite. B, Wehrlite. C, Phlogopite peridotite. D, E, and F, Clinoand Port Snettisham, southeastern Alaska. RE concentrations are pyroxenite, olivine Clinopyroxenite, and hornblende Clinopyroxenite.
ROCK CHEMISTRY 23

100 -g

o 10 —

O 1 —

0.1 —

0.01

100 -3

o 10-

o 1 —

0.1 —

0.01

100 -3

§ 10-

2

1 -

0.01

Salt Chuck

Gabbro

I I I I i i i r

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Union Bay

Blashke Islands

Gabbro

\ r I T i r i r

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

I Kane Peak Hornblendite

i i i i i i i i i i i i I i i

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

100 -a

c 10 —

1 -

0.1-

0.01

100 ~3

c 10 

.2

2

1 ;

0.1-

0.01

0 Olivine Pyroxenite

• Amphibolite

D Wehrtite

• Wehrlite Xenoliths

i i i i i i i i i i i i i i i

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

D Tholeiite

Gabbro

Gabbro 

Tholeiite

I \ I I I I T I

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Figure 13. REE patterns of ultramafic xenoliths (A), plutonic 

gabbros (B), and a tholeiite flow (B) associated with Aleutian islandarc volcanism, Alaska. RE concentrations are from Perfit and others 

(1980), Kay and others (1983), and DeBari and others (1987) and 

are normalized to chondrite values given by Wheatley and Rock 

(1988).

Figure 12. Continued. G andH, Gabbro./,Hornblendite.
24 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

Table 3. Trace-element contents (in parts per million) of Alaskan-type ultramafic and mafic rocks, southeastern Alaska. 

[Instrumental neutron activation analyses by J.R. Budahn, R.J. Knight, D.M. McKown. -, not detected. Mineral abbreviations: Bt, biotite; Hbl, hornblende;

Sample No., Rock type Ba Sr Co Ni Cr Cs Hf Rb Sb Ta Th U

Blashkc

80BI10, Dunite- ——————— -- ——— -- 13.10 

80BI37,Dunite-~ - - -— ——— -- 5.08

80BI44 Wehrlite--- -•••• -••• _ •• _ 134

80BI14, Ol Clinopyroxenite— — — — 47.5

80BI48, Ol Clinopyroxenite—-——— 19.2 

80BI15, Hbl Px Gabbro-- —— -— — —— 70.5

80BI17, Hbl Gabbro ———— — - ——— 1 63 

80BI19, Hbl Gabbro-——— — — — — 235 

80BI28, Ol Hbl Gabbronorite— — ----- 89.5 

80BI29, Hbt Px Gabbro————— — - 1 06 

80BI49, Gabbronorite— — — — — — 1 02

<2.0 

<2.0 

<4.0 

<30 

<30 

787 

669 

855 

623 

892 

654

131 

131 

119 

57.9 

42.7 

39.1 

30.4 

34.9 

39.7 

30.6 

38.8

855 

1050 

720 

113 

162 

52.5

20 

33

2190 

5870 

1640 

1230 

1520 

61.3 

26.3 

8.57 

118 

14.9 

80.7

0.085 

.013 

.11 

.15 

.14 

.11 

.196 

.183

.11

0.115 

.0738 

.0583 

.135 

.135 

.618 

1.10 

1.20 

.805 

.933 

.557

3.2 

1.7 

3.9 

3.9 

3.9 

<1.0 

<1.0 

16.8 

3.1 

<1.0 

6.1

0.045

.088

.31

<.062 

<.075 

.187 

.14 

.095 

.091

0.0342 

.0161 

.0499 

.025 

.025 

.069 

.128 

.225 

.0942 

.133 

.0453

0.010 

.0184 

.027 

<.050 

<.050 

<.050 

.590 

.435 

<.050 

.0952 

<.050

0.0239 

.0060 

.0221 

<.050 

.013 

.30 

.297 

.223 

<.050 

.051 

.074

Kanc

8 1KP7A, Dunite— ——— - — 11

81SK045A, Dunite —— - —— - ———— - 1 2.5 

8 1 SK048A, Dunite —— - ———— - — — - 5 . 6 

81 KP2A, Hbl Phi Peridotite— — — —— 90.7 

8 1 KP5 A, Hbl Phi Peridotite————— 31.5 

81KP17A, Wehrlite— - ——— —— - — 9.6 

81KP20A, Clinopyroxenite————— 4.2 

81SK046A, Wehrlite ——————— —— 30.6 

8 1 KP23 A, Ol Clinopyroxenite——— 8 . 1 

81KP14A, Clinopyroxenite————— 247

81KP15A, 28.4

8 1 KP22A, Clinopyroxenite--———— 3 5 

SIKPlB.Diorite— - - -213

8 1 KP1C, Hornblendite —— —— —— —— - 1 7 7

12 

<10 

<10 

110 

19 

14 

24 

<10 

1 1 

89.7 

125 

66.2 

415 

281

127 

136 

128 

116 

126 

123 

44.8 

127 

119 

50.3 

51.6 

56.8 

29.7 

54.5

1750 

1340 

2110 

1310 

1630 

825 

316 

1120 

865 

98.4 

203 

291 

95.1 

46.4

2460 

3090 

3590 

2870 

3220 

920 

2480 

1530 

1410 

213 

1360 

2130 

253 

84.3

0.016 

.066 

.036 

.302 

.065 

.023 

.034 

.032 

.092 

.398 

.054 

.12 

.559 

.154

0.168 

.067 

.053 

.419 

.166 

.0433 

.0518 

.12 

.028 

1.62 

.268 

.228 

2.21 

2.30

0.63 

<.37 

<.32 

3.16 

1.4 

.63 

<.55 

<.44 

.62 

29.6 

3.6 

4.39 

15.4 

11.5

0.091 

.14

.26 

.080

.20 

.12 

.154 

.36 

.14

0.0067 

.0084 

.0083 

.0752 

.0211 

.0039 

.0096 

.0159 

.0199 

.102 

.0565 

.0279 

.403 

.262

0.0605 

<.0085 

.0087 

.661 

.179 

.017 

.035 

.029 

.025 

.244 

<.050 

.0574 

1.69 

.368

0.0415 

.0065 

.011 

.304 

.114 

.0063 

.016 

.0365 

.015 

.124 

.03 

.017 

1.14 

.193

Salt

86GH8A, Bt Mag Clinopyroxenite— 659 

86GH11A, Mag Clinopyroxenite—— 126

86GH20A, Mag 70 

86GH23A, Mag 1 04 

86GH25A, Mag Clinopyroxenite —— 52.6 

87GH42A, Bt Mag Clinopyroxenite- 749 

87GH43A, Bt Mag Clinopyroxenite- 70.8 

86GH I A, Mag GabbroTM— ———— —— 24 1 

86GH3B, Gabbro ————— - ————— 687

86GH7 A, Gabbro— — - - —— 480

86GH9B, Mag Gabbro ——————— 1 7 2 

86GH27A, Mag Gabbro —— —— —- — 360

1100 

331 

<310. 

87.2 

85 

1160 

391 

1480 

1860 

1530 

1240 

1480

71.1 

61.9 

65.7 

64.8 

63.5 

68.5 

67.6 

41.2 

24.8 

42.5 

49.6 

39.8

46.2 

51 

28.7 

40.2 

45 

39.4 

48.2 

19.7 

6.7 

24 

38 

22.3

5.56 

14.0 

12.3 

18.3 

26.9 

8.46 

5.86 

8.81 

1.90 

2.3 

5.57 

5.06

0.479

.24 

.123

.465 

.043 

.351 

.332 

.340 

.19 

.322

l.ll 

1.64 

.671 

.578 

.657 

1.03 

1.43 

1.02 

1.27 

1.04 

1.14 

.952

39.2 

9.96 

<1.0 

7.44 

6.8 

40.4 

9.6 

25.5 

130 

37.2 

19.9 

24.6

0.073 

.30 

.765 

.18

.114 

1.19 

.196 

.124 

.22 

.137

0.0372 

.016

.116

.057 

.069 

.0318 

.0426 

.023 

.0161 

.020

0.453 

.606 

.242 

.104 

.10 

.464 

.433 

.278 

2.19 

.850 

.281 

.309

0.184 

.24 

.072 

.014 

<.050 

.108 

.126 

.123 

1.04 

.305 

.120 

.0793

Port

87GH17A, Clinopyroxenite———— 64

87GH19A, Clinopyroxenite-———— 150

120 

170

63.3 

76.4 51.7

14.2 

25.6

0.31 

0.21

1.35 

0.804

<1.0 

13.4

0.20 

.14

0.108 

.039

0.160

.11

0.058 

<.050

Union

87GH27 A, Dunite-- — — - ——— <2.7

87GH27B, Dunite —— - — - ————— 4.2 

87GH34A, Wehrlite-—— ——— - ——— - 8 . 9 

87GH33A, Ol Clinopyroxenite——— 35.9 

87GH35A, Ol Clinopyroxenite——— 26.4 

87GH36A, Ol Clinopyroxenite——— 1 3 

87GH49A, Ol 1 9.4 

87GH41A, Mag Clinopyroxenite— -- 29.1 

87GH47A, Clinopyroxenite————— 1 9 

87GH29A, Mag Clinopyroxenite—- 46 

87GH40A, Mag Hornblendite———— 1 6 1 

87GH28A, Gabbronorite——————— 2 1 0

87GH37A Gabbro—— _ _ - — _ 533

87GH44A, Gabbro———— ————— -- 473

<IO 

<10 

<IO 

<30 

32 

<30 

80 

33 

89 

35.0 

440 

917 

1120 

1320

153 

125 

121 

38.6 

60.3 

57.9 

43.3 

107 

52.3 

79.4 

87.9 

34.6 

27.5 

29.1

1380 

873 

111 

186 

184 

162 

320 

84.6 

76.1 

79.4 

29 

79.0 

11.7 

17

11800 

2930 

2660 

3690 

1720 

762 

3360 

52.3 

550 

26.8 

5.76 

300 

10.3 

3.37

.013 

.021

.14 

.29

.021 

.053 

.13

.160

0.040 

.026 

.026 

.098 

.18 

.583 

.136 

.438 

.691 

.416 

1.14 

.553 

.493 

.537

<0.34 

<.48 

<.61 

2.7 

1.8 

3.5 

4.6 

4.3 

1.62 

2.4 

7.5 

3.9 

8.51 

5.0

.16 

.11

.41 

.096 

.30 

.552 

.494 

.235 

.082 

.051

0.0221 

.0041 

.0051 

.063 

.058 

.043 

.049 

.221 

.0075 

.112 

.0762 

.0460 

.0418 

.0400

<0.0044 

<.0086 

<.014 

.0339 

.032 

<.050 

<.050 

.22 

.176 

.0366 

.849 

.13 

.372 

.237

<0.0030 

<.0008 

<.0031 

.0224 

.0363 

.028 

.0216 

.0335 

.0477 

.051 

.219 

.044 

.12 

<.050
ROCK CHEMISTRY 25

Mag, magnetite; Ol, olivine; Phi, phlogopite; Px pyroxene.]

Zn Zr Sc La Ce Nd Sm Eu Gd Tb Tm Yb Lu Sample No., Rock type

Islands

74.4

67.2

72.7

.

-

80.2

87.5

62.9

92.1

100

89.9

m

23

.

41

-

31

52

86.8

36

41

37.5

12.4

5.32

16.3

109

89.7

40.7

33.3

36.8

46.2

34.2

51.9

0.0450

.0254

.0414

.295

.179

2.10

7.27

7.77

5.69

6.60

3.22

0.140

.058

.17

.

.

4.80

16.3

22.7

13.4

14.8

7.84

0.12

.029

.16

1.54

.72

6.71

11.1

19.1

8.72

14.1

8.02

0.0503

.0079

.0740

.600

.348

2.30

3.10

5.49

2.57

3.90

2.53

0.0191

.0042

.0290

.273

.151

.980

1.09

1.73

.931

1.39

.958

0.074

.

.11

.

.

3.01

3.57

6.62

3.10

4.62

3.26

0.0149

.0050

.0241

.180

.121

.505

.559

1.02

.492

.701

.556

.

0.0059

.

.

-

.278

.345

.549

.310

.405

.308

0.07820.0124

.0444 .0063

.0946 .0147

.524 .0802

.28 .0492

1.58 .219

2.19 .338

3.35 .441

1.96 .275

2.31 .319

1.82 .257

8QBI10, Dunite.

80BI37, Dunite.

80B144, Wehrlitc.

80B114, Ol Clinopyroxenite.

80BI48, Ol Clinopyroxenite.

80BI15, Hbl Px Gabbro.

SOB 1 17, Hbl Gabbro.

80BI19, Hbl Gabbro.

80BI28, Ol Hbl Gabbronorite.

SOB 129, Hbl Px Gabbro.

80BI49, Gabbronorite.

Peak

59.2

60.2

55.5

80.7

63.0

65.5

53.1

55.5

72.2

114

58.5

53.9

116

148

<1.9

11

3.2

13

5.0

21

25

16

11

61.5

12

23

127

111

5.74

6.18

3.38

6.33

3.96

19.8

52.2

13.5

17.6

75.1

59.9

43.9

50.9

53.0

0.286

.0929

.0597

3.54

1.09

.207

.565

.341

.194

5.65

1.19

.845

29.0

16.1

0.593

.32

.13

6.71

2.18

10.6

2.4

.982

.931

16.6

3.43

2.34

77.0

55.2

0.37

.25

.065

3.21

1.09

1.00

2.56

.71

.921

11.6

3.55

2.81

51.0

39.6

0.112

.0829

.0188

.857

.298

.337

.92

.249

.304

3.58

1.37

1.19

13.7

9.71

0.0414

.0315

.0089

.280

.102

.126

.346

.0954

.110

1.08

.443

.363

2.75

3.08

0.13

.12

.

.843

.32

.43

1.22

.32

.34

3.47

1.53

1.25

13.9

9.27

0.021

.018

.0047

.109

.0505

.0663

.189

.0525

.0512

.445

.185

.165

1.82

1.20

.

.

0.045

-

.

.055

.02

.

-

.

-

.685

.485

0.0543 0.0074

.0769 .0117

.023 .0033

.255 .0367

.136 .0196

.0976 .0130

.292 .0330

.109 .0137

.0702 .01

1.18 .164

.341 .0428

.313 .0390

3.60 .478

2.67 .360

81KP7A, Dunite.

81SK045A, Dunite.

81SK048A, Dunite.

81KP2A, Hbl Phi Peridotite.

81KP5A, Hbl Phi Peridotite.

81KP17A, Wehrlite.

81KP20A, Clinopyroxenite.

81SK046A, Wehrlite.

81KP23A, Ol Clinopyroxenite.

81KP14A, Clinopyroxenite.

81KP15A, Clinopyroxenite.

81KP22A, Clinopyroxenite.

81KP1B, Dioritc.

81KP1C, Hornblendite.

Chuck

124

94.1

-

93.2

117

134

106

80.1

87.7

130

81.1

85.9

96.8

-

31

.

148

500

52.8

42

.

54.0

29

33.0

81.5

107

103

98.1

32.2

75.9

37.3

13.5

27.4

41.0

35.0

7.83

6.24

2.35

2.03

2.22

9.33

4.60

3.97

18.1

14.0

4.37

11.5

21.2

15.2

6.24

5.61

5.06

25.1

12.0

10.6

40.9

34.4

12.2

26.8

18.7

15.3

5.64

4.30

6.26

18.9

10.0

9.54

24.4

25.8

11.2

17.7

5.37

4.55

1.76

1.66

2.16

5.77

3.70

3.32

5.93

6.67

3.98

4.81

1.63

1.52

.596

.656

.833

1.79

1.25

1.07

1.75

2.05

1.26

1.56

5.57

.

2.3

2.25

.

6.11

4.84

3.49

5.10

6.73

4.98

4.68

0.808

.765

.328

.32

.449

.852

.744

.486

.743

.902

.657

.641

0.312

.329

-

.

.

.325

.291

.211

.339

.373

.289

.330

1.7T 0.244

1.78 .247

.709 .0927

.736 .0982

.935 .132

1.84 .251

1.60 .229

1.2 .168

2.15 .291

2.20 .291

1.70 .230

1.90 .259

86GH8A, Bt Mag Clinopyroxenite.

86GH11A, Mag Clinopyroxenite.

86GH20A, Mag Clinopyroxenite.

86GH23A, Mag Clinopyroxenite.

86GH25A, Mag Clinopyroxenite.

87GH42A, Bt Mag Clinopyroxenite.

87GH43A, Bt Mag Clinopyroxenite.

86GH1A, Mag Gabbro.

86GH3B, Gabbro.

86GH7A, Gabbro.

86GH9B, Mag Gabbro.

86GH27A, Mag Gabbro.

Snettishant

159

111

103 74.1

79.7

3.60

1.59

10.1

5.17

8.86

5.50

2.88

1.99

1.07

.741

3.55

-

0.481

.275

.

-

0.962 0.145

.462 .0689

87GH17A, Clinopyroxenite.

87GH19A, Clinopyroxenite.

Bay

3

4

62.5

78.1

73.7

176

1 1

128

98.6

123

98.0

91.5

106

91.3

6.7

17

14

19

38

53.1

25

39

9.4

33

.

45

.

38.3

4.46

3.98

8.44

64.1

73.2

93.8

46.5

84.2

75.3

79.9

66.7

34.9

21.6

20.7

0.0233

.0257

.091

.340

.524

1.45

.326

1.04

1.87

1.20

2.82

5.58

15.0

13.7

0.045

<.054

.31

1.27

1.82

4.55

.947

2.93

6.77

4.06

6.88

12.0

31.9

29.9

<0.024

.037

.25

1.39

2.09

4.74

.875

2.90

6.96

4.78

8.21

8.17

19.4

16.3

0.0062

.0133

.0769

.549

.846

1.74

.363

1.14

2.61

1.89

3.14

2.44

4.74

3.97

0.0021

.0049

.0270

.209

.315

.642

.143

.441

.977

.696

1.25

1.05

1.62

1.84

.

0.090

.740

1.08

2.20

.492

1.57

3.45

2.29

.

2.51

4.29

3.74

<0.0015

.0033

.014

.112

.16

.339

.0819

.255

.569

.345

.588

.388

.601

.543

.

.

.

.

-

.

.

0.272

.

.

.228

.300

.264

0.0088 0.0015

.013 .0021

.040 .0049

.266 .0360

.395 .0546

1.05 .145

.198 .0281

.635 .0835

1.66 .220

.850 .111

1.15 .147

1.39 .209

1.80 .251

1.56 .224

87GH27A, Dunite.

87GH27B, Dunite.

87GH34A, Wehrlite.

87GH33A, Ol Clinopyroxenite.

87GH35A, Ol Clinopyroxenite.

87GH36A, Ol Clinopyroxenite.

87GH49A, Ol Clinopyroxenite.

87GH41A, Mag Clinopyroxenite.

87GH47A, Clinopyroxenite.

87GH29A, Mag Clinopyroxenite.

87GH40A, Mag Hornblendite.

87GH28A, Gabbronorite.

87GH37A, Gabbro.

87GH44A, Gabbro.
26 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

xenoliths and plutonic gabbros associated with Aleutian island-arc volcanism (fig. 13) (Perfit and others, 1980; Kay 

and others, 1983; DeBari and others, 1987) allows the Aleutian volcanic rocks to serve as models for constraining the 

parental magma composition of the Alaskan-type complexes.

MINERAL CHEMISTRY

Mineral chemistry and trends in mineral chemistry are 

among the best indicators of chemical fractionation trends of 

magmas which, in turn, reflect the composition of the parent 

magma(s) and the physical conditions of crystallization. 

Chemical compositions and structural formulas of olivine, 

orthopyroxene, clinopyroxene, hornblende, biotite, chromian 

spinel, and plagioclase are arranged in tables 4 through 10, 

respectively, by location and decreasing Mg # [Mg/ 

(Mg+Fe2+)] for Fe-Mg silicates, Cr # [Cr/(Cr+Al)] for 

chromian spinel, and anorthite (An) content for plagioclase. 

All minerals were analyzed with a JEOL model 733 

Superprobe at Washington University, St. Louis, Missouri. 

Matrix corrections were made by the method proposed by 

Bence and Albee (1968) using the correction factors of Albee 

and Ray (1970). Because of the high oxygen fugacity of the 

magma, at least by the time of crystallization of abundant 

magnetite, structural formulas for pyroxene, hornblende, and 

chromian spinel were calculated by normalizing to a fixed 

number of cations, and Fe3* and Fe2+ were calculated from 

charge balance. Calculation of Fe3+ and Fe2+ by this procedure is subject to bias resulting from errors in the analysis, 

particularly for Si, and the procedure might yield Mg #s that 

are erroneously high for low-iron minerals. Nevertheless, 

Loney and Himmelberg (1992) showed the method to be effective for clinopyroxene in the Salt Chuck intrusion. Olivine structural formulas were normalized to 4 oxygens, and 

biotite formulas were calculated by normalizing to 11 oxygens 

with all iron as FeO, which obviously introduces some error.

In general the Mg # of olivine and clinopyroxene decreases systematically through the series dunite, wehrlite, 

olivine clinopyroxenite, clinopyroxenite, hornblende clinopyroxenite, and gabbro. At Red Bluff Bay the olivine Mg # 

ranges from 0.949 in dunite to 0.897 in clinopyroxenite. These 

values are substantially higher than those for corresponding 

rock types in the other bodies, and we interpret them to reflect reequilibration during regional thermal metamorphism 

imposed by the Tertiary intrusions. The clinopyroxene Mg # 

at Red Bluff Bay, however, ranges from 0.974 in wehrlite to 

0.934 in clinopyroxenite and is comparable to values for similar rock types at Kane Peak and some at Union Bay, although 

those at Union Bay have higher esseneite components.

Excluding the Red Bluff Bay intrusive, the Mg # of 

olivine varies as follows: In dunite 0.912 to 0.863, with most 

values between 0.902 and 0.891 (table 4); in wehrlite 0.901 

to 0.846; and in olivine clinopyroxenite-clinopyroxenite from 

about 0.882 to 0.804, although one sample of clinopyroxenite 

from Union Bay has a value of 0.744, which is about the

same as for olivine in a Blashke Islands gabbro sample (0.766). 

On the basis of the most Mg-rich, nonmetamorphic olivine 

composition and simple olivine-melt equilibria at 1-bar pressure (Roeder and Emslie, 1970), a minimum Mg # of about 

0.75 is indicated for the dunite parent magma; the value would 

be higher for higher pressures (Ulmer, 1989).

The major chemical variations in pyroxene are illustrated in figures 14 and 15. Orthopyroxene is rare in the ultramafic rocks and was observed as a common constituent 

only in oli vine-rich peridotite at Kane Peak, where it has a 

Mg # of 0.89 (table 5) and coexists with olivine of about the 

same Mg #. On the other hand, orthopyroxene is common in 

the gabbroic rocks at Union Bay and the Blashke Islands. 

Many of the samples are gabbronorite, and the Mg # ranges 

from 0.748 to 0.532

According to the calculation and classification scheme 

of the International Mineralogical Association (IMA; 

Morimoto and others, 1988) all clinopyroxene in the ultramafic rocks and most clinopyroxene in the gabbros would be 

classified as diopside. However, Loney and Himmelberg 

(1992) showed that clinopyroxenes in magnetite 

clinopyroxenite and gabbro of the Salt Chuck intrusion have 

a substantial Fe3+ content, most of which is in the esseneite 

component and thus not accounted for in the IMA calculation procedure. Thus we adopted the approach used by Loney 

and Himmelberg (1992) and have calculated the Wo, En, and 

Fs components of the clinopyroxenes (table 6) using the calculation scheme of Lindsley and Andersen (1983). When projected onto the pyroxene quadrilateral (fig. 14), most of the 

clinopyroxenes plot as Mg-rich augite.

The A12O3 content of clinopyroxene shows a marked 

enrichment with differentiation, as indicated by cumulus assemblages and Mg # of the clinopyroxene (fig. 15). The trend 

is similar to that shown by clinopyroxene in arc cumulates 

(Conrad and Kay, 1984; DeBari and others, 1987; DeBari 

and Coleman, 1989; Loucks, 1990) and contrasts with the 

trend typically observed in low-pressure anorogenic igneous 

provinces such as midocean ridges or back-arc basins 

(Himmelberg and Loney, 1980; Pallister and Hopson, 1981; 

Elthon and others, 1982; Komor and others, 1985; Loney and 

Himmelberg, 1989; Loucks, 1990). Using data from three 

Alaskan-type ultramafic bodies (Duke Island and Union Bay 

Alaska, and Tulameen, British Columbia) as well as from 

other arc-cumulate suites, Loucks (1990) demonstrated that 

the trend of the Aliv/TiO2 ratio in clinopyroxene in arc cumulates is distinct from that trend in rift-related tholeiites; the 

differences in the trends and the usefulness of this discrimination diagram is further substantiated by the data presented 

here (fig. 16).

The increase with differentiation of A1 2O3 in 

clinopyroxene has been used to support the hypothesis that 

after fractionation of ultramafic cumulates, the residual 

magma, parental to arc crust, is a high-alumina basalt (Murray, 

1972; Conrad and Kay, 1984; Kay and Kay, 1985a, b). The 

trend of alumina enrichment with differentiation also has 

been thought to reflect crystallization of clinopyroxene
MINERAL CHEMISTRY 27

Table 4. Analyses of olivine in Alaskan-type ultramafic and mafic rocks, southeastern Alaska.

[Electron microprobe analyses (in weight percent) by G.R. Himmelberg. Blashke Islands analyses from Himmelberg and others (1986b). Abbreviations given in table 2. 

Mg/(Mg+Fe+Mn), atomic ratio of normative silicates. -, not detected; n.d., not determined.]

Blashke Islands

Sample No. — 

Rock type —

SiO2 ———— 

FeO*

MgO ———— 

Total- ——

80BI37 

Du

42.00 

9.51

49.40 

.17 

.10

101.18

80BI5 

Du

41.10 

10.50 

.02 

48.10 

.26 

.09

100.07

80BI6 

Du

41.40 

10.50 

.02 

48.20 

.21 

.09

100.42

80B110 

Du

41.10 

10.60 

.03 

48.60 

.05 

.10

100.48

80BI43 

Du

40.80 

10.40

47.90 

.18 

.07

99.35

80BI12 80BI44 

Du Whr

41.10 41.40 

11.90 11.90 

.07 .07 

47.20 47.20 

.08 .08 

.04 .11

100.39 100.76

80BI13 

Ol Cpxite

41.40 

12.00 

.02 

47.40 

.07 

.04

80BI47 80BI14 

Whr Ol Cpxite

40.30 

12.40 

.03 

47.50 

.09 

.04

100.93 100.36

38.70 

17.90 

.28 

41.90 

.37 

n.d.

99.15

Dall Island

80BI15 

Gabbro

39.00 

20.90 

.77 

39.80 

.17 

.08

100.'72

90GH6A 

Phi Whr

40.89 

11.01 

.16 

49.05 

.03 

.31

101.46

Cations per 4 oxygens

Si »-_

Mg

(Mg+Fe+Mn)

1.013 

.192

1.776 

.004 

.002

.903

1.008 

0.215 

.000 

1.759 

.007 

.002

.891

1.011 

.215 

.000 

1.755 

.005 

.002

.891

1.005 

.217 

.001 

1.770 

.001 

.002

.891

1.008 

.215

1.763 

.005 

.001

.891

1.011 1.014 

.245 .244 

.001 .001 

1.730 1.723 

.002 .002 

.001 .002

.875 .875

1.012 

.245 

.000 

1.727 

.002 

.001

.875

0.996 

.256 

.001 

1.749 

.002 

.001

.872

0.996 

.385 

.006 

1.607 

.010 

.000

.804

1.002 

.449 

.017 

1.524 

.005 

.002

.766

0.994 

.224 

.003 

1.778 

.001 

.006

.887

Kane Peak

Sample No.-- 81 SK48A 

Rock type — Du

p~O*..

Total ———

40.44 

8.53 

.13 

50.38 

.14 

.27

99.87

81KP7A 

Du

40.06 

9.44 

.17 

49.55 

.01 

.24

99.46

81KPI7A 

Whr

40.14 

9.47 

.16 

49.39 

.02 

.27

99.44

81SK45A 

Du

40.01 

10.94 

.20 

48.39 

.06 

.20

99.79

81SK43A 81KP2A 81SK46A 

Whr Hbl Phi Pd Whr

39.92 

11.59 

.19 

48.40 

.03 

.14

100.25

39.36 39.65 

12.18 12.48 

.20 .20 

47.26 47.52 

.00 .04 

.24 .21

99.23 100.09

81KP5A 

Hbl Phi Pd

39.77 

12.52 

.25 

47.43 

.00 

.24

100.20

81KP23A 

Ol Cpxite

39.40 

14.61 

.25 

46.08 

.02 

.14

100.49

81KP20A 

Whr

39.27 

14.47 

.21 

45.11 

.00 

.16

99.21

81KP22A 

Cpxite

39.06 

14.87 

.21 

45.42 

.02 

.16

99.72

81KP15A 

Cpxite

38.66 

17.61 

.24 

43.12 

.02 

.10

99.74

Cations per 4 oxygens

Me

Mg

(Mg+Fe+Mn)

0.989 

.174 

.003 

1.836 

.004 

.005

.912

0.988 

.195 

.003 

1.821 

.000 

.005

.902

0.990 

.195 

.003 

1.815 

.001 

.005

.901

0.990 

.226 

.004 

1.784 

.002 

.004

.886

0.986 

.239 

.004 

1.782 

.001 

.003

.880

0.986 0.986 

.255 .259 

.004 .004 

1.764 1.760 

.000 .001 

.005 .004

.872 .870

0.987 

.260 

.005 

1.755 

.000 

.005

.869

Red Bluff Bay

Sample No.--- 90GH16A 

Rock type — Du

SiC>2 ————

Cff\ *

Total- ——

41.69 

5.02 

.06 

52.97 

.01 

.20

90GH11A 90GH18A 

Du Whr

41.57 

6.23 

.17 

52.03 

.01 

.45

99.95 100.45

41.17 

7.51 

.19 

51.09 

.01 

.33

100.30

90GH15A 

Whr

41.02 

9.12 

.15 

49.98 

.00 

.39

100.66

0.985 

.305 

.005 

1.717 

.001 

.003

.847

Union Bay

90GH15B 87GH27B 87GH49A 87GH34A 87GH33A 

Cpxite Du OlCpxite Whr Cpxite

40.52 

9.91 

.18 

49.29 

.00 

.35

100.24

40.19 39.52 

10.21 11.19 

.19 .18 

48.69 47.86 

.17 .00 

.12 .17

99.56 98.91

39.93 

11.60 

.21 

48.12 

.08 

.11

100.04

39.23 

12.87 

.23 

46.62 

.01 

.11

99.06

0.993 

.306 

.004 

1.700 

.000 

.003

.846

0.985 

.314 

.004 

1.708 

.000 

.003

.843

87GH27A 87GH35A 

Du Cpxite

39.60 

12.89 

.24 

46.44 

.22 

.19

99.57

38.65 

18.18 

.28 

42.67 

.03 

.12

99.93

0.987 

.376 

.005 

1.642 

.000 

.002

.812

87GH36A 

Ol Cpxite

37.45 

23.35 

.34 

38.60 

.02 

.05

99.79

Cations per 4 oxygens

n_

Mg

(Mg+Fe+Mn)

1.000 

.101 

.001 

1.894 

.000 

.004

.949

0.999 

.125 

.003 

1.864 

.000 

.009

.935

0.997 

.152 

.004 

1.844 

.000 

.006

.922

0.997 

.185 

.003 

1.810 

.000 

.008

.906

0.993 

.203 

.004 

1.800 

.000 

.007

.897

0.993 0.988 

.211 .234 

.004 .004 

1.793 1.783 

.004 .000 

.002 .003

.893 .882

0.988 

.240 

.004 

1.775 

.002 

.002

.879

0.987 

.271 

.005 

1.748 

.000 

.002

.864

0.991 

.270 

.005 

1.733 

.006 

.004

.863

0.988 

.389 

.006 

1.626 

.001 

.002

.805

0.984 

.513 

.007 

1.511 

.001 

.001

.744

* Total iron as FeO.
28 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

Table 5. Analyses of orthopyroxene in Alaskan-type ultramafic and mafic rocks, southeastern Alaska.

[Electron microprobe analyses (in weight percent) by G.R. Himmelberg. Blashke Islands analyses from Himmelberg and 

others (1986b). Abbreviations given in table 2. Mg/(Mg+Fe2+), atomic ratio of normative silicates, n.d., not determined.]

Blashke Islands

Sample No.- - 

Rock type- -

s.^ ____

TiO- _____

A1203—— -----

Cr203-~-~

FeO ——— -

MnO ————

MgO ————

PnO- Na2o- ——

Total——-

80BI15 

Gb

54.10

.21

2.08

n.d.

16.20

.90

25.90 

1.55

.04

100.98

80BI49 

Gbn

54.10

.20

1.66

n.d.

16.60

.77

25.90 

1.34

.04

100.61

80BI28 

Ol Hbl Gbn

52.90

.13

1.25

n.d.

23.70

.83

20.60 

1.47

.05

100.93

Kane Peak

81KP5A 81KP2A 

Hbl Phi Pd Hbl Phi Pd

54.90

.05

2.06

.47

8.05

.23

32.25 

.79

.02

98.79

55.29

.13

2.09

.43

8.02

.21

32.31 

.90

.01

99.39

Union Bay

87GH28A 

Gbn

51.03

.29

1.90

.03

22.03

.55

21.83 

1.07

.01

98.73

87GH50A 

BtGbn

50.51

.16

1.51

.00

27.52

1.00

17.07 

1.66

.03

99.46

Formula per 4 cations

Si

AlTM

Ti

Fe3* -—

R.2+ ____ .

Mn _______

JVlg

Na —————

Mg

(Mg+Fe'2+)

w t__. _

£„ _________

Fs

1.942

.058

.031

.006

.000

.018

.468

.027

1 187

.060

.003

.748

.032

.724

.244

1.951

.049

.022

.005

.000

.019

.482

.024

1.393

.052

.003

.743

.028

.722

.250

1.970

.030

.025

.004

.000

.001

.737

.026

1.144

.059

.004

.608

.031

.590

.380

1 32

.068

.018

.001

.013

.036

.201

.007

1.693

.030

.001

.894

.016

.879

.105

1.936

.064

.022

.003

.012

.024

.211

.006

1.687

.034

.001

.889

.018

.873

.109

1.923

.077

.008

.008

.001

.053

.642

.017

1.227

.043

.001

.657

.023

.641

.335

1.951

.049

.019

.005

.000

.023

.867

.033

.983

.069

.002

.532

.037

.512

.451

* Total iron as FeO; Fe3+ and Fe2+ in mineral formula caluclated from charge balance.

t Pyroxene components calculated according to the procedures of Lindsley and Andersen (1983).

Wollastonite

Enstatite Ferrosilite

Figure 14. Plot of compositions of clinopyroxene and 

orthopyroxene (circles) in ultramafic rocks and gabbro of Alaskantype intrusions, southeastern Alaska.

from progressively more hydrous melts characteristic of arc 

magmas (Murray, 1972; Conrad and Kay, 1984; Loucks, 

1990). The theory that the hydrous nature of the magma gave 

rise to the Alaskan-type ultramafic cumulates is supported by 

the common occurrence of phlogopite and hornblende in 

wehrlite and clinopyroxenite, and by hornblendite as part of 

the differentiation sequence. In contrast, hydrous minerals 

are not common in ultramafic cumulates of ophiolite sequences or other rift-related differentiation products 

(Himmelberg and Loney, 1980; Pallister and Hopson, 1981; 

Elthon and others, 1982; Komor and others, 1985; Loney and 

Himmelberg, 1989). The alumina content of orthopyroxene 

in the ultramafic rocks is not unusual (<2.09 weight percent); 

however, orthopyroxene is rare in the ultramafic rocks and is 

restricted to the earliest differentiates.
MINERAL CHEMISTRY 29

<D 

Q.

D)

1

CO

O

CM

2-

6

1 ' 1 ' 1

0.7 0.8 0.9 1.

Mg/(Mg+Fe2+)

Figure 15. Plot of weight percent A12O3 against Mg # [Mg/ 

(Mg+Fe2+)] of clinopyroxene (open squares) in ultramafic rocks 

and gabbro of Alaskan-type intrusions, southeastern Alaska. Field 

of Tonsina Complex of Burns (1985), from DeBari and Coleman 

(1989).

TiO , in weight percent

Figure 16. Plot of A11V content, expressed as a percentage of total 

tetrahedral Al, against TiO2 for clinopyroxene in clinopyroxenite 

and gabbro of Alaskan-type intrusions, southeastern Alaska. Field 

boundaries from LeBas (1962); trend arrows from Loucks (1990).

The esseneite component (CaFe3+AlSiO6) of 

clinopyroxene generally increases with the differentiation 

sequence of rocks. Clinopyroxene with substantial Fe3+ and 

esseneite component occurs in hornblende clinopyroxenite 

and magnetite clinopyroxenite at Douglas Island, Haines, 

Klukwan, Port Snettisham, and Union Bay (table 6). Experimental studies of Holloway and Burnham (1972) and arguments by Loucks (1990) demonstrate that when Fe2O3/FeO 

is buffered in the melt, increasing PH o causes crystallization 

of increasingly Fe3+-rich and Al-nch clinopyroxenes (as 

esseneite and possibly Ca-tschermakite components). The 

elevated PH o promotes oxidation of iron which enhances 

crystallization of Fe3+-rich esseneitic clinopyroxene. The 

occurrence of clinopyroxene that has the higher esseneite component in hornblende- and magnetite-rich clinopyroxenites 

is consistent with these arguments and suggests that the magmas that crystallized the Alaskan-type ultramafic rocks generally became more hydrous as fractionation proceeded. The 

absence of abundant magnetite and hornblende in the ultramafic rocks of the Blashke Islands and Kane Peak bodies, 

and the generally low esseneite component of clinopyroxene 

in these bodies, suggest that the magmas that crystallized these 

two bodies were probably less hydrous and less oxidizing 

than the magmas that crystallized the other bodies. The calcium-tschermakite component (CaTs) remains relatively low 

through the differentiation sequence (table 6).

The hornblendes in the Alaska-type ultramafic rocks 

and gabbros are mainly pargasite but also include pargasitic 

hornblende and tschermakitic hornblende (table 7; fig. 17). 

Experimental studies indicate that the upper stability limit of 

pargasite is 1,050°C between 8 and 16 kbar (Jenkins, 1983), 

which is higher than that of other amphiboles. The most Mgrich hornblendes (Mg # 0.970,0.981) occur as a postcumulus 

phase in the olivine-rich peridotite at Kane Peak. A gap between the Mg # of hornblende in olivine-rich peridotite and 

that of clinopyroxenite and hornblendite, where the range is 

from 0.893 to 0.602, implies no systematic relation between 

Mg # and modal mineralogy. The Mg # of hornblende in gabbro ranges from 0.777 to 0.594.

Phlogopite biotite is relatively common in the ultramafic rocks (table 8). The Mg # is 0.918 and 0.914 in wehrlite 

and olivine-rich peridotite at Dall Island and Kane Peak, respectively, and decreases systematically through clinopyroxenite to 0.572 in hornblendite. The most iron-rich biotite (Mg # 0.469) occurs in biotite gabbronorite at Union 

Bay.

Chromian spinel is common as an accessory mineral in 

dunite, wehrlite, and some olivine clinopyroxenites. Its general absence in clinopyroxenites, however, probably reflects 

a reaction between chromian spinel and clinopyroxene as 

suggested by Irvine (1967b). The major chemical variation 

of chromian spinel is a Cr # range that increases as the Fe2+ # 

increases (table 9, fig. 18). Excluding the Red Bluff Bay complex, the Fe3+ # ranges from 0.133 to 0.398, which is markedly higher than that for chromian spinels in ultramafic rocks
30 Table 6. Analyses of clinopyroxene in Alaskan-type ultramafic and mafic rocks, southeastern Alaska.

[Electron microprobe analyses (in weight percent) by G.R. Himmelberg. Blashke Islands and Salt Chuck analyses from Himmelberg and others (1986b) and Loney 

and Himmelberg (1992). Abbreviations given in table 2. Mg/(Mg+Fe2+), atomic ratio of normative silicates. -, not detected; n.d., not determined]

Blashke Islands

Sample No. — 

Rock type— -

SiOj —————

AI203- ——— 

CnCh ^A~rj___

FeO ________

Total-*-— _ ••-

80BI48 

Ol Cpxite

53.80 

.17 

1.91 

.32 

2.95 

.11 

17.50 

23.70 

.17

100.63

80BI43 

Du

54.80 

.06 

.91 

.09 

2.43 

.06 

17.40 

24.80 

.03

100.58

80BI10 

Du

53.40 

.03 

1.49 

.05 

2.64 

.05 

17.90 

24.80 

.06

100.42

80BI13 80BI47 80BI14 80BI28 80BI17 

Ol Cpxite Whr Ol Cpxite Ol Hbl Gbn Hbl Gb

54.30 53.20 52.30 53.20 

.13 .25 .26 .24 

1.61 2.87 2.87 2.12 

.30 n.d. .23 n.d. 

3.45 3.72 4.41 4.58 

.09 .09 .13 .12 

17.40 16.70 16.00 16.30 

23.60 23.40 23.70 23.40 

.17 .22 .18 .16

101.05 100.45 100.08 100.12

53.80 

.24 

1.86 

.30 

5.79 

.43 

14.70 

23.40 

.36

100.88

80BI15 

Gb

52.20 

.30 

2.24 

n.d. 

7.96 

.48 

14.50 

22.40 

.35

100.43

80BI49 

Gbn

52.10 

.50 

2.35 

n.d. 

8.47 

.41 

15.20 

21.20 

.37

100.60

80BI29 

Hbl Px Gb

53.00 

.25 

1.98 

n.d. 

7.76 

.56 

14.20 

22.30 

.48

100.53

Formula per 4 cations

AIIV

A1VI

Ti

ft...... ..........

ft*1---- ^

ft2+

Mffr --,-..,

,V|gr

Ca ——————

Mg 

(Mg+Fe2+) 

Wo— — — — — 

n_

Ac „

Es ——————

CaTs ————

Sample No. —— 

Rock type ——

2>lvl2""TM"TM""~""~""TM

A1203 ——— - 

Q203 ———— 

Ff£f ____

Na^o ____

Total- ———

1.941 

.059 

.023 

.005 

.009 

.030 

.059 

.003 

.942 

.917 

.012

.941 

.440 

.527 

.033 

.012 

.018 

.023

90GH6A 

Phi Whr

52.24 

.20 

2.83 

.67 

3.21 

.11 

16.32 

23.47 

.29

99.34

1.980 

.020 

.019 

.002 

.003 

.000 

.073 

.002 

.938 

.961 

.002

.927 

.471 

.491 

.038 

.000 

.000 

.017

Dall Island

90GH6C 

Bt Hbl Cpxite

51.63 

.30 

3.42 

.04 

5.50 

.13 

15.32 

23.47 

.26

100.05

1.926 

.064 

.000 

.001 

.001 

.000 

.080 

.002 

.963 

.960 

.004

.923 

.479 

.481 

.040 

.000 

.000 

.000

90GH6B 

Cpxile

51.05 

.39 

4.02

5.30 

.11 

14.71 

24.00 

.21

99.80

1.955 1.927 1.910 1.943 

.045 .073 .090 .057 

.023 .050 .034 .034 

.004 .007 .007 .007 

.009 n.d. .007 n.d. 

.018 .024 .047 .022 

.086 .088 .087 .118 

.003 .003 .004 .004 

.934 .903 .872 .888 

.912 .910 .929 .917 

.012 .015 .013 .011

.916 .911 .909 .882 

.443 .433 .433 .442 

.510 .516 .515 .492 

.047 .051 .052 .066 

.012 .015 .013 .011 

.006 .009 .035 .010 

.023 .050 .034 .034

Douglas Island

86DB69A 86DB64A 86DB68A 

Pig Cpxite Cpxite Hb Cpxite

47.50 49.00 50.60 

.92 .91 .68 

6.14 5.64 4.24

7.81 7.61 6.62 

.21 .19 .13 

12.70 12.60 14.00 

23.40 23.70 23.40 

.36 .43 .24

99.04 100.08 99.91

1.968 

.032 

.048 

.007 

.009 

.000 

.177 

.013 

.802 

.918 

.026

.819 

.444 

.456 

.101 

.000 

.000 

.023

1.925 

.075 

.022 

.008 

n.d. 

.061 

.184 

.015 

.798 

.886 

.025

.812 

.426 

.466 

.108 

.025 

.036 

.022

1.915 

.085 

.017 

.014 

n.d. 

.067 

.194 

.013 

.833 

.836 

.026

.811 

.403 

.485 

.113 

.026 

.040 

.017

1.953 

.047 

.039 

.007 

n.d. 

.028 

.212 

.017 

.781 

.882 

.034

.787 

.438 

.442 

.120 

.028 

.000 

.033

Haines

84GH53B 

Hbl Cpxite

48.69 

.82 

5.22

7.17 

.19 

13.58 

23.51 

.21

99.37

84GH53C 

Hbl Cpxite

50.04 

.62 

4.36

6.39 

.13 

14.58 

22.84 

.23

99.19

84GH54B 

Bt Cpxite

50.45 

.47 

3.35

6.61 

.16 

13.96 

23.71 

.33

99.04

84GH55B 

Hbl Cpxite

49.20 

.90 

5.62

6.78 

.12 

13.32 

24.13 

.20

100.27

Formula per 4 cations

A'jiv

A,V1 ____ 

"Tj_ ____

ft^iizr

j^2+ ____

Mcr..... ...... ,j

MB

(Mg+Fe2+) 

Wo" —— . ——

Es

CaTs ————

1.915 

.085 

.037 

.005 

.019 

.038 

.060 

.003 

.892 

.923 

.021

.937 

.435 

.529 

.036 

.021 

.018 

.037

1.892 

.108 

.040 

.008 

.001 

.069 

.099 

.004 

.837 

.923 

.019

.894 

.425 

.514 

.061 

.019 

.051 

.040

1.878 

.122 

.052 

.011 

.000 

.063 

.100 

.003 

.807 

.947 

.015

.890 

.431 

.506 

.063 

.015 

.048 

.052

1.777 1.816 1.870 

.223 .184 .130 

.048 .063 .055 

.026 .025 .019 

.000 .000 .000 

.148 .101 .054 

.096 .135 .151 

.007 .006 .004 

.709 .697 .772 

.939 .942 .928 

.026 .031 .017

.881 .838 .837 

.397 .420 .427 

.531 .486 .480 

.072 .094 .094 

.026 .031 .017 

.122 .070 .037 

.048 .063 .055

1.812 

.188 

.041 

.023 

.000 

.117 

.106 

.006 

.754 

.938 

.015

.876 

.406 

.521 

.074 

.015 

.102 

.041

1.857 

.143 

.047 

.017 

.000 

.078 

.121 

.004 

.807 

.909 

.017

.870 

.409 

.515 

.077 

.017 

.061 

.047

1.880 

.120 

.028 

.013 

.000 

.090 

.117 

.005 

.776 

.948 

.024

.869 

.439 

.487 

.073 

.024 

.066 

.028

1.815 

.185 

.060 

.025 

.000 

.089 

.120 

.004 

.733 

.955 

.014

.860 

.417 

.501 

.082 

.014 

.075 

.060

Footnotes at end of table.
MINERAL CHEMISTRY 

Table 6. Analyses of clinopyroxene in Alaskan-type ultramafic and mafic rocks, southeastern Alaska—Continued.

31

Haines-Continued

Sample No. —— 

Rock type — -

TiO2- ——— —

r 2r>3

§&==:

Total- — -----

84GH54A 

Bt Cpxile

49.62 

.97 

4.81

6.94 

.15 

13.47 

23.97 

.29

100.20

84GH55A 

Hbl Cpxite

50.23 

.37 

3.16

8.62 

.23 

12.53 

23.28 

.41

98.83

81SK043A 

Whr

53.85 

.13 

.93 

.68 

2.55 

.08 

17.56 

23.76 

.19

99 .74

Kane Peak

81SK046A 81KP22A 

Whr Cpxite

53.40 

.12 

.87 

.74 

2.52 

.07 

17.74 

23.45 

.17

99.06

52.92 

.22 

1.34 

.41 

3.73 

.14 

17.23 

22.78 

.26

99.03

Klukwan

81KP23A 81KP15A 81KP14A 84GH52D 

Ol Cpxite Cpxite Cpxite Mag Cpxite

53.57 52.23 51.01 

.18 .25 .44 

1.20 1.80 3.42 

0.45 .23 .02 

3.22 4.50 7.73 

.09 .11 .16 

17.23 16.42 14.70 

23.42 22.94 21.18 

.24 .29 .60

99.59 98 .77 99.26

51.21 

.39 

2.44

5.87 

.48 

15.50 

23.50 

.17

99.55

84GH52F 

Hbl Cpxite

48.00 

.89 

6.10 

.01 

6.69 

.07 

13.20 

24.00 

.21

99.14

Formula per 4 cations

Si A,iv __ __

A1VI. _____ 

Ti

Cr

R.3+

Mv

Mg 

(Mg+Fe2+) 

Wo'- _______ 

En

Ac

Es1.833 

.167 

.042 

.027 

.000 

.092 

.122 

.005 

.742 

.950 

.020

.858 

.428 

.491 

.081 

.020 

.072 

.042

1.894 

.106 

.034 

.011 

.000 

.081 

.191 

.007 

.705 

.942 

.030

.787 

.443 

.438 

.119 

.030 

.051 

.034

1 .961 

.039 

.001 

.004 

.020 

.024 

.053 

.002 

.954 

.928 

.013

.947 

.455 

.516 

.029 

.013 

.011 

.001

Port Snettisham

Sample No. -----

TiO2- ------

Cr203—— —— -

MgO — — -— 

CaO ————— 

Na2O- —————

Total--

87GH18A 

Cpxite

49.19 

.89 

4.90

6.00 

.13 

14.00 

23.81 

.23

99.15

87GH19A 

Cpxite

49.21 

.90 

4.84

6.04 

.13 

13.81 

24.15 

.20

99.28

87GH17A 

Cpxite

48.77 

.98 

5.40

7.12 

.16 

12.90 

23.95 

.28

99.57

1.956 

.037 

.000 

.003 

.021 

.021

.056 

.002 

.969 

.921 

.012

.946 

.451 

.519 

.030 

.012 

.009 

.000

1.944 

.056 

.002 

.006 

.012 

.047 

.067 

.004 

.944 

.898 

.018

.933 

.437

.526 

.038 

.018 

.029 

.002

1.957 1 

.043 

.008 

.005 

.013 

.029 

.069 

.003 

.939 

.918 

.017

.932 

.450 

.512 

.038 

.017 

.013 

.008

.930 1.893 

.070 .107 

.008 .042 

.007 .012 

.007 .000 

.062 .084 

.077 .156 

.003 .005 

.905 .814 

.909 .843 

.021 .043

.921 .839 

.437 .402 

.519 .502 

.044 .096 

.021 .043 

.041 .040 

.008 .042

Red Bluff Bay

90GH18A 

Whr

54.46 

.02

.89

.06 

18.22 

25.37 

.00

99.03

90GH15B 

Cpxite

53.82 

.03 

1.09 

.60 

2.05 

.10 

17.72 

23.87 

.14

99.41

90GH16B 

Cpxit

53.60

.08 

1.46 

.28 

2.96 

.15 

17.25 

23.88 

.09

99.76

1.891 

.106 

.000 

.011 

.000 

.096 

.085 

.015 

.853 

.931 

.012

.909 

.429 

.519 

.052 

.012 

.084 

.000

Salt Chuck

86GH23A 86GH34B 86GH20A 

Mag Cpxite Cpxite Mag Cpxite

48.60 48.82 

.53 .64 

4.78 4.65

6.91 7.37 

.16 .35 

14.15 14.16 

23.72 23.00 

.23 .35

99.08 99.32

49.45 

.42 

4.16

6.69

.14 

14.34 

23.53 

.27

99.00

1.789 

.211 

.057 

.025 

.000 

.120 

.089 

.002 

.734 

.959 

.015

.892 

.406 

.530 

.064 

.015 

.105 

.057

86GH25A 

Mag Cpxite

48.54 

.61 

5.28

7.15 

.22 

13.72 

23.53 

.30

99.35

86GH1B 

Mag Cpxite

48.88 

.61 

4.47

7.69 

.34 

13.75 

23.22 

.42

99.36

Formula per 4 cations

Si

AI«V ————

A, VI

Cr

CaMg 

(Mg+Fe'2+)

En

PC

Ac

1.828 

.172 

.043 

.025 

.000 

.096 

.090 

.004 

.776 

.949 

.017

.896 

.422 

.518 

.060 

.017 

.080 

.043

1.828 

.172 

.040 

.025 

.000 

.095 

.093 

.004 

.765 

.963 

.014

.892 

.428 

.510 

.062 

.014 

.081 

.040

1.816 

.184 

.053 

.028 

.000 

.097 

.125 

.005 

.716 

.956 

.020

.852 

.424 

.491 

.086 

.020 

.077 

.053

1.986 

.001 

.000 

.000 

.000 

.001 

.026 

.002 

.991 

.993 

.000

.974 

.496 

.491 

.013 

.000 

.001 

.000

1.962 

.038 

.009 

.001 

.017 

.019 

.043 

.003 

.964 

.934 

.010

.957 

.454 

.523 

.023 

.010 

.010 

.009

1.954 

.046 

.016 

.002 

.008 

.024 

.066 

.005 

.938 

.934 

.006

.934 

.449 

.514 

.036 

.006 

.018 

.016

1.808 1.813 

.192 .187 

.017 .017 

.015 .018 

.000 .000 

.162 .160 

.053 .069 

.005 .011 

.785 .784 

.946 .916 

.017 .025

.937 .919 

.400 .395 

.562 .556 

.038 .049 

.017 .025 

.146 .135 

.017 .017

1.839 

.161 

.022 

.012 

.000 

.135 

.073 

.004 

.796 

.939 

.019

.916 

.411 

.540 

.050 

.019 

.116 

.022

1.803 

.197 

.034 

.017 

.000 

.150 

.072 

.007 

.760 

.938 

.022

.913 

.398 

.550 

.052 

.022 

.129 

.034

1.818 

.182 

.014 

.017 

.000 

.165 

.074 

.011 

.763 

.926 

.030

.911 

.404 

.543 

.053 

.030 

.135 

.014

Footnotes at end of table.
32 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA 

Table 6. Analyses of clinopyroxene in Alaskan-type ultramafic and mafic rocks, southeastern Alaska—Continued.

Salt Chuck — Continued

Sample No. ------ 

Rock type -------

TiQ>- ___

A1203— -------

Pe0*- ____ ij=

86GH9B 

MagGb

49.64 

.59 

4.10

6.78

.37 

14.56 

22.74 

.34

86GH35A 86GH8A 

Mag Gb Mag Cpxite

49.96 

.44 

3.69

7.38

.41 

13.82 

22.71 

.71

49.53 

.62 

4.35

7.23

.34 

14.11 

23.25 

.36

86GH11A 86GH12A 

Mag Cpxite Mag Gb

48.51 

.59 

5.07 

.01

7.44

.24 

13.39 

23.34 

.38

48.29 

.60 

5.30

8.04

.24 

12.92 

23.55 

.46

86GH7A 

Gb

49.64 

.50 

3.61

7.27

0.42 

14.15 

22.96 

.38

86GH1A 

MagGb

49.27 

.67 

4.66

7.10

.33 

13.91 

23.05 

.38

86GH27A 

MagGb

50.09 

.55 

4.05 

.01

7.17

0.36 

14.30 

22.96 

.40

86GH3A 

MagGb

48.85 

.65 

4.89

7.49

.26 

13.44 

23.16 

.43

86GH30A 

MagGb

50.05 

.55 

3.46

7.33

.34 

14.38 

22.34 

.50

86GH3B 

Gb

50.02 

.58 

3.78

8.10

.60 

13.40 

22.04 

.58

Total———- 99.12 99.11 99.79 98.98 99.40 98.92 99.38 99.89 99.17 98.95 99.10

Formula per 4 cations

1.844

.156

.024

.017

.000

.124

.087

.012

.807

.906

.025

.903

.404

.538

.058

.025

.099

.024

1.859

.141

.021

.012

.000

.147

.082

.013

.767

.907

.051

.903

.420

.523

.056

.051

.096

.021

1.832

.168

.021

.017

.000

.138

.085

.011

.778

.923

.026

.901

.407

.534

.059

.026

.112

.021

1.811

.189

.035

.017

.000

.147

.085

.008

.746

.935

.027

.898

.404

.535

.061

.027

.120

.035

1.799

.201

.032

.017

.000

.168

.083

.007

.718

.941

.033

.897

.404

.535

.061

.033

.135

.032

1.853

.147

.012

.014

.000

.135

.092

.013

.788

.919

.027

.895

.414

.525

.061

.027

.108

.012

1.830

.170

.034

.019

.000

.127

.094

.010

.771

.918

.028

.892

.406

.529

.064

.028

.099

.034

1.850

.150

.026

.015

.000

.123

.099

.011

.788

.910

.029

.889

.409

.525

.066

.029

.094

.026

1.821

.179

.036

.018

.000

.138

.095

.008

.747

.926

.031

.887

.407

.526

.067

.031

.107

.036

1.865

.135

.017

.015

.000

.124

.105

.011

.799

.893

.036

.884

.412

.519

.068

.036

.087

.017

1.871

.129

.037

.016

.000

.102

.152

.019

.748

.884

.042

.831

.415

.486

.099

.042

.059

.037

Sukkwan Island

Sample No.- 

Rock type—

90GH9A 

Hbl Cpxite

Union Bay

87GH49A 87GH34A 87GH33A 87GH35A 87GH41A 878GH36A 87GH29A 87GH28A 87GH50A 

Ol Cpxite Whr Cpxite Cpxite Mag Cpxite 01 Cpxite Mag Cpxite Gbn Bt Gbn

Total———- 100.22

53.02

99.21

52.84 52.70 51.82 49.17 51.40 49.59

99.18 98.96 99.12 98.99 98.97 98.83

50.75

99.54

50.87

.11

1.26

.63

1.82

1.00

17.54

23.65

.19

.13

1.40

.62

2.21

.07

17.01

24.67

.23

.15

1.54

.53

3.04

.08

16.96

23.79

.17

.22

2.02

.46

4.17

.16

16.32

23.75

.20

.64

4.57

.00

6.22

.15

14.63

23.45

.16

.34

2.68

.14

6.30

.16

15.59

22.11

.26

.39

4.68

.

7.02

.21

14.51

22.18

.25

.56

3.13

.02

11.40

.36

13.92

18.98

.43

.24

2.05

-

13.09

.54

11.97

20.18

.35

99.28

Formula per 4 cations

CaTs——

1.847

.153

.066

.014

.008

.065

.108

.004

.794

.927

.015

.881

.408

.521

.071

.015

.051

.066

1.939

.055

.000

.003

.018

.044

.012

.031

.957

.928

.013

.988

.446

.547

.007

.013

.031

.000

1.934

.061

.000

.004

.018

.052

.015

.002

.929

.969

.016

.984

.466

.526

.009

.016

.036

.000

1.937

.063

.004

.004

.015

.047

.046

.002

.930

.938

.012

.952

.448

.526

.026

.012

.035

.004

1.909

.088

.000

.006

.013

.077

.052

.005

.897

.939

.014

.945

.439

.531

.031

.014

.062

.000

1.827

.173

.027

.018

.000

.121

.072

.005

.811

.935

.011

.918

.404

.547

.049

.011

.110

.027

1.907

.093

.024

.010

.004

.064

.132

.005

.863

.880

.018

.868

.412

.510

.078

.018

.045

.024

1.847

.153

.053

.011

.000

.097

.122

.007

.806

.887

.018

.868

.387

.532

.081

.018

.078

.053

1.903

.097

.042

.016

.001

.054

.304

.011

.778

.763

.031

.719

.365

.457

.178

.031

.023

.042

1.937

.063

.029

.007

.000

.046

.371

.018

.680

.824

.025

.647

.400

.388

.212

.025

.021

.029

* Total iron as FeO; Fe3+ and Fe2+ in mineral formula calculated from charge balance.

fPyroxene components calculated according to the procedures of Lindsley and Andersen (1983).
DISCUSSION 33

tL.tLV

2.00

1.75

1.50

1 .^O

1.00

0.75

0.50 

0.25

n nn .

Tschermakite

.j.

Tschermakitic hornblende

+

Magnesio-homblende

Actinolitic hornblende

Actinolite

++ + +

+ 1- + + + *

+ ±~ Pargasite

4-

r +

+Pargasitic hornblende

Edenitic hornblende

Edenite

Silicic edenite

0.0 0.2 0.4 0.6 

Cations in A-site

0.8 1.0

100

80-

COs.

601

k_ o,

O 40

20-

O

D

B

D

20 40 60 80 100

Fe2+/(Fe2++Mg)

^ Figure 17. Plot of A1IV against cations in A-site for 

hornblende in ultramafic rocks and gabbro of Alaskan-type 

intrusions, southeastern Alaska. Nomenclature from Leake (1978).

from other tectonomagmatic environments and is a characteristic originally pointed out by Irvine (1967b). The significantly lower Fe3"1" # of chromite in clinopyroxenite and dunite 

at Red Bluff Bay (0.080 and 0.126) supports the interpretation that this body is not an Alaskan-type ultramafic intrusion. Studies on Mg-Fe exchange between olivine and 

chromian spinel have shown that these minerals reequilibrate 

at subsolidus temperatures (Irvine, 1965; Evans and Frost, 

1975; Fabrics, 1979; Henry and Medaris, 1980; Engi, 1983). 

Subsolidus exchange of Mg-Fe will modify the Mg/(Mg+Fe2+) 

of both olivine and spinel, but the effect will be small for 

olivine and large for spinel because of the large difference in modal proportions of these two minerals in the rocks. 

Temperatures of equilibration calculated for 13 olivine and 

chromian spinel pairs in the Alaskan-type ultramafic rocks, 

using the calibration of Fabrics (1979), range from 470 to 

820°C, which is consistent with subsolidus reequilibration.

The chromian spinel compositions in the Alaskan-type 

ultramafic rocks are similar to those reported in arc-related 

cumulates and lavas (Conrad and Kay, 1984; Dick and Bullen, 

1984; DeBari and others, 1987; DeBari and Coleman, 1989).

Plagioclase is confined to the relatively minor gabbroic 

rocks of the Alaskan-type ultramafic-mafic intrusions. Analyses of plagioclase in representative Alaskan-type gabbros are 

given in table 10.

DISCUSSION

CRYSTALLIZATION CONDITIONS OF 

ULTRAMAFIC-MAFIC ROCKS

Several factors leave no doubt that the Alaskan-type 

ultramafic-mafic bodies formed from a basaltic magma by 

crystal fractionation and mineral concentration processes. 

These factors are (1) the sequence of appearance of primary 

minerals, (2) the common occurrence of essentially 

monomineralic and bimineralic rocks having chemistries that 

do not represent liquid compositions, (3) the rock REE patterns, (4) the mineral chemistry trends, and (5) the cumulus 

textures. The temperature, pressure, water content, and oxygen fugacity during crystallization of the Alaskan-type intrusions can be qualitatively estimated by comparing the natural

^ Figure 18. Plot of Cr # [Cr/(Cr+Al+Fe3+)] against Fe2+ # 

[Fe2V(Mg+Fe2*)] for chromian spinel in ultramafic rocks of Alaskantype intrusions, southeastern Alaska.
34 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA 

Table 7. Analyses of hornblende in Alaskan-type ultramafic and mafic rocks, southeastern Alaska.

[Electron microprobe analyses (in weight percent) by G.R. Himmelberg. Blashke Islands analyses from Himmelberg and others (1986b); sample 80BI19, g, green rim; 

b, brown core. Salt Chuck analyses from Loney and Himmelberg (1992). Abbreviations given in table 2. Mg/(Mg+Fe2++Mn), atomic ratio of normative silicates.]

Alava Bay

Sample No. — 

Rock type ——

Ti(>2 —————

/\i2v-»3 AllO-l ____ - 

PeO* ______ 

MnO

CaO —————

Na2O —— - —

"2*-*"

Total ____

90GH02 

Bt Hblite

41.51 

1.75 

13.28 

15.41 

.18 

10.71 

11.72 

2.34 

.92

97.82

80BII4 80BI49 

Ol Cpxite Gbn

45.10 43.60 

1.00 2.73 

12.20 11.70 

8.46 11.50 

.10 .23 

16.20 14.20 

12.50 12.00 

1.58 2.35 

.50 .00

97.64 98 ,31

80BI15 

Gb

43.10 

2.67 

13.20 

11.60 

.30 

13.60 

11.90 

2.52 

.40

99.29

Blashke Islands

80BI19b 

Gb

43.40 

2.57 

11.80 

13.60 

.42 

12.50 

11.20 

2.26 

.49

98.24

80DI29 

Hbl Px Gb

44.10 

2.19 

11.30 

12.50 

.38 

13.30 

11.80 

2.29 

.55

98.41

80BI19g 

Gb

50.80 

.88 

5.43 

13.50 

.52 

14.40 

11.80 

.99 

.50

98.82

80BI28 

Ol HblGbn

43.10 

2.16 

11.60 

15.60 

.26 

12.00 

11.60 

2.43 

.00

98.75

80BI17 

Hbl Gbn

45.30 

1.81 

9.46 

14.40 

.40 

12.70 

11.90 

1.44 

.72

98.13

Dall Island

90GH6B 90GH6C 

Cpxite Bt Hbl Cpxite

42.12 

1.32 

14.29 

8.92 

,09 

14.96 

12.24 

1.80 

1.72

97.47

41.72 

1.24 

14.24 

9.76 

.13 

14.67 

12.27 

1.77 

1.90

97.68

Formula per 13 cations exclusive of Ca, Na, K

Si ——————— A1iv

AI^ - -

Ti

Fe3*— --— 

R.2+. _____

Mn

M(T., j_ IVIg- ——

Na(B) ————

Na(A) ————

K , , MB

(Mg+Fe^++Mn)

6.166 

1.834 

.492 

.196 

.367 

1.548 

.023 

2.374 

1.867 

.133 

.542 

.174

.602

6.403 6 

1.597 1 

.445 

.107 

.604 

.401 

.012 

3.431 3 

1.904 1 

.096 

.339 

.091

.893

.266 

.734 

.249 

.296 

.537 

.846 

.028 

.044 

.850 

.150 

.506 

.000

.777

6.162 

1.838 

.388 

.288 

.451 

.936 

.036 

2.901 

1.825 

.175 

.525 

.073

.749

6.295 

1.705 

.313 

.281 

.618 

1.032 

.052 

2.704 

1.743 

.257 

.379 

.091

.714

Douglas Island

Sample No. — 

Rock type ——

TiC>2-TM ——— 

AI203~- —— - 

PeQ* ______ 

MnO ————— 

MnO— - GO ——— Na2O- —————

Total———

Si

A1IV

MTM

Ti

Fe3*- - - -

Fe2+~- -

Mn- •"- •"••->-

Mo ivjg,,,, — r-.,,.TM

Na(B) ————

Na(A) ———— 

j^

Me

(Mg+Fe'J++Mn)

86DB68A 

Hbl Cpxite

39.97 

2.13 

14.92 

10.46 

.08 

14.00 

12.99 

2.14 

1.92

98.61

5.847 

2.153 

.420 

.235 

.220 

1.060 

.010 

3.055 

2.039 

.000 

.607 

.359

.741

86DB69A 6DB64A 

Pig Cpxite Cpxite

39.77 39.97 

2.60 2.48 

14.03 13.45 

12.79 13.34 

.28 .18 

12.48 11.73 

12.62 12.36 

2.29 2.23 

1.77 1.61

98.61 97.33

5.887 6.007 

2.113 1.993 

.336 .390 

.289 .281 

.197 .097 

1.388 1.581

.035 .023 

2.755 2.629 

2.005 1.992 

.000 .008 

.658 .643 

.334 .309

.652 .621

84GH53C 

Hbl Cpxite

42.10 

1.89 

13.84 

8.93 

.10 

15.68 

12.74 

2.11 

1.04

98.41

Formula per

6.029 

1.971 

.365 

.204 

.507 

.562 

.012 

3.350 

1.957 

.043 

.543 

.190

.854

84GH53B 

Hbl Cpxite

41.11 

1.90 

14.06 

10.45 

.17 

14.23 

12.52 

2.25 

1.11

97.79

6.392 

1.608 

.323 

.239 

.391 

1.125 

.047 

2.875 

1.835 

.165 

.479 

.102

.711

Haines

84GH54B 

Bt Cpxite

39.38 

1.99 

13.66 

12.13 

.08 

13.73 

12.28 

2.31 

1.58

97.14

7.251 

.749 

.164 

.095 

.416 

1.196 

.063 

3.066 

1.807 

.193 

.081 

.091

.709

6.255 

1.745 

.240 

.236 

.736 

1.158 

.032 

2.598 

1.806 

.194 

.491 

.000

.686

6.606 

1.394 

.232 

.199 

.499 

1.258 

.049 

2.762 

1.862 

.138 

.269 

.134

.679

6.096 

1.904 

.535 

.144 

.455 

.625 

.011 

3.229 

1.901 

.099 

.406 

.318

.835

6.053 

1.947 

.490 

.135 

.517 

.667 

.015 

3.175 

1.909 

.091 

.408 

.352

.823

Kane Peak

84GH54A 

Bt Cpxite

39.68 

2.33 

14.25 

11.77 

.11 

13.35 

12.12 

1.98 

1.73

97.32

84GH55A 

Hbl Cpxite

39.23 

1.52 

13.54 

16.44 

.14 

10.67 

11.93 

1.80 

1.89

97.16

81KP5A 

Hbl Phi Pd

45.62 

.92 

11.35 

5.09 

.05 

18.34 

11.73 

2.33 

.84

96.27

81KP2A 

Hbl Phi Pd

46.19 

1.11 

11.37 

4.87 

.08 

18.58 

11.87 

2.41 

.84

97.30

1 3 cations exclusive of Ca, Na, K

5.989 

2.011 

.404 

.209 

.432 

.842 

.021 

3.092 

1.957 

.043 

.594 

.206

.782

5.839 

2.161 

.227 

.222 

.620 

.885 

.010 

3.036 

1.953 

.047 

.618 

.299

.772

5.856 

2.144 

.335 

.259 

.560 

.893 

.014 

2.939 

1.919 

.081 

.486 

.326

.764

5.921 

2.079 

.331 

.173 

.647 

1.429

.018 

2.402 

1.932 

.068 

.459 

.364

.624

6.492 

1.508 

.396 

.099 

.537 

.069 

.006 

3.893 

1.791 

.209 

.434 

.153

.981

6.508 

1.492 

.396 

.118 

.463 

.110 

.009 

3.904 

1.794 

.206 

.453 

.151

.970

Footnote at end of table.
DISCUSSION 

Table 7. Analyses of hornblende in Alaskan-type ultramafic and mafic rocks, southeastern Alaska—Continued.

35

Kane Peak— Continued Klukwan Port Snettisham Salt Chuck Sukkwan Island

Sample No. — 

Rock type ——

SiO2 —————

TJQ- _________

AI203- ——— - 

Pe0* _______ 

MnO~

MoO. .....

Total ————

81KP1D 

Diorite

43.99 

1.80 

11.79 

13.47 

.20 

12.44 

10.31 

1.61 

1.05

96.64

81KP1C 

Hblite

42.40 

1.80 

13.92 

14.14 

.26 

11.13 

11.72 

2.07 

1.05

98.46

84GH52D 84GH52F 

Mag Cpxite Hbl Cpxite

42.86 

1.43 

13.70 

8.02 

.09 

15.95 

13.22 

1.89 

.85

98.01

40.77 

1.85 

15.09 

11.07 

.14 

13.88 

12.88 

1.97 

1.42

99.07

87GH18A 

Cpxite

40.48 

2.03 

14.83 

9.84 

.10 

15.18 

12.72 

1.97 

1.95

99.10

87GH19A 87GH17A 

Cpxite Cpxite .

40.32 

2.08 

14.81 

11.44 

.10 

14.10 

12.60 

1.73 

2.16

99.32

38.79 

2.47 

15.05 

14.05 

.16 

12.09 

12.43 

1.91 

1.84

98.77

86GH9B 

MagGb

40.04 

2.15 

13.19 

13.00 

.25 

12.97 

12.31 

2.56 

1.31

97.79

90GH9A 

Hbl Cpxite

42.82 

1.88 

12.56 

13.36 

.20 

12.44 

11.91 

1.71 

.92

97.80

Formula per 13 cations exclusive of Ca, Na, K

AlTM-

AliVI

Fe3*--

(Mg+Fe^+Mn)

6.409

1.591

.434

.198

.890

.751

.024

2.702

1.612

.388

.065

.194

.777

6.207

1.793

.609

.199

.324

1.407

.032

2.429

1.840

.160

.427

.196

.628

6.145

1.855

.461

.154

.336

.626

.011

3.411

2.034

.000

.526

.156

.843

5.887

2.113

.455

.201

.450

.887

.017

2.990

1.996

.004

.548

.262

.768

5.818

2.182

.331

.220

.582

.601

.012

3.254

1.961

.039

.511

.358

.841

5.822

2.178

.344

.226

.595

.788

.012

3.036

1.952

.048

.437

.398

.792

5.711

2.289

.323

.273

.603

1.128

.019

2.654

1.963

.037

0.508

.346

.698

5.939

2.061

.245

.241

.429

1.185

.031

2.869

1.959

.041

.697

.249

0.702

6.258

1.742

.422

.207

.514

1.120

.025

2.712

1.867

.133

.352

.172

.703

Union Bay

Sample No.— 87GH29A 87GH47A 87GH40A 87GH44A 

Rock type—-- Mag Hbl Cpxit Cpxite Hblite Hbl Gb

TiOj ——— 

AI203-~ 

FeO*-

MnO ——

MgO ——

CaO ———

Na2O ——

K2O ——— 

Total —

—— 1.73 

—— 14.42 

o Qn

—— .12

—— 14.36

—— 12.21

—— 2.07

—— 1.10

—— 97.44

41.46 

1.77 

14.61 

11.69 

.23

13.35

12.28

1.96

.94

98.29

40.48 

1.63 

14.15 

13.40 

.17

11.91

12.27

2.23

1.20

97.41

42.50 

1.53 

12.32 

15.99 

.46

10.71

12.00

1.63

1.31

98.43

Formula per 13 cations exclusive of Ca, Na, K

Si

A11V

AIVI

Ti ———

Fe3*

Fe2+

Mn ———

Mg 

Ca ———

Na(B)~ 

Na(A) — 

K

—— 6.025

1.975

.490

.523

.678

——— .015 ——— 3.106

—— 1.900

——— .100 

——— .482 

9na

5.995 

2.005 

.485 

.193 

.601 

.813 

.028 

2.879 

1.905 

.095 

.455

174

6.014 

1.986 

.493 

.182 

.350 

1.316 

.021 

2.639 

1.955 

.045 

.597

997

6.285 

1.715 

.432 

.170 

.423 

1.554 

.058 

2.362 

1.903 

.097 

.370

9.17

Me

r- 2-K (Mg+Fe-^+Mn) .818 .774 .664 .594

* Total iron as FeO; Fe3+ and Fe2* calculated from 

charge balance.

mineral assemblages and crystallization sequence to products of hydrous melting and crystallization experiments using natural basaltic compositions. These factors are discussed 

in detail below.

The sequence of appearance of cumulus phases and 

the mineral chemical depletion trends indicate the following 

cumulate sequence for the Alaskan-type ultramafic rocks:

Olivine+chromian spinel (dunite)

Olivine+clinopyroxene±chromian spinekfcphlogopite 

(wehrlite, olivine clinopyroxenite)

Clinopyroxene±magnetite(clinopyroxenite)

Clinopyroxene+hornblende±phlogopite±magnetite(hornblende-biotite clinopyroxenite)

Hornblende±magnetite(hornblendite).

The occurrence of gabbro at the Blashke Islands, Union 

Bay, and Salt Chuck indicates evolved crystallization of the 

cumulus assemblage:

Plagioclase+clinopyroxene±orthopyroxene± magnetite. 

The crystallization order appropriate to the Alaskantype cumulate sequence of rocks is therefore olivine + minor chromite, clinopyroxene, magnetite, hornblende, 

plagioclase ± orthopyroxene. This crystallization sequence, 

with the exception of orthopyroxene, has been duplicated by 

experimental studies of water-saturated and -undersaturated 

basaltic melts at an oxygen fugacity near that of the nickelnickel oxide (NNO) buffer (Holloway and Burnham 1972;
36 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

Table 8. Analyses of biotite in Alaskan-type ultramafic and mafic rocks, southeastern Alaska.

[Electron microprobe analyses (in weight percent) by G.R. Himmelberg. Abbreviations given in table 2. Mg/(Mg+Fe), atomic ratio of normative silicates. 

-, not detected.]

Alava Bay

Sample No. — - 

Rock type ------

HOv

A'2v3 --------- 

FeO* _____

MnO —————

r-lb

Na2O —————

90GH02 

Bt Hblite

37.70 

1.38 

15.27 

17.73 

.07 

13.31 

.02 

.11 

9.02

94.61

Dall Island

90GH06A 90GH06C 84GH54A 

Phi Whr Bt Hbl Cpxite Bt Cpxite

39.61 

.74 

15.81 

3.78 

.07 

23.86 

.05 

.73 

8.14

92.79

38.38 

1.38 

16.54 

9.38 

.07 

20.12 

.01 

.34 

9.22

95.44

37.21 

2.67 

17.12 

10.07 

.09 

18.96

.47 

9.04

95.62

Haines

84GH54B 

Bt Cpxite

37.33 

2.49 

16.91 

10.64 

.07 

18.77

.46 

9.00

95.67

84GH55A 

Hbl Cpxite

36.16 

2.02 

16.60 

16.71 

.28 

14.64

.14 

9.16

95.68

81KP2At 

Hbl Phi Pd

40.25 

.37 

14.98 

4.30 

.02 

25.68 

.03 

.75 

9.05

95.43

Kane Peak

81KPI5A 81KP14A 

Cpxite Cpxite

39.54 

1.86 

15.22 

6.85 

.06 

21.64

.52 

9.23

94.92

37.44 

4.21 

16.16 

11.88 

.03 

16.37

.41 

9.69

96.19

Cations per 1 1 oxygens

Si

AjIV __ 

A1V1 _____ 

Ti

Fe ——————————

CaKin

Mg 

(Mg+Fe)

2.859 

1.141

.223 

.079 

1.124 

.005 

1.504 

.002 

.017 

.872

.572

Kane Peak —

Sample No. -— 

Rock type ----- -

SJO2 ————— 

TiO2- -— — ~ 

A1_P3- ——— 

FeO* ————— 

MnO — — —— .

Na2O ————— 

K2O ——————

Total-- —— —

SiA1IV __ 

Al^-

Ti

Fe

Mn ——————

Mp IVIg_

Ca^

Na ———————

Mg 

(Mg+Fe)

81KPIB 

Diorite

38.31 

2.06 

17.84 

13.85 

.32 

14.04

.36 

9.24

96.03

2.804 

1.196

.343

.113 

.848 

.020 

1.532 

.000 

.052 

.862

.644

2.847 

1.153 

.187 

.040 

.227 

.004 

2.557 

.004 

.102 

.746

.918

Continued

8IKP1C 

Hblite

37.18 

1.99 

17.56 

16.79 

.15 

12.57

.19 

9.76

96.18

2.769 

1.231 

.310 

.111 

1.046 

.009 

1.395 

.000 

.027 

.927

.572

2.774 

1.226 

.183 

.075 

.567 

.004 

2.168 

.001 

.047 

.850

.793

2.699 

1.301 

.162 

.145 

.611 

.005 

2.049 

.000 

.067 

.836

.770

2.712 

1.288 

.160 

.136 

.646 

.004 

2.032 

.000 

.065 

.834

.759

Port Snettisham

87GHI8A 

Cpxite

37.63 

1.87 

17.75 

8.34 

.06 

21.12 

.01 

.47 

9.99

97.24

2.674 

1.326 

.161 

.100 

.496 

.003 

2.237 

.001 

.065 

.906

.819

87GH19A 

Cpxite

36.95 

2.01 

17.35 

10.67 

.09 

18.94

.17 

10.14

96.32

Cations per 1 1

2.684 

1.316 

.169 

.110 

.648 

.006 

2.051 

.000 

.023 

.939

.760

86GH8A 

Mag Cpxite

36.64 

4.03 

16.55 

10.99 

.17 

17.59 

.04 

.62 

8.56

95.18

oxygens

2.683 

1.317 

.111 

.222 

.673 

.011 

1.919 

.003 

.088 

.799

.740

2.712 

1.288 

.178 

.114 

1.048 

.017 

1.636 

.000 

.020 

.876

.610

Salt Chuck

86GH9B 

MagGb

35.76 

3.70 

16.93 

12.06 

.19 

17.47 

.15 

.39 

7.90

94.53

2.642 

1.358 

.117 

.205 

.745 

.012 

1.924 

.012 

.056 

.744

.721

2.839 

1.161 

.084 

.020 

.254 

.001 

2.700 

.002 

.103 

.814

.914

86GHI2A 

MagGb

36.26 

3.58 

17.10 

13.04 

.20 

16.00 

.10 

.27 

7.72

94.26

2.689 

1.311 

.183 

.200 

.809 

.013 

1.768 

.008 

.039 

.730

.686

2.839 

1.161 

.127 

.100 

.411 

.004 

2.316 

.000 

.072 

.845

.849

Union Bay

87GH50A 

BtGbn

36.43 

4.27 

15.50 

20.22 

.16 

10.02 

.01 

.08 

9.60

96.29

2.766 

1.234 

.153 

.244 

1.284 

.010 

1.134 

.001 

.011 

.930

.469

2.733 

1.267 

.122 

.231 

.725 

.002 

1.780 

.000 

.058 

.960

.711

t NiO=0.16. 

* Total iron as FeO.
DISCUSSION 37

Table 9. Analyses of chromian spinel in Alaskan-type ultramafic and mafic rocks, southeastern Alaska.

[Electron microprobe analyses (in weight percent) by G.R. Himmelberg. Blashke Islands analyses from Himmelberg and others (1986b). Abbreviations given in table 2. 

Cr/(Cr+Al), Mg/(Mg+Fe2+), Fe3+/(Cr+Al+Fe3+), atomic ratios of normative silicates, n.d., not determined.]

Blashke Islands

Sample No. — - 

Rock type ------

SiO2 —————

Ti02 ——— —— 

A1203 ———— -

Pr_rU *- ______ r2lJ3 

FeO*

80B137 

Du

n.d. 

0.38 

12.00 

45.80 

13.18 

17.73 

1.26 

9.93

100.27

80BI5 

Du

n.d. 

0.44 

11.90 

43.60 

14.91 

18.97 

1.40 

9.03

100.25

80BI6 

Du

n.d. 

0.57 

11.20 

40.20 

18.02 

20.96 

1.29 

7.71

99.96

80BI43 

Du

n.d. 

0.44 

11.40 

38.90 

19.95 

21.13 

1.27 

7.72

100.81

80BI10 

Du

n.d. 

0.60 

20.00 

31.60 

17.82 

20.35 

1.03 

9.38

100.78

80BI12 

Du

n.d. 

0.96 

18.60 

30.10 

19.79 

21.77 

1.23 

8.38

100.83

Dall Island

80BI44 80BII3 

Whr Ol Cpxite

n.d. n.d. 

0.83 0.58 

18.70 16.40 

28.80 33.40 

20.62 17.25 

22.42 24.66 

1.12 1.19 

7.85 5.76

100.34 99.24

90GH6A 

Whr

0.03 

1.03 

10.92 

29.02 

27.99 

22.73 

3.30 

5.52

100.52

Kane Peak

81SK046A 

Whr

0.03 

.64 

7.35 

49.20 

11.77 

22.63 

.48 

6.64

98.76

81SK048A 

Du

0.02 

.89 

8.00 

46.05 

14.63 

22.34 

.48 

7.18

99.59

Formula normalized to 3 cations

Si

Ti

Al ———

Fe3*

R.2+ _____ 

Mn ——————

Mg ——————— 

Cr

(Cr+AI) 

Mg 

(Mg+Fe'z+)

Fe3+

(Cr+Al+Fe3+)

n.d. 

0.009 

.465 

1.190 

.326 

.488 

.035 

.487

.719 

.499 

.165

n.d. 

0.011 

.465 

1.142 

.372 

.526 

.039 

.446

.711 

.459 

.188

n.d. 

0.014 

.444 

1.070 

.457 

.591 

.037 

.387

.707 

.396

.232

n.d. 

0.011 

.449 

1.027 

.502 

.591 

.036 

.384

.696 

.394 

.254

n.d. 

0.014 

.750 

.795 

.427 

.542 

.028 

.445

.515 

.451 

.216

n.d. 

0.023 

.706 

.767 

.480 

.587 

.034 

.403

.521 

.407 

.246

Kane Peak — Continued

Sample No. -----

cjoA1203 ————— 

0203- -——--—

Pp_rw reTJ3 _ -—— ~ _

FcO*

Tniil

81SK043A 

Whr

0.03 

.71 

8.77 

48.65 

10.64 

23.53 

.51 

6.32

99.15

81KP7A 

Du

0.03 

.36 

9.22 

45.83 

12.52 

24.92 

.60 

5.03

98.50

81KP5A 

Hbl Phi Pd

0.03 

.58 

9.24 

44.92 

11.60 

27.10 

.81 

3.44

97.72

81KP17A 

Whr

0.03 

.61 

10.34 

47.46 

10.13 

24.68 

.61 

5.68

99.54

81SK045A 

Du

0.01 

1.54 

10.50 

38.02 

17.56 

26.74 

.54 

4.92

99.83

81KP23A 

Ol Cpxite

0.01 

2.82 

8.01 

28.47 

28.01 

28.67 

.43 

4.30

100.72

n.d. n.d. 

0.020 0.015 

.716 .649 

.740 .886 

.504 .436 

.609 .693 

.031 .034 

.380 .288

.508 .577 

.384 .294 

.257 .221

0.00 

.03 

.44 

.78 

.72 

.65 

.10 

.28

.642 

.309 

.371

Red Bluff Bay

90GH15B 

Cpxite

0.00 

.20 

16.18 

46.23 

6.41 

24.05 

.67 

6.59

100.33

90GH16A 

Du

0.00 

.34 

22.01 

36.65 

10.55 

22.13 

.60 

8.66

100.94

87GH34A 

Whr

0.00 

.79 

8.73 

42.76 

18.02 

22.52 

.46 

7.23

100.51

0.001 

.017 

.301 

1.354 

.309 

.660 

.014 

.344

.818 

.343 

.157

Union Bay

87GH27B 

Du

0.00 

.68 

8.99 

43.85 

16.23 

22.06 

.48 

7.31

99.60

0.001 

.023 

.324 

1.250 

.378 

.643 

.014 

.367

.794 

.363 

.194

87GH27A 

Du

0.00 

1.10 

8.40 

36.89 

21.50 

25.93 

.46 

4.82

99.10

Formula normalized to 3 cations

Si

Ti

AlCr

R.3+ _____

Fe2+ - -

MnK«n !Vig .............

Cr

(Cr+Al) 

Mg 

(Mg+Fe'z+)

Fe3+

(Cr+Al+Fe3+)

0.001 

.018 

.356 

1.328 

.277 

.680 

.015 

.325

.789 

.323 

.141

0.001 

.009 

.380 

1.269 

.330 

.730 

.018 

.262

.770 

.264

.167

0.001 

.016 

.388 

1.267 

.311 

.809 

.024 

.183

.765 

.184

.158

0.001 

.016 

.418 

1.287 

.262 

.709 

.018 

.290

.755 

.291

.133

0.000 

.040 

.427 

1.037 

.456 

.772 

.016 

.253

.708 

.247 

.237

0.000 

.074 

.329 

.786 

.736 

.838 

.013 

.224

.705 

.211 

.398

0.000 

.005 

.628 

1.204 

.159 

.663 

.019 

.323

.657 

.328

.080

0.000 

.008 

.819 

.915 

.251 

.585 

.016 

.407

.528 

.411

.126

0.000 

.020 

.350 

1.149 

.461 

.641 

.013 

.366

.767 

.364

.235

0.000 

.018 

.362 

1.185 

.418 

.631 

.014 

.373

.768 

.371 

.212

0.000 

.029 

.348 

1.025 

.569 

.763 

.014 

.253

.747 

.249

.293

* Total iron was determined and FeO and ^203 was calculated from stoicliiometry.
38 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

Table 10. Analyses of plagioclase in Blashke Islands Alaskan-type gabbro, 

southeastern Alaska.

[Electron microprobe analyses (in weight percent) from Himmelberg and others (1986b).

Sample No. — - 

Rock type ------

PeO* ______ 

KoO—

Total- ———

Si

ft—

£=

Or

80BI49 

Gbn

48.10 

33.60 

n.d. 

n.d. 

17.20 

2.03 

.04

100.97

2.186 

1.800 

n.d. 

n.d. 

.838 

.179

82'.2 

17.6

.2

80BI15 

Gb

47.10 

33.50 

.40 

.06 

17.40 

2.10 

.10

100.66

2.158 

1.809 

.015 

.004 

.854 

.187 

.006 

81.6 

17.8 

.6

80BI17 80BI28 80BI29 

Hbl Gb Ol Hbl Gbn Hbl Px Gb

48.70 

32.40 

.43 

.06 

16.00 

2.82 

.12

50.20 

32.60 

n.d. 

n.d. 

15.10 

3.16 

.06

100.53 101.12

Cations per 8

2.225 

1.745 

.016 

.004 

.783 

.250 

.007 

75.3 

24.0 

.7

oxygens

2.265 

1.734 

n.d. 

n.d. 

.730 

.276 

.003 

72.3 

27.4 

.3

49.40 

31.90 

.33 

.07 

15.30 

3.26 

.04

100.30

2.256 

1.717 

.013 

.005 

.749 

.289 

.002 

72.0 

27.8 

.2

80BI19 

Gb

53.80 

29.20 

.14 

.04 

11.60 

5.37 

.18

100.33

2.430 

1.554 

.005 

.003 

.561 

.470 

.010 

53.9 

45.1 

1.0

* Total iron as FeO

Helz, 1973). The abundance of magnetite and hornblende 

indicates that the magma from which the ultramafic rocks 

crystallized was substantially rich in Fe2O3 and H2O, at least 

by the time magnetite and hornblende crystallized. The occurrence of cumulus magnetite as the oxide phase, crystallizing after clinopyroxene but before hornblende, suggests 

that the oxidation conditions of the magma at the time of 

crystallization were at least as high as the NNO buffer 

(Holloway and Burnham, 1972; Helz, 1973). At lower oxidizing conditions, the fayalite-magnetite-quartz (FMQ) buffer 

ilmenite is the near-liquidus phase, and its upper stability 

limit is lower than that of hornblende. At conditions of the 

hematite-magnetite (HM) buffer, Fe-Ti oxide phases are 

among the earliest to crystallize, but they include abundant 

titanohematite (Helz, 1973), which was not observed in the 

Alaskan-type intrusions. The substantial esseneite component of clinopyroxene in most magnetite clinopyroxenites 

and hornblende clinopyroxenites also suggests a relatively 

high oxygen fugacity during crystallization of these rocks. 

Variation in esseneite component of clinopyroxene and the 

near absence of magnetite and hornblende in the ultramafic 

rocks at the Blashke Islands and Kane Peak, however, indicate that the oxygen fugacity and water content probably 

varied among the different intrusions. Similar oxidizing 

conditions near the NNO buffer were reported for arc-basalt 

ultramafic xenoliths that have mineral assemblages similar 

to Alaskan-type ultramafic rocks (Arculus and Wills, 1980; 

Conrad and Kay, 1984).

The crystallization sequence of most of the Alaskantype intrusions suggests that the ultramafic cumulates crystallized under pressures greater than about 3 kbar, but the 

upper pressure limit is not well constrained. Experimental 

studies of hydrous basalts at the NNO buffer have shown that 

at moderate to high pressures hornblende crystallizes at a temperature substantially higher than that at which plagioclase 

crystallizes; however, at low pressures (2-3 kbar) the upper 

stability of plagioclase and hornblende are relatively close, 

and below about 2.5 kbar plagioclase crystallizes before hornblende (Holloway and Burnham, 1972). The crystallization 

sequence of the Salt Chuck intrusion, where plagioclase follows magnetite, and hornblende is nearly absent, indicates 

that the Salt Chuck body crystallized under a pressure of 2 

kbar or less (Loney and Himmelberg, 1992).

Proposed mineral composition barometers do not further constrain the pressure of crystallization. A steep increase 

in A12O3 of clinopyroxene with differentiation (a decrease in 

Mg #) has been argued to indicate a high-pressure origin 

(Medaris, 1972; Asahina and Komatsu, 1979; Yokoyama, 

1980; Ishiwatari, 1985; Ishizuka, 1985; DeBari and Coleman, 

1989). Clinopyroxene in the Alaskan-type cumulates shows 

a moderately steep increase of A12O3 with differentiation (fig. 

15); however, in this case, the accommodation of Al in pyroxene is more likely related to crystallization of clinopyroxene from progressively more hydrous melts characteristic of arc magmas (Murray, 1972; Conrad and Kay, 1984; 

Loucks, 1990). The partitioning of Al between octahedral and
DISCUSSION 39

tetrahedral sites in clinopyroxene (Green and Ringwood, 

1967; Aoki and Kushiro, 1968) also does not indicate highpressure crystallization of the Alaskan-type ultramafic 

clinopyroxenes. Chromian spinel has also been suggested as 

a geobarometer because the composition becomes more Alrich as the pressure increases (Green and others, 1971; Jaques 

and Green, 1980). Allan and others (1988), however, have 

shown that spinel compositions are also strongly dependent 

on small variations in host-liquid composition and thus their 

use as a geobarometer is limited.

The metamorphic grade of the country rock surrounding the Alaskan-type bodies indicates that the magma chambers in which the ultramafic rocks accumulated were at relatively shallow crustal levels. Mineral assemblages indicate 

the grade of metamorphism to be greenschist or subgreenschist 

facies (Brew and others, 1992). Irvine (1967a, 1974), Findlay 

(1969), James (1971), and Himmelberg and others (1986b) 

attribute the zoned character of the bodies to diapiric 

reemplacement following crystallization and accumulation in 

a deeper magma chamber. As discussed below, however, we 

believe the zoned character developed by flow differentiation rather than by diapiric reemplacement Even if diapiric 

reemplacement did occur, Irvine (1974) suggests that the upward movement of the dense ultramafic cumulates would have 

been limited to only a few kilometers at the very most; thus 

the metamorphic grade of the country rocks would still be a 

reasonable indicator of depth of crystallization.

On the basis of geobarometry of pelitic schist pendants, 

emplacement depth of the Baranof Lake pluton, which intrudes the Red Bluff Bay ultramafic body, might have been 

about 18 to 20 km (Himmelberg, unpub. data). However, 

Loney and others (1975) interpret the Red Bluff Bay body to 

have been tectonically emplaced at its present structural level; 

thus, it may have crystallized at a deeper crustal level. We 

note again, however, that the Red Bluff Bay body may not be 

an Alaskan-type complex, and its depth of crystallization may 

not be appropriate to constrain that of the Alaskan-type intrusions.

The temperature of crystallization of the cumulus assemblages is best estimated by comparison to the hydrous 

basalt melting and crystallization experiments referred to 

above. The liquidus temperature is not determined; however, 

at 5 kbar and the NNO buffer, the upper stability of magnetite is 1,085°C and the upper stability of hornblende is 

1,025°C. These conditions suggest that the magnetite and 

hornblende clinopyroxenites and hornblendites crystallized 

at about this temperature range (Holloway and Burnham, 

1972; Helz, 1973). On the basis of the upper stability of plagioclase, the gabbros would have begun crystallizing at about 

925°C, and crystallization would have been complete at about 

815°C (Holloway and Burnham, 1972). The presence of 

pargasite as a postcumulus phase in the olivine-rich peridotite at Kane Peak suggests that the cumulus minerals in these 

rocks crystallized above about 1,025°C. These temperatures 

increase with increase of pressure.

We conclude that the Alaskan-type ultramafic rocks 

crystallized from hydrous basaltic magmas at shallow crustal 

depths, probably in the range of 6 to 18 km. Water content 

and oxygen fugacity was somewhat variable among the different bodies, but the latter was probably above the NNO 

buffer and below the HM buffer. Crystallization temperatures 

ranged from above 1,025°C to about 815°C.

NATURE OF THE PARENT MAGMA

The Alaskan-type complexes have long been recognized 

as a distinct class of ultramafic-mafic intrusions (Noble and 

Taylor, 1960; Taylor and Noble, 1960; Irvine 1974), and the 

nature of the parental magma has long been debated. No 

chilled margins representing the parental magma have been 

found, so the original melt composition can only be inferred 

from consideration of cumulate sequences and from rock and 

mineral chemistry relative to experimental and theoretical 

studies. James (1971), Murray (1972), Himmelberg and others (1986b), and more recently Loucks (1990) and Loney and 

Himmelberg (1992) have argued that at least some of the Alaskan-type ultramafic rocks were fractionated from subalkaline 

orthopyroxene-normative island-arc basaltic parental magmas 

with the resultant production of residual basaltic and andesitic liquids. Subalkaline island-arc basaltic parental magmas 

for Alaskan-type ultramafic rocks were also implied by 

Conrad and Kay (1984) and DeBari and others (1987), who 

equated xenoliths in Aleutian island-arc volcanic rocks with 

Alaskan-type ultramafic rocks. Irvine (1967a, 1974), on the 

other hand, argued that the Alaskan-type ultramafic rocks were 

fractionated from high-calcium, high-magnesium, alkaline 

ultramafic parental magmas with the resulting production of 

residual, critically undersaturated, alkali basalts.

Our data and that of others clearly indicate that the 

magma that crystallized these ultramafic rocks must have been 

substantially rich in Fe2O3 by the time magnetite crystallized 

and that the abundance of hornblende, and commonly biotite, 

indicates a substantial H2O content. Irvine (1974) argued that 

the parental magma must have been extremely rich in MgO 

and CaO to crystallize so much olivine and clinopyroxene. 

He further argued that, in those rocks where postcumulus minerals are abundant, the bulk rock composition should qualitatively reflect the composition of the parent magma. Alaskantype ultramafic rocks with abundant postcumulus hornblende 

typically have nepheline in the norm. On the basis of experimentally determined systems, Irvine (1974) then showed that 

a critically undersaturated (nepheline-normative) magma 

would crystallize to yield the cumulate sequence of ultramafic rocks and account for the abundance of magnetite typical 

of Alaskan-type ultramafic rocks. Loucks (1990), however, 

pointed out that the experimental studies of Bowen (1928), 

Helz (1973), and Wones (1979) all showed that hornblende 

precipitated from orthopyroxene- or quartz-normative melts 

is generally nepheline-normative. Thus hornblende- or biotite-
40 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

bearing cumulates that crystallized from saturated hydrous 

magmas will commonly be feldspathoid-normative, and a 

nepheline-normative magma is not required.

Our preferred interpretation is that the mineral assemblages, the crystallization sequence, and the rock and mineral chemistry all indicate fractionation from a silica-saturated, hypersthene-normative parental magma similar to those 

that yield island-arc basalts. Although modal orthopyroxene 

is not common in many Alaskan-type ultramafic rocks, it does 

occur in trace amounts in wehrlite and olivine clinopyroxenite 

at the Blashke Islands and is common as a postcumulus phase 

along with hornblende and phlogopite in some peridotites at 

Kane Peak. Most importantly, as discussed above, the ultramafic rock mineral assemblages and crystallization sequence 

are duplicated by crystallization experiments of hydrous silicasaturated basaltic melts having an oxygen fugacity near that 

of the NNO buffer (Holloway and Burnham, 1972; Helz, 

1973). Hornblende in the hornblende clinopyroxenites is typically feldspathoid normative, as noted in the experimental 

studies of Helz (1973), and the clinopyroxene compositions 

change from hypersthene normative to feldspathoid-normative with fractionation. The clinopyroxenes become 

feldspathoid normative with fractionation, owing to an increase in the esseneite component as a result of the hydrous 

oxidizing nature of the magma. Loucks (1990) argued that in 

a hydrous and oxidizing basaltic magma the activity of 

enstatite component would be depressed and the activities of 

the aluminous pyroxene components in the melt would be 

raised, promoting crystallization of olivine and clinopyroxene 

and yielding wehrlite and olivine clinopyroxenite in place of 

gabbronorite in early cumulate sequences. This crystallization order has the added consequence of enhancing the alumina and silica content of progressive residual liquids thus 

leading to crystallization of high-alumina basalts common to 

an arc crust (Loucks, 1990). The increasing alumina content 

of clinopyroxene with fractionation, the steep trend of the 

Al:Ti ratio in clinopyroxene in Alaskan-type bodies (fig. 16) 

and other rocks from island-arc environments (Loucks, 1990), 

and the crystallization of hornblende support this interpretation. Fractionation of ultramafic cumulates has been proposed 

by Conrad and Kay (1984) and by Kay and Kay (1985a, b) as 

the mechanism of deriving high-alumina basalt magmas.

The more evolved rocks associated with the Tulameen 

complex in British Columbia range from gabbro to syenitic 

(Findlay, 1969). In the Sierra Nevada and Klamath Mountains, California, however, James (1971) and Snoke and others (1981, 1982) documented a genetic relation between ultramafic bodies having Alaskan-type characteristics and mafic rocks ranging from olivine gabbro, through gabbronorite, 

to diorite, tonalite, and granodiorite. Irvine (1974) questioned, 

however, whether such occurrences are truly Alaskan-type 

complexes because of their obvious fractionation from saturated magmas and his conviction that the Alaskan-type bodies were derived from undersaturated magmas. Gabbros are 

also associated with classic Alaskan-type complexes at Duke

Island, Blashke Islands, Union Bay, and Salt Chuck. As 

pointed out above, at Duke Island the gabbros are obviously 

older than the ultramafic rocks and need not be considered in 

the petrogenesis of that complex. At Union Bay the mafic 

rocks are dominantly gabbronorite and form an outermost 

zone about the ultramafic rocks. Biotite and hornblende from 

the gabbroic rocks yield K/Ar ages of 101 to 110 Ma (M.A. 

Lanphere, written commun., 1990), and similar ages of Alaskan-type ultramafic rocks (Lanphere and Eberlein, 1966; M.A. 

Lanphere, written commun., 1990) suggest that the gabbroic 

rocks and ultramafic rocks are genetically related and were 

fractionated from a subalkaline, saturated parental magma. 

At the Blashke Islands, two-pyroxene gabbros also form an 

outermost zone of the ultramafic complex. These gabbroic 

rocks grade from pyroxene gabbro at the contact with olivine 

clinopyroxenite to hornblende gabbro near the periphery. 

These gabbroic rocks have not been dated by isotopic methods, but Himmelberg and others (1986b) argued that they are 

crystallization products of the same magma that had fractionated the ultramafic rocks. At Salt Chuck, magnetite 

clinopyroxenite and magnetite gabbro represent a continuous sequence, which Loney and Himmelberg (1992) interpreted to have been fractionated from hydrous, saturated basaltic parental magma.

Irvine (1967a,1974), Murray (1972), and Himmelberg 

and others (1986b) all proposed that the Alaskan-type ultramafic complexes accumulated in subvolcanic magma chambers. Murray (1972) and Irvine (1974) tried to draw correlations between the Alaskan-type ultramafic complexes and 

associated volcanic rocks as evidence for parental magma 

type, however these arguments remain inconclusive. In southeastern Alaska the volcanic rocks of the Gravina-Nutzotin 

belt of Berg and others (1972) form a discontinuous belt nearly 

coincident with the Klukwan-Duke mafic-ultramafic belt. 

Berg and others (1972) indicated that these volcanic rocks 

were dominantly andesite. However, studies by Irvine (1973) 

and Ford and Brew (1988) indicate that these volcanic rocks, 

at least in the vicinity of Juneau, Alaska, are basaltic and include high-potassium basalt. The generally accepted age of 

these volcanic rocks is Jurassic to Cretaceous (Buddington 

and Chapin, 1929; Lathram and others 1965; Berg and others, 1972), but recent studies by H. Cohen (written commun., 

1992) suggest that they are mid-Cretaceous in age. Irvine 

(1973; 1974) argued that they are possibly related as part of 

the same petrologic province and could have been derived 

from the same alkaline parental magma type. Mortimer (1986) 

and Nixon and Rublee (1988) have suggested that the 

Tulameen Alaskan-type complex is coeval with the volcanic 

rocks of the Upper Triassic Nicola Group in British Columbia, Canada. These volcanic rocks are also island-arc related, 

clinopyroxene-phyric, calc-alkaline to shoshonitic lavas 

(Mortimer, 1986). Similarly, Alaskan-type complexes in New 

South Wales are part of a belt of Ordovician shoshonitic volcanic and associated intrusive rocks (Derrick, 1991). Remarkably similar compositions of clinopyroxene phenocrysts in
INTRUSIVE MECHANISM AND ZONAL STRUCTURE 41

the Douglas Island Volcanics (Himmelberg, unpub. data) and 

clinopyroxene in the ultramafic complexes support the argument that these two rock groups may be genetically related. 

As discussed above, however, these pyroxene compositions 

are compatible with crystallization from a hydrous basaltic 

magma. Thus, as mentioned above, arguments about parental magma type based on possible coeval volcanic rock compositions remain inconclusive.

The older 400- to 440-Ma Alaskan-type complexes in 

southern southeastern Alaska were emplaced into a volcanicarc environment (Gehrels and Saleeby, 1987). Volcanic rocks 

of the Descon Formation consist of basalts and andesites and 

were extruded during the Early Ordovician through the Early 

Silurian (Gehrels and Saleeby, 1987). The Salt Chuck body 

is intruded into the Descon Formation (Loney and 

Himmelberg, 1992) so, as with the younger Alaskan-type 

complexes and associated volcanics, there is the possibility 

that the exposed volcanic rocks may be somewhat older than 

the ultramafic-mafic complex.

Our current preferred interpretation is that all of the 

Alaskan-type ultramafic complexes are cumulates that fractionated from a hydrous subalkaline island-arc basaltic 

magma. Himmelberg and others (1986b), in contrast, suggested that all the Alaskan-type complexes may not have been 

derived from the same parent magma type. Reexamination 

of all the characteristics of all the bodies, including REE patterns, indicates that they are so similar that a common parent 

magma composition seems most reasonable. The Mg-rich 

olivine in Alaskan-type dunite and wehrlite suggests that the 

parental melt was an unfractionated mantle-derived melt. The 

high Cr # of the chromian spinel suggests equilibrium of the 

magma with a mantle peridotite that underwent a high degree of melting (Dick and Bullen, 1984). Although the exact 

composition of the primary melt is uncertain, we suggest it 

was possibly similar to the hydrous olivine basalt primary 

magma proposed for the Aleutian island-arc lavas (Perfit and 

others, 1980; Kay and others, 1982; Nye and Reid, 1986; 

Conrad and Kay, 1984; DeBari and others, 1987). This suggestion is based on the similarities of mineralogy, texture, 

and rock and mineral chemistry of the Alaskan-type ultramafic rocks and gabbros and Aleutian island-arc xenoliths and 

plutonic gabbros described by Perfit and others (1980), Kay 

and others (1983), Conrad and Kay (1984), and DeBari and 

others (1987). The 87Sr/86Sr ratio in Alaskan-type ultramafic 

rocks ranges from 0.702 to 0.705 (Lanphere, 1968), which is 

within the range for Aleutian island-arc plutonic and volcanic rocks and xenoliths (Kay and others, 1986; 1990). At Salt 

Chuck the magnetite clinopyroxenite is intruded by a diabase 

dike that has an appropriate chemical composition, Mg#, and 

redox state to represent a plausible parental liquid for the Salt 

Chuck mineral assemblages (Loney and Himmelberg, 1992). 

The diabase dike is hypersthene-normative and somewhat 

similar in chemical composition to the 1921 Kilauea olivine 

tholeiite used in the hydrous experiments of Holloway and 

Burnham (1972) and Helz (1973).

INTRUSIVE MECHANISM AND 

ZONAL STRUCTURE

Researchers generally agree that Alaskan-type ultramafic complexes originated by fractional crystallization and accumulation in subvolcanic magma chambers or feeder conduits (Irvine, 1967a, 1974; Murray, 1972; Himmelberg and 

others (1986b). However, there are differences of opinion on 

the primary processes responsible for the magmatic differentiation and zonal structure. Murray (1972) proposed that the 

zoned Alaskan-type ultramafic intrusions originated by crystal fractionation and flow differentiation of basaltic magma 

in the feeder pipes of volcanoes, whereas Irvine (1974) proposed that in most cases the zonal structure is a result of diapiric reemplacement of stratiform sequences of cumulates.

On the basis of field relations and heat-flow models, 

Irvine (1974) argued that flow differentiation would not be 

an effective process for producing the zonal structures in intrusions as large as the Duke Island, Union Bay, and Tulameen 

bodies. He believed that any effect of flow differentiation 

would be obliterated by convection and crystal settling. Irvine 

proposed instead that the sequence of ultramafic rocks in Alaskan-type complexes accumulated in subvolcanic magma 

chambers by crystal fractionation and crystal settling to form 

rudely stratiform complexes and that the zonal structure was 

produced by later diapiric reemplacement caused by tectonic 

compression. Irvine (1974) explains the absence of widespread deformation to the presence of intercumulus liquid 

during diapiric emplacement, which is represented by 

undeformed postcumulus minerals.

The mechanism of flow differentiation is a well-established hydraulic process that has been studied since 1825 for 

many compound liquids, such as printing ink, coal slurries, 

and melted chocolate. Flow differentiation was first considered as a magmatic process to explain structures in the Labrador Trough of Canada (Baragar, 1960), the Skye picritic 

dikes and sills of Scotland (Bhattacharji and Smith, 1964), 

and the Muskox intrusion of Canada (Simkin 1967). 

Bhattacharji and Smith (1964) showed experimentally that 

the type of monomineralic segregation and cryptic zonation 

found in picritic dikes of Skye, and also in the feeder dike of 

the Muskox intrusion, could be produced by magmatic flowage differentiation. In the Muskox intrusion only the vertical 

feeder dike shows zonation; the main part of the body, the 

subhorizontal central-layered series, is typical of layered cumulates developed largely by fractional crystallization and 

crystal settling (Smith 1962; Irvine and Smith, 1967).

Murray (1972) attributed the zonal structure of Alaskan-type ultramafic rocks to the flow differentiation model 

as developed by Bhattacharji and Smith (1964) and 

Bhattacharji (1967a). According to this model, during flow 

through a conduit, segregation takes place by particles in liquid moving away from the walls toward the central axis and 

then parallel to the axis. Thus in a vertical conduit containing
42 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

rising mafic magma, early-formed Mg-rich olivine crystals 

move from the wall toward the center where they form an 

olivine-rich rock. The olivine is followed by pyroxene, plagioclase, and so on, as crystallization proceeds. Because of 

fractional crystallization, individual minerals would also show 

characteristic trends in chemical composition. As upward 

movement of the magma and core continues, further crystallization and flow differentiation would develop a zonal sequence of rocks similar to that of the Alaskan-type ultramafic complexes. Postintrusion crystal settling is minor because 

of the high viscosity of the concentration (Bhattacharji and 

Smith, 1964; Shaw, 1965). Murray (1972) suggested that the 

gabbros commonly associated with, and in some cases apparently intruded by, the ultramafic rocks could represent 

solidification of derived magmas that were later intruded by 

the continually rising and crystallizing ultramafic core. 

Bhattacharji (1967a, b) also showed, through a carefully 

scaled experiment, that the zoned configuration created in a 

feeder conduit can continue into a sill. The resulting zoned 

geometry is remarkably similar to the interpretation shown 

in figure 4 for the Union Bay intrusion as constructed by 

Ruckmick and Noble (1959, pi. 4) and supported by our work.

The extent of flow differentiation in basaltic magma 

feeder conduits, dikes, and sills is dependent on the velocity 

of flow and viscosity of the magma. If velocity decreases or 

viscosity increases to critical values, flow differentiation decreases and other processes such as gravity settling or current modifications may prevail (Simkin, 1967; Bhattacharji, 

1967a, b). Texturally, on the basis of the present data, it does 

not seem possible to distinguish gravity and current-modified gravity cumulates from products of flow differentiation. 

The main evidence for flow differentiation is on a larger scale, 

namely the symmetrical arrangement of layering in pipes, 

dikes, and sills, such as at Blashke Islands, Union Bay (fig. 

4), and at Skye (Bhattacharji and Smith, 1964), which cannot 

be explained by gravity settling.

The Alaskan-type bodies display both gradational and 

sharp, in some cases intrusive, contacts between the various 

rock types. Both Murray (1972) and Irvine (1974) argued that 

these relations can be explained by flow differentiation as the 

major process and by diapiric reemplacement. Other than at 

Duke Island, possible large Alaskan-type in situ cumulus 

bodies are lacking in southeastern Alaska. Although we have 

no direct evidence to document the exact nature of emplacement and development of zonal structure in the Alaskan-type 

ultramafic bodies, we prefer the flow differentiation interpretation proposed by Murray (1972). The common symmetrical nature of the distribution of rock types for the size of most 

of the intrusions is compatible with the flow differentiation 

model. The olivine petrofabrics of the Union Bay body are 

attributed to regional tectonic recrystallization. The data suggest that the Kane Peak body was possibly intruded during 

that regional deformation event, but the olivine microfabric 

retains an igneous signature. The ultramafic body at the 

Blashke Islands shows no evidence of being involved in deformation of the western metamorphic belt. Both the Kane

Peak and Blashke Islands intrusions appear to be subvertical 

cylindrical structures that contain subvertical olivine 

microfabrics suggestive of subvertical magmatic flow. Some 

of these features could be produced by diapiric emplacement 

as well as by flow differentiation, but there is little data on 

the details of magmatic diapiric emplacement and how to distinguish it from flow differentiation intrusion.

In keeping with the flow differentiation proposal, we 

attribute the variations in character of the various Alaskantype intrusions to different degrees of interaction of flow, gravity settling, and current activity. The Duke Island body shows 

little evidence of flow differentiation. Magma was emplaced 

into a relatively large chamber in which the velocity decreased 

as the chamber filled, thus, gravity settling along with density-current activity prevailed, as in the main part of the 

Muskox intrusion. The Union Bay body illustrates a vertical 

zoned conduit that extends into a moderately sized, zoned, 

nappe-like sill. Open folding about subvertical northweststriking axial planes related to regional metamorphism deform the nappe-like structure, but it seems likely that the nappe 

itself, with its symmetrical intricate zonation, was caused by 

the flow differentiation discussed above. The Kane Peak body, 

although disturbed by later granitic intrusion, retains its igneous character. Because of the subvertical macroscopic and 

microscopic structural orientation in both the Blashke Islands 

and Kane Peak bodies, we believe they represent sections 

through zoned subvertical conduits. According to Robertson 

(1956), the Klukwan intrusion is a subvertical mass and probably represents a zoned conduit or dike, but details are lacking. Most of the other bodies are generally too small and 

poorly exposed to yield diagnostic information.

Gabbro and ultramafic rock relations also differ somewhat in the different intrusions. At the Blashke Islands the 

prominent flow banding in the peripheral gabbro indicates 

that it moved upward with the ultramafic rocks, as part of the 

flow-differentiation process. At Union Bay, however, the gabbro could represent a derived liquid that crystallized at a level 

above the ultramafic rocks and was subsequently intruded by 

the continuing upward-moving ultramafic core, as proposed 

in the model of Murray (1972). At Salt Chuck the gradational 

cumulus relations between the ultramafic rocks and the gabbro, and the absence of zonation, suggest crystal settling in a 

small static magma chamber.

CONCLUSIONS

Our study reaffirms that those bodies referred to as Alaskan-type complexes are a distinct class of ultramafic-mafic 

intrusions. They are characterized primarily by their tectonic 

setting, rock types, rock chemistry including REE, and mineral chemistry. The Alaskan-type complexes are cumulates 

formed from a basaltic magma by crystal-fractionation and 

mineral-concentration processes. They are characterized by 

Mg-rich olivine, diopsidic to augitic clinopyroxene, magne-
REFERENCES CITED 43

tite, and hornblende. Clinopyroxene in the later differentiates (magnetite clinopyroxenite and hornblende clinopyroxenite) generally have a substantial esseneite component 

which is a result of the hydrous, oxidizing nature of the 

magma. Orthopyroxene and plagioclase are rare in the ultramafic rocks but are locally common in associated gabbros. 

Some of the larger complexes are crudely zoned, with dunite 

in the core and wehrlite, olivine clinopyroxenite, magnetite 

clinopyroxenite, hornblende clinopyroxenite, and in some 

cases hornblendite and gabbro occurring successively outward. However, zoning is not universal and is not a criterion 

for recognition of Alaskan-type intrusions. Many of the bodies consist of only hornblende clinopyroxenite or hornblendite. 

Irvine (1974) implied that the term "Alaskan-type complex" 

should be restricted to those bodies that fractionated from an 

alkaline ultrabasic liquid. We disagree strongly because an 

argument can be made that most bodies recognized as Alaskan-type complexes were fractionated from a hydrous, saturated basaltic magma, and we do not believe the definition of 

an Alaskan-type complex should be restricted on the basis of 

parental magma composition at this time.

The Alaskan-type complexes in southeastern Alaska fall 

into two distinct age groups—about 400 to 440 Ma and 100 

to 118 Ma. Both groups occur in island-arc petrologic-tectonic environments, and their distribution suggests an eastward migration of arc-basaltic magmatism. The intrusion of 

the Alaskan-type complexes is part of a long-lived magmatic, 

metamorphic, and tectonic evolution of the convergent continental margin of southeastern Alaska and western Canada. 

The similarity of rock and mineral chemistry, including chondrite-normalized REE patterns for individual rock types from 

the different bodies, suggests that the parent magmas and conditions of crystallization for all the bodies were similar. The 

mineral chemistry and phase equilibria of the ultramafic rocks 

suggest that they crystallized and accumulated in magma 

chambers at depths ranging from about 6 to 18 km. We found 

no evidence that suggests deep crustal levels (30-35 km) as 

proposed for other island-arc ultramafic-mafic bodies and xenoliths associated with island-arc basalts. Although not conclusive, most of the field, petrographic, and chemical characteristics suggest to us that most of the bodies in southeastern 

Alaska crystallized from hydrous island-arc-basalt primary 

magmas. Furthermore, the petrographic and chemical similarities of the rocks in the Alaskan-type complexes and the 

Aleutian island-arc xenoliths and plutonic gabbros suggest 

that the parental magmas for the Alaskan-type ultramaficmafic bodies were similar to the parental magmas proposed 

for island-arc basalts and andesites.

Irvine (1974) proposed that the zonal structure is a result of diapiric reemplacement of stratiform sequences of 

cumulates. We found no evidence for diapiric reemplacement. 

Instead, we believe that the zonal structure is a result of crystal fractionation and flow differentiation in subvolcanic conduits and sills, which is consistent with the proposal of Murray 

(1972). We attribute the variations in character of the various 

Alaskan-type complexes to the size of the bodies, which affected whether flow differentiation or gravity settling was 

dominant, and to the level of exposure.

Although the Red Bluff Bay intrusion on Baranof Island has been included by some as an Alaskan-type complex 

and is discussed in this report, evidence suggests that it should 

not be classified as an Alaskan-type complex.

REFERENCES CITED

Albee, A.L., and Ray, Lily, 1970, Correction factors for electron 

probe microanalysis of silicates, oxides, carbonates, phosphates, 

and sulfates: Analytical Chemistry, v. 42, p. 1408-1414.

Allan, J.F., Sack, R.O., and Batiza, Rodey, 1988, Cr-rich spinels as 

petrogenetic indicators: MORB-type lavas from the Lamont 

seamount chain, eastern Pacific: American Mineralogist, v. 73, 

p. 741-753.

Aoki, Ken-ichiro, and Kushiro, Ikuo, 1968, Some clinopyroxenes 

from ultramafic inclusions in Dreiser Weiher, Eifel: Contributions to Mineralogy and Petrology, v. 18, p. 326-337.

Arculus, R.J., and Wills, K.J.A., 1980, The petrology of plutonic 

blocks and inclusions from the Lesser Antilles island arc: 

Journal of Petrology, v. 21, p. 743-799.

Asahina, T, and Komatsu, M., 1979, The Horokanai ophiolitic complex in the Kamuikotan tectonic belt, Hokkaido, Japan: Geological Society of Japan Journal, v. 85, no. 6, p. 317-330.

Av6 Lallemant, H.G., 1975, Mechanisms of preferred orientations 

of olivine in tectonic peridotite: Geology, v. 3, p. 653-656.

Baragar, W.R.A., 1960, Petrology of basaltic rocks in part of the 

Labrador trough: Geological Society of America Bulletin, v. 

71, p. 1589-1644.

Bence, A.E., and Albee, A.L., 1968, Empirical correction factors for 

the electron microanalysis of silicates and oxides: Journal of 

Geology, v.76, p. 382^03.

Berg, H.C., Jones, D.L., and Coney, P.J., 1978, Map showing preCenozoic tectonostratigraphic terranes of southeastern Alaska 

and adjacent areas: U.S. Geological Survey Open-File Report 

78-1085,2 sheets, scale 1:1,000,000.

Berg, H.C., Jones, D.L., and Richter, D.H., 1972, Gravina-Nutzotin 

belt—Tectonic significance of an upper Mesozoic sedimentary 

and volcanic sequence in southern and southeastern Alaska, in 

Geological Survey Research 1972: U.S. Geological Survey 

Professional Paper 800-D, p. D1-D24.

Bhattacharji, Somdev, 1967a, Mechanics of flow differentiation in 

ultramafic and mafic sills: Journal of Geology, v. 75, p. 101- 

112.

Bhattacharji, Somdev, 1967b, Scale model experiments on flowage 

differentiation in sills, Part 3.IV in Wyllie, P.I, ed., Ultramafic 

and related rocks: New York, John Wiley, p. 69-70 .

Bhattacharji, Somdev, and Smith, C.H., 1964, Flowage differentiation: Science, v. 145, p. 150-153.

Bowen, N.L., 1928, The evolution of the igneous rocks: Princeton, 

N. J., Princeton University Press, 334 p.

Brew, D.A., 1990, Plate-tectonic setting of Glacier Bay National 

Park and Preserve and Admiralty Island National Monument, 

southeastern Alaska, in Milner, A.M. ed., Second Glacier Bay 

Science Symposium Proceedings: U.S. National Park Service 

Science Publications Office, Atlanta, Ga. p. 1-5.

Brew, D.A., and Ford, A.B., 1984, Tectonostratigraphic terranes in
44 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

the Coast plutonic-metamorphic complex, southeastern Alaska, 

in Reed, K.M., and Bartsch-Winkler, Susan, eds., The United 

States Geological Survey in Alaska: accomplishments during 

1982: U.S. Geological Survey Circular 939, p. 90-93.

Brew, D.A., and Ford, A.B., 1985, Southeastern Alaska coincident 

zone, in Bartsch-Winkler, Susan, ed., The United States Geological Survey in Alaska: accomplishments during 1984: U.S. 

Geological Survey Circular 967, p. 82-86.

Brew, D.A., Ford, A.B., and Himmelberg, G.R., 1989, Evolution of 

the western part of the Coast plutonic—metamorphic complex, 

southeastern Alaska, U.S.A.: a summary, in Daly, J.S., Cliff, 

R.A., and Yardley, B.W.D., eds., Evolution of metamorphic 

belts: London, Geological Society Special Publication 43, p. 

447^52.

Brew, D.A., and Grybeck, D.J., 1984, Geology of the Tracy ArmFords Terror Wilderness Study Area and vicinity, Alaska, in 

Mineral resources of the Tracy Arm-Fords Terror Wilderness 

Study Area and vicinity, Alaska: U.S. Geological Survey Bulletin 1525-A, p. 19-52.

Brew, D.A., Himmelberg, G.R., Ford, A.B., and Jachens, R.C., 1987, 

Ultramafic and mafic sills in the vicinity of the Treadwell 

gold deposits, Douglas Island, southeastern Alaska, in 

Hamilton, T.D., and Galloway, J.P., eds., Geologic studies in 

Alaska by the U.S. Geological Survey during 1986: U.S. 

Geological Survey Circular 998, p. 119-123.

Brew, D.A., Himmelberg, G.R., Loney, R.A., and Ford, A.B., 1992, 

Distribution and characteristics of metamorphic belts in the 

south-eastern Alaska part of the North American Cordillera: 

Journal of Metamorphic Geology, v. 10, p. 465-482.

Brew, D.A., Karl, S.M., Barnes, D.F., Jachens, R.C., Ford, A.B., 

and Horner, Robert, 1991, A northern Cordilleran ocean-continent transect: Sitka Sound, Alaska, to Atlin Lake, British Columbia: Canadian Journal of Earth Sciences, v. 28, 840-853.

Brew, D.A., and Morrell, R.P, 1983, Intrusive rocks and plutonic 

belts of southeastern Alaska, U.S.A., in Roddick, J.A., ed., 

Circum-Pacific plutonic terranes: Geological Society of 

America Memoir 159, p. 171-193.

Brew, D.A., Ovenshine, A.T., Karl, S.M., and Hunt, S.J., 1984, Preliminary reconnaissance geologic map of the Petersburg and 

parts of the Port Alexander and Sumdum 1:250,000 quadrangles, southeastern Alaska: U.S. Geological Survey OpenFile Report 84-405, 43 p.

Brothers, R.N., 1959, Flow orientation of olivine: American Journal of Science, v. 257, p. 574-584.

Brothers, R.N., 1964, Petrofabric analyses of Rhum and Skaergaard 

layered rocks: Journal of Petrology, v. 5, p. 255-274.

Buddington, A.F., and Chapin, Theodore, 1929, Geology and mineral deposits of southeastern, Alaska: U.S. Geological Survey 

Bulletin 800, 398 p.

Burns, L.E., 1985, The Border Ranges ultramafic and mafic complex, south-central Alaska: cumulate fractionates and islandarc volcanics: Canadian Journal of Earth Sciences, v. 22, p. 

1020-1038.

Burrell, P.D., 1984, Cretaceous plutonic rocks, Mitkof and Kupreanof 

Islands, Petersburg quadrangle, southeast Alaska, in Coonrad, 

W.L., and Elliot, R.L., eds., The United States Geological Survey in Alaska: accomplishments during 1981: U.S. Geological 

Survey Circular 868, p. 124-126.

Carter, N.L. , and Ave' Lallemant, H.G., 1970, High temperature 

flow of dunite and peridotite: Geological Society of America 

Bulletin, v. 81, p. 2181-2202.

Clark, Thomas., 1980, Petrology of the Turnagain ultramafic complex, northwestern British Columbia: Canadian Journal of Earth 

Sciences, v.17, p. 744-757.

Coleman, R.G., 1977, Ophiolites; ancient oceanic lithosphere?; Vol. 

12 of Minerals and rocks: New York, Springer-Verlag, 229 p.

Coleman, R.G., and Keith, T.E., 1971, A chemical study of 

serpentinization—Burro Mountain, California: Journal of Petrology, v. 12, p. 311-328.

Conrad, W.K., and Kay, R.W., 1984, Ultramafic and mafic inclusions from Adak Island: crystallization history, and implications for the nature of primary magmas and crustal evolution 

in the Aleutian arc: Journal of Petrology, v. 25, p. 88-125.

DeBari, S.M., and Coleman, R.G., 1989, Examination of the deep 

levels of an island arc: evidence from the Tonsina ultramaficmafic assemblage, Tonsina, Alaska: Journal of Geophysical 

Research, v. 94-B, p. 4373-4391.

DeBari, S.M., Kay, S.M., and Kay, R.W., 1987, Ultramafic xenoliths from Adagdak volcano, Adak, Aleutian Islands, Alaska: 

deformed igneous cumulates from the Moho of an island arc: 

Journal of Geology, v. 95, p. 329-341.

Den Tex, E. ,1969, Origin of ultramafic rocks, their tectonic setting 

and history: a contribution to the discussion of the paper "The 

origin of ultramafic and ultrabasic rocks" by PJ. Wyllie: 

Tectonophysics, v. 7, p. 457-488.

Derrick, G.M., 1991, Geology and economic potential of the Tout 

Complex, NSW, in Elliott, S.J., and Martin, A.R., eds., Geology and mineralization of the Fifield platinum province, New 

South Wales—Sixth International Platinum Symposium, Perth, 

Western Australia, Guidebook for the pre-symposium field excursion: Perth, Western Australia, Geological Society of Australia, p. 24-34.

Dick, H.J.B., and Bullen, Thomas, 1984, Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas: Contributions to Mineralogy and Petrology, v. 86, p. 54-76.

Douglass, S.L., and Brew, D.A., 1985, Polymetamorphism in the 

eastern Petersburg quadrangle, southeastern Alaska, in BartschWinkler, Susan, ed., The United States Geological Survey in 

Alaska: accomplishments during 1984: U.S. Geological Survey Circular 967, p. 89-92.

Elliott, S.J., and Martin, A.R., 1991, Geology and mineralization of 

the Fifield platinum province, New South Wales—Sixth International Platinum Symposium, Perth, Western Australia, Guidebook for the pre-symposium field excursion: Perth, Western 

Australia, Geological Society of Australia, 42 p.

Elthon, Don., Casey, J.F., and Komor, S., 1982, Mineral chemistry 

of ultramafic cumulates from the North Arm Mountain massif 

of the Bay of Islands ophiolite: evidence from high-pressure 

crystal fractionation of oceanic basalts: Journal of Geophysical Research, v. 87-B, p. 8717-8734.

Engi, Martin, 1983, Equilibria involving Al-Cr spinel: Mg-Fe exchange with olivine. Experiments, thermodynamic analysis, and 

consequences for geothermometry: American Journal of Science, v. 283-A, p. 29-71.

Evans, B.W., and Frost, B.R., 1975, Chrome-spinel in progressive 

metamorphism—A preliminary analysis: Geochimica et 

Cosmochimica Acta, v. 39, p. 959-972.

Fabrics, Jacques, 1979, Spinel-olivine geothermometry in peridotites from ultramafic complexes: Contributions to Mineralogy 

and Petrology, v. 69, p. 329-336.

Findlay, D.C., 1969, Origin of theTulameen ultramafic-gabbro complex, southern British Columbia: Canadian Journal of Earth 

Sciences, v. 6, p. 399-425.
REFERENCES CITED 45

Floss, Christine, and Crozaz, Ghislaine, 1991, Ce anomalies in the 

LEW85300 eucrite: evidence for REE mobilization during 

Antarctic weathering: Earth and Planetary Science Letters, v. 

107, p. 13-24.

Ford, A.B., and Brew, D.A., 1988, Major-element geochemistry of 

metabasalts of the Juneau-Haines region, southeastern Alaska, 

in Galloway, J.P., and Hamilton, T.P, eds., Geological studies 

in Alaska by the U.S. Geological Survey during 1987: U.S. 

Geological Survey Circular 1016, p. 150-155.

Ford, A.B., and Brew, D.A., 1993, Geochemical character of upper 

Paleozoic and Triassic greenstone and related metavolcanic 

rocks of the Wrangellia terrane in northern southeastern Alaska, 

in Dusel-Bacon, Cynthia, and Till, A.B., eds., Geologic studies 

in Alaska by the U.S. Geological Survey, 1992: U.S. Geological Survey Bulletin 2068, p. 197-217.

Gehrels, G.E., McClelland, W.C., Samson, S.D., Patchett, P.J., and 

Jackson, J.L., 1990, Ancient continental margin assemblage in 

the northern Coast Mountains, southeast Alaska and northwest 

Canada: Geology, v. 18, p. 208-211.

Gehrels, G.E., and Saleeby, J.B., 1987, Geologic framework, tectonic evolution, and displacement history of the Alexander terrane: Tectonics, v. 6, p. 151-173.

Gehrels, G.E., Saleeby, J.B., and Berg, H.C., 1987, Geology of 

Annette, Gravina, and Duke Islands, southeastern Alaska: Canadian Journal of Earth Sciences, v. 24, p. 866-881.

Gray, Floyd, Page, N. J, Carlson, C.A., Wilson, S.A., and Carlson, 

R.R., 1986, Platinum-group element geochemistry of zoned 

ultramafic intrusive suites, Klamath Mountains, California and 

Oregon: Economic Geology, v. 81, p. 1252-1260.

Green, D.H., and Ringwood, A.E., 1967, The stability fields of aluminous pyroxene peridotite and garnet peridotite and their relevance in upper mantle structure: Earth and Planetary Science 

Letters, v. 3, p. 151-160.

Green, D.H., Ringwood, A.E., Ware, N.G., Hibberson, W.O., Major, A., and Kiss, E., 1971, Experimental petrology and petrogenesis of Apollo 12 basalts, in Levinson, A.A., ed., Proceedings of the Second Lunar Science Conference, Houston, Texas: 

Geochimica et Cosmochimica Acta, Supp. 2, v. 1, p. 601-615.

Guild, P.W, and Balsley, J.R., Jr., 1942, Chromite deposits of Red 

Bluff Bay and vicinity, Baranof Island, Alaska: U.S. Geological Survey Bulletin 936-G, p. 171-187.

Hammack, J.L., Nixon, G.T., Wong, R.H., and Paterson, W.P.E., 

1990, Geology and noble metal geochemistry of the Wrede 

Creek ultramafic complex, north-central British Columbia, in 

Geologic fieldwork 1989: British Columbia Ministry of Energy, Mines, and Petroleum Resources, Paper 1990-1, p. 405- 

415.

Hanson, G.N., 1980, Rare earth elements in petrogenetic studies of 

igneous systems: Annual Review of Earth and Planetary Sciences, v. 8, p. 371-406.

Harnois, Luc, and Morency, Maurice, 1989, Geochemistry of Mount 

Orford ophiolite complex, northern Appalachians, Canada: 

Chemical Geology, v. 77, p. 133-147.

Harnois, Luc, Trottier, Jacques, and Morency, Maurice, 1990, Rare 

earth element geochemistry of Thetford Mines ophiolite complex, northern Appalachians, Canada: Contributions to Mineralogy and Petrology, v. 105, p. 433-445.

Helz, R.T., 1973, Phase relations of basalts in the melting range at 

PH2O=5 kb as a function of oxygen fugacity: Journal of Petrology, v. 14, p. 249-302.

Henry, D.J., and Medaris, L.G., Jr., 1980, Application of pyroxene 

and olivine-spinel geothermometers to spinel peridotites in

southwestern Oregon: American Journal of Science, v. 280-A, 

p. 211-231.

Himmelberg, G.R., Brew, D.A., and Ford, A.B., 1986a, Chemical 

composition of olivine and orthopyroxene in peridotite of the 

Coast plutonic-metamorphic complex near Skagway, in 

Bartsch-Winkler, Susan, and Reed, K.M., eds., Geologic studies in Alaska by the U.S. Geological Survey during 1985: U.S. 

Geological Survey Circular 978, p. 95-98.

Himmelberg, G.R., and Loney, R.A., 1980, Petrology of ultramafic 

and gabbroic rocks of the Canyon Mountain ophiolite, Oregon: 

American Journal of Science, v. 280-A, p. 232-268.

Himmelberg, G.R., and Loney, R.A., 1981, Petrology of the ultramafic and gabbroic rocks of the Brady Glacier nickel-copper 

deposit, Fairweather Range, southeastern Alaska: U.S. Geological Survey Professional Paper 1195,26 p.

Himmelberg, G.R., Loney, R.A., and Craig, J.T., 1986b, Petrogenesis of the ultramafic complex at the Blashke Islands, southeastern Alaska: U.S. Geological Survey Bulletin 1662, 14 p.

Himmelberg, G.R., Loney, R.A., and Nabelek, PL, 1987, Petrogenesis of gabbronorite at Yakobi and northwest Chichagof 

Islands, Alaska: Geological Society of America Bulletin, 

v. 98, p. 265-279.

Holloway, J.R., and Burnham, C.W., 1972, Melting relations of basalt with equilibrium water pressure less than total pressure: 

Journal of Petrology, v. 13, p. 1-29.

Irvine, T.N., 1965, Chromian spinel as a petrogenetic indicator; part 

1, Theory: Canadian Journal of Earth Sciences, v. 2, p. 648- 

672.

Irvine, T.N., 1967a, The Duke Island ultramafic complexes, southeastern Alaska, Part 4.II in Wyllie, P.J., ed., Ultramafic and 

related rocks: New York, John Wiley, p. 84-97.

Irvine, T.N., 1967b, Chromian spinel as a petrogenetic indicator; 

part 2, Petrologic applications: Canadian Journal of Earth Sciences, v. 4, p. 71-103.

Irvine, T.N., 1973, Bridget Cove volcanics, Juneau area, Alaska: 

possible parental magma of Alaskan-type ultramafic complexes: 

Carnegie Institution Washington Yearbook, 72, 1972-1973, p. 

478^91.

Irvine, T.N., 1974, Petrology of the Duke Island ultramafic complex, southeastern Alaska: Geological Society of America Memoir 138, 240 p.

Irvine, T.N., 1976, Alaskan-type ultramafic-gabbroic bodies in the 

Aiken Lake, McConnel Creek, and Toodoggone map areas, in 

Report of activities, part A: Geological Survey Canada Paper 

76-1 A, p. 76-81.

Irvine, T.N., 1982, Terminology for layered intrusions: Journal of 

Petrology, v. 23,127-162.

Irvine, T.H. , and Smith, C.H., 1967, The ultramafic rocks of the 

Muskox intrusion, Northwest Territories, Canada, Part 2.III in 

Wyllie, P.J., ed., Ultramafic and related rocks: New York, John 

Wiley, p. 38^9.

Ishiwatari, Akira, 1985, Granulite-facies metacumulates of the 

Yakuno ophiolite, Japan: evidence for unusually thick oceanic 

crust: Journal of Petrology, v. 26, p. 1-30.

Ishizuka, Hideo, 1985, Prograde metamorphism of the Horokanai 

ophiolite in the Kamuikotan Zone, Hokkaido, Japan: Journal 

of Petrology, v. 26, p. 391-417.

IUGS Subcommission on the Systematics of Igneous Rocks, 1974, 

Classification and nomenclature of plutonic rocks, recommendations: Neues Jahrbuch fur Mineralogie Monatschefte, 1973, 

v. 4, p. 149-164.

Jackson, E.D., and Thayer, T.P., 1972, Some criteria for distinguish-
46 CHARACTERISTICS AND PETROGENESIS OF ALASKAN-TYPE ULTRAMAFIC-MAFIC INTRUSIONS, SE ALASKA

ing between stratiform, concentric, and alpine peridotite-gabbro complexes: International Geological Congress, 24th, 

Montreal, 1972, Proceedings, Section 2, p. 289-296.

James, O.B., 1971, Origin and emplacement of the ultramafic rocks 

of the Emigrant Gap area, California: Journal of Petrology, v. 

12, p. 523-560.

Jaques, A.L., and Green, D.H., 1980, Anhydrous melting of peridotite at 0-15 kb pressure and the genesis of tholeiitic basalts: 

Contributions to Mineralogy and Petrology, v. 73, p. 287-310.

Jenkins, D.M., 1983, Stability and composition relations of calcic 

amphiboles in ultramafic rocks: Contributions to Mineralogy 

and Petrology, v. 83, p. 375-384.

Karl, S.M., Brew, D.A., and Wardlaw, B.R., 1990, Significance of 

Triassic marble from Nakwasina Sound, southeastern Alaska, 

in Dover, J.H., and Galloway, J.P., eds., Geologic studies in 

Alaska by the U.S. Geological Survey, 1989: U.S. Geological 

Survey Bulletin 1946, p. 21-28.

Kay, S.M., and Kay, R.W., 1985a, Role of crystal cumulates and the 

oceanic crust in the formation of the lower crust of the Aleutian arc: Geology, v. 13, p. 461-464.

Kay, S.M., and Kay, R.W., 1985b, Aleutian tholeiitic and calc-alkaline magma series, I: the mafic phenocrysts: Contributions to 

Mineralogy and Petrology, v. 90, p. 276-290.

Kay, S.M., Kay, R.W., Brueckner, H.K., and Rubenstone, J.L., 1983, 

Tholeiitic Aleutian arc plutonism: the Finger Bay pluton, Adak, 

Alaska: Contributions to Mineralogy and Petrology, v. 82, p. 

99-116.

Kay, S.M., Kay, R.W., and Citron, G.P., 1982, Tectonic controls on 

tholeiitic and calc-alkaline magmatism in the Aleutian arc: Journal of Geophysical Research, v. 87-B, p. 4051^072.

Kay, S.M., Kay, R.W., Citron, G.P., and Perfit, M.R., 1990, Calcalkaline plutonism in the intra-oceanic Aleutian arc, Alaska, in 

Kay, S.M., and Rapela, C.W., eds., Plutonism from Antarctica 

to Alaska: Geological Society of America Special Paper 241, 

p. 233-255.

Kay, R.W., Rubenstone, J.L., and Kay, S.M., 1986, Aleutian terranes from Nd isotopes: Nature, v. 322, p. 605-609.

Kennedy, G.C., and Walton, M.S., Jr., 1947, Geology and associated mineral deposits of some ultrabasic rock bodies in southeastern Alaska: U.S. Geological Survey Bulletin 947-D, p. 65- 

84.

Komor, S.C., Elthon, Don, and Casey, J.F., 1985, Mineralogic variation in a layered ultramafic cumulate sequence at the North 

Arm Mountain massif, Bay of Islands ophiolite, Newfoundland: Journal of Geophysical Research, v. 90-B, p. 7705-7736.

Kretz, Ralph, 1983, Symbols for rock-forming minerals: The American Mineralogist, v. 68, p. 277-279.

Lanphere, M.A., 1968, Sr-Rb-K and Sr isotopic relationships in ultramafic rocks, southeastern Alaska: Earth and Planetary Science Letters, v. 4, p. 185-190.

Lanphere, M.A., and Eberlein, G.D., 1966, Potassium-argon ages 

of magnetite-bearing ultramafic complexes in southeastern 

Alaska [abs.]: Geological Society of America Special Paper 

87, p. 94.

Lathram, E.H., Pomeroy, J.S., Berg, H.C., and Loney, R.A., 1965, 

Reconnaissance geology of Admiralty Island, Alaska: U.S. 

Geological Survey Bulletin 1181-R, 48 p.

Leake, B.E., 1978, Nomenclature of amphiboles: Canadian Mineralogist, v. 16, p. 501-520.

LeBas, M.J., 1962, The role of aluminum in igneous clinopyroxenes 

with relation to their parentage: American Journal of Science, 

v. 260, p. 267-288.

Lindsley, D.H., and Andersen, D.J., 1983, A two-pyroxene thermometer; proceedings of the Thirteenth Lunar and Planetary Science Conference, part 2: Journal of Geophysical Research, v. 

88 Supp. A, p. A887-A906.

Loney, R.A., and Brew, D. A., 1987, Regional thermal metamorphism 

and deformation of the Sitka Graywacke, southern Baranof Island, southeastern Alaska: U.S. Geological Survey Bulletin 

1779, 17 p.

Loney, R.A., Brew, D.A., Muffler, L.J.P., and Pomeroy, J.S., 1975, 

Reconnaissance geology of Chichagof, Baranof, and Kruzof 

Islands, southeastern Alaska: U.S. Geological Survey Professional Paper 792, 105 p.

Loney, R.A., and Himmelberg, G.R., 1983, Structure and petrology 

of the La Perouse gabbro intrusion, Fairweather Range, southeastern Alaska: Journal of Petrology, v. 24, p. 377-423.

Loney, R.A., and Himmelberg, G.R., 1989, The Kanuti ophiolite, 

Alaska: Journal of Geophysical Research, v. 94-B, p. 15,869- 

15,900.

Loney, R.A., and Himmelberg, G.R., 1992, Petrogenesis of the Pdrich intrusion at Salt Chuck, Prince of Wales Island: an early 

Paleozoic Alaskan-type ultramafic body: Canadian Mineralogist , v. 30 p. 1005-1022.

Loney, R.A., Himmelberg, G.R., and Shew, Nora, 1987, Salt Chuck 

palladium-bearing ultramafic body, Prince of Wales Island, in 

Hamilton, T.D., and Galloway, J.P., eds., Geologic studies in 

Alaska by the U.S. Geological Survey during 1986: U.S. Geological Survey Circular 998, p. 126-127.

Loucks, R.R., 1990, Discrimination of ophiolitic from nonophiolitic 

ultramafic-mafic allochthons in erogenic belts by the Al/Ti ratio in clinopyroxene: Geology, v. 18, p. 346-349.

McDonough, W.F., and Frey, F.A., 1989, Rare earth elements in the 

upper mantle rocks, in Lipin, B.R., and McKay, G.A., eds., 

Geochemistry and mineralogy of rare earth elements: Reviews 

in Mineralogy, v. 21, p. 99-145.

Medaris, L.G., Jr., 1972, High-pressure peridotites in southwestern 

Oregon: Geological Society of America Bulletin, v. 83, p. 41- 

58.

Meen, J.K., Ross, O.K., and Elthon, Don., 1991, Gross isotopic heterogeneity in layered ultramafic cumulates [abs.]: EOS, Transactions of the American Geophysical Union, v. 72, p. 521.

Monger, J.W.H., Price, R.A., and Tempelman-Kluit, D.J., 1982, Tectonic accretion and the origin of the two major metamorphic 

and plutonic welts in the Canadian Cordillera: Geology, v. 10, 

p. 70-75.

Morimoto, N., Fabries, J., Ferguson, A.K., Ginzburg, I.V., Ross, M., 

Seifert, F.A., Zussman, J., Aoki, K., and Gottardi, G., 1988, 

Nomenclature of pyroxenes: American Mineralogist, v. 73, p. 

1123-1133.

Mortimer, N., 1986, Late Triassic, arc-related, potassic igneous rocks 

in the North American Cordillera: Geology, v. 14, p. 1035- 

1038.

Murray, C.G., 1972, Zoned ultramafic complexes of the Alaskan 

type: feeder pipes of andesitic volcanoes, in Shagam, R., and 

others, eds., Studies in earth and space sciences: Geological 

Society of America Memoir 132, p. 313-335.

Nicolas, A., 1992, Kinematics in magmatic rocks with special reference to gabbros: Journal of Petrology, v. 33, no. 4, p. 891-915.

Nixon, G.T., and Hammack, J.L., 1991, Metallogeny of ultramaficmafic rocks in British Columbia with emphasis on the platinum-group elements, in Ore deposits, tectonics and metallogeny in the Canadian Cordillera: British Columbia Ministry of Energy, Mines, and Petroleum Resources, Paper
REFERENCES CITED 47

1991-4, p. 125-161.

Nixon, G.T., Hammack, J.L., Connelly, J.N., Case, G., and Paterson, W.P.E., 1990, Geology and noble metal geochemistry of 

the Polaris ultramafic complex, north-central British Columbia, in Geological fieldwork 1989: British Columbia Ministry 

of Energy, Mines, and Petroleum Resources, Paper 1990-1, p. 

387-404.

Nixon, G.T., and Rublee, V.J., 1988, Alaskan-type ultramafic rocks 

in British Columbia: new concepts of the structure of the 

Tulameen complex, in Geologic fieldwork 1987: British Columbia Ministry of Energy, Mines, and Petroleum Resources, 

Paper 1988-1, p. 281-294.

Noble, J.A., andTaylor, H.P., Jr., 1960, Correlation of the ultramafic complexes of southeastern Alaska with those of other parts 

of North America and the world: International Geological Congress, 21st, Copenhagen, 1960, Report, part 13, p. 188-197.

Nye, C.J., and Reid, M.R., 1986, Geochemistry of primary and leastfractionated lavas from Okmok volcano, central Aleutians: 

implications for arc magmagenesis: Journal of Geophysical Research, v. 91-B, p. 10,271-10,287.

Pallister, J.S., and Hopson, C.A., 1981, Samail ophiolite plutonic 

suite: field relations, phase variation, cryptic variation and layering, and a model of a spreading ridge magma chamber: Journal of Geophysical Research, v. 86-B, p. 2593-2644.

Pallister, J.S., and Knight, R.J., 1981, Rare-earth element geochemistry of the Samail ophiolite near Ibra, Oman: Journal of Geophysical Research, v. 86-B, p. 2673-2697.

Perfit, M.R., Brueckner, Hannes, Lawrence, J.R., and Kay, R.W., 

1980, Trace element and isotopic variations in a zoned pluton 

and associated volcanic rocks, Unalaska Island, Alaska: a model 

for fractionation in Aleutian calcalkaline suite: Contributions 

to Mineralogy and Petrology, v. 73, p. 69-87.

Prinzhofer, Alain, and Allegre, C.J., 1985, Residual peridotites and 

the mechanisms of partial melting: Earth and Planetary Science Letters, v. 74, p. 251-265.

Robertson, E.G., 1956, Magnetite deposits near Klukwan and Haines, 

southeastern Alaska: U.S. Geological Survey Open-File Report, 37 p.

Roeder, PL., and Emslie, R.F., 1970, Olivine-liquid equilibrium: 

Contributions to Mineralogy and Petrology, v. 29, p. 275-289.

Rubin, C.M., and Saleeby, J.B., 1991, Tectonic framework of the 

upper Paleozoic and lower Mesozoic Alava sequence: a revised 

view of the polygenetic Taku terrane in southern southeast 

Alaska: Canadian Journal of Earth Sciences, v. 28, p. 881-893.

Rubin, C.M., and Saleeby, J.B., 1992, Tectonic history of the eastern edge of the Alexander terrane, southeast Alaska: Tectonics, 

v. 11, p. 586-602.

Ruckmick, J.C., and Noble, J.A., 1959, Origin of the ultramafic complex at Union Bay, southeastern Alaska: Geological Society of 

America Bulletin, v. 70, p. 981-1018.

Saleeby, J.B., 1991, Age and tectonic setting of the Duke Island 

ultramafic intrusion, southeast Alaska [abs.]: EOS, Transactions of the American Geophysical Union, v. 72, p. 521.

Samson, S.D., McClelland, W.C., Patchett, P.J., Gehrels, G.E., and 

Anderson, R.G., 1989, Evidence from neodymium isotopes for 

mantle contributions to Phanerozoic crustal genesis in the Canadian Cordillera: Nature, v. 337, p. 705-709.

Shaw, H.R., 1965, Comments on viscosity, crystal settling, and convection in granitic magmas: American Journal of Science, v. 

263, p. 120-152.

Simkin, Tom, 1967, Flow differentiation in the picritic sills of North

Skye, Part 3.Ill in Wyllie, P. J. ed., Ultramafic and related rocks: 

New York, John Wiley, p. 64-70.

Smith, C.H., 1962,. Notes on the Muskox intrusion, Coppermine 

River area, District of Mackenzie: Geological Survey of Canada 

Paper 61-25, 16 p.

Snoke, A.W., Quick, J.E., andBowman, H.R., 1981, Bear Mountain 

igneous complex, Klamath Mountains, California: an ultrabasic to silicic calc-alkaline suite: Journal of Petrology, v. 22, p. 

501-552.

Snoke, A.W., Sharp, W.D., Wright, J.E., and Saleeby, J.B., 1982, 

Significance of mid-Mesozoic peridotitic to dioritic intrusive 

complexes, Klamath Mountains-western Sierra Nevada, California: Geology, v. 10, p. 160-166.

Stebbins, R.H., 1957, Field description of the Percy Islands ultramafic complex, southeastern Alaska: New York, Columbia 

University, M.A. thesis.

Taylor, H.P., Jr., 1967, The zoned ultramafic complexes of southeastern Alaska, Part 4.III in Wyllie, P.J., ed., Ultramafic and 

related rocks: New York, John Wiley, p. 96-118.

Taylor, H.P., Jr., and Noble, J. A., 1960, Origin of the ultramafic complexes in southeastern Alaska: International Geological Congress, 21st, Copenhagen, 1960, Report, Part 13, p. 175-187.

Thorne, R.L., and Wells, R.R., 1956, Studies of the Snettisham magnetite deposit, southeastern Alaska: U.S. Bureau of Mines Report of Investigations 5195,41 p.

Turner, F.J., 1942, Preferred orientation of olivine crystals in peridotites, with special reference to New Zealand examples: Royal 

Society of New Zealand Transactions, v. 72, p. 280-300.

Ulmer, Peter, 1989, The dependence of the Fe2+-Mg cation-partitioning between olivine and basaltic liquid on pressure, temperature and composition, an experimental study to 30 kbars: 

Contributions to Mineralogy and Petrology, v. 101, p. 261-273.

Wager, L.R., Brown, G.M., and Wadsworth, W.J., 1960, Types of 

igneous cumulates: Journal of Petrology, v. 1, p. 73-85.

Walton, M.S., Jr., 1951, The Blashke Island ultrabasic complex, with 

notes on related areas in southeastern Alaska: U.S. Geological 

Survey Open-File Report [1586], 266 p.

Watkinson, D.H., and Melling, D.R., 1992, Hydrothermal origin of 

platinum-group mineralization in low-temperature copper sulfide-rich assemblages, Salt Chuck intrusion, Alaska: Economic 

Geology, v. 87, p. 175-184.

Wheatley, Michael, and Rock, N.M.S., 1988, SPIDER: a Macintosh 

program to generate normalized multi-element "spidergrams": 

American Mineralogist, v. 73, p. 919-921.

Wilson, A.H., 1992, The geology of the Great Dyke, Zimbabwe: 

crystallization, layering, and cumulate formation in the PI pyroxenite of Cyclic Unit 1 of the Darwendale Subchamber: Journal of Petrology, v. 33, p. 611-663.

Wones, D.R., 1979, The fractional resorption of complex minerals 

and the formation of strongly femic alkaline rocks, in Yoder, 

H.S. Jr., ed., The evolution of the igneous rocks; fiftieth anniversary perspectives: Princeton, N.J., Princeton University 

Press, p. 413-422.

Wyllie, P.J., ed., 1967, Ultramafic and related rocks: New York, John 

Wiley, 464 p.

Yokoyama, Kazumi, 1980, Nikubuchi peridotite body in the 

Sanbagawa metamorphic belt; thermal history of the 'Al-pyroxene-rich suite' peridotite body in high pressure metamorphic terrain: Contributions to Mineralogy and Petrology, v. 73, 

p. 1-13.

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