Petrographic and Chemical Data for the 

Large Mesozoic and Cenozoic Plutonic Sills 

East of Juneau, Southeastern Alaska 

U.S. GEOLOGICAL SURVEY BULLETIN 1918 
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Petrographic and Chemical Data for the 

Large Mesozoic and Cenozoic Plutonic Sills 

East of Juneau, Southeastern Alaska 

By JAMES L. DRINKWATER, DAVID A. BREW, and 

ARTHUR B. FORD 

U.S. GEOLOGICAL SURVEY BULLETIN 1918 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

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 

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Library of Congress Cataloging-in-Publication Data 

Drinkwater, J.L. 

Petrographic and chemical data for the large mesozoic and cenozoic 

plutonic sills east of Juneau, southeastern Alaska I by James L. Drinkwater, 

David A. Brew, and Arthur B. -Ford. 

p. cm.-(U.S. Geological Survey Bulletin; 1918.) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3:1918 

1. Sills (Geology)-Aiaska-Juneau Region. 2. Petrology-AlaskaJuneau Region. 3. Geology, Stratigraphic-Cretaceous. 4. Geology, 

Stratigraphic-Tertiary. I. Brew, David A. II. Ford, Arthur B. (Arthur Barnes), 

1932- . Ill. Title. IV. Series. 

QE75.B9 no. 1918 557.3 s-dc20 90-2838 

[QE611.5] [552' .3'097982] CIP 
CONTENTS 

Abstract 1 

Introduction 1 

Geologic setting 1 

Geochronology 3 

Methods 4 

Summary information 4 

Petrography 4 

Chemistry 5 

Comparisons 5 

Description of plutons 5 

Selected references 6 

FIGURES 

1. Index map showing location of the great tonalite sill 2 

2. Generalized geologic map of sills east of Juneau 3 

3. Diagrams showing average modal composition of sills east of Juneau ll 

4. Diagram showing mineral occurrences in sills east of Juneau 13 

5-8. Graphs showing: 

5. Color index distribution in sills east of Juneau 14 

6. An-content distribution in sills east of Juneau 15 

7. Normative An versus measured An content of samples from sills east of 

Juneau 16 

8. Si02 versus major oxides in sills east of Juneau 18 

9. AFM diagram of samples from sills east of Juneau 19 

10. Ternary diagram of normative Ab-An-Or content of rocks from sills east of 

Juneau 20 

11. Geologic map of the Mount Juneau pluton 22 

12. Plutonic rock diagram of Streckeisen (1973) for samples from the Mount 

Juneau pluton 23 

13. Geologic map of the Mendenhall Glacier pluton 26 

14. Plutonic rock diagram of Streckeisen (1973) for samples from the Mendenhall Glacier pluton 27 

15. Geologic map of the Lemon Creek Glacier pluton 30 

16. Plutonic rock diagram of Streckeisen (1973) for samples from the Lemon 

Creek Glacier pluton 31 

17. Geologic map of the Carlson Creek pluton 34 

18. Plutonic rock diagram of Streckeisen (1973) for samples from the Carlson 

Creek pluton 35 

19. Geologic map of the Annex Lakes pluton 38 

20. Plutonic rock diagram of Streckeisen (1973) for samples from the Annex 

Lakes pluton 39 

21. Geologic map of the Taku Cabin pluton 42 

22. Plutonic rock diagram of Streckeisen (1973) for samples from the Taku 

Cabin pluton 43 

23. Photographs of stained slabs from sills east of Juneau 46 

Contents Ill 
TABLES 

1. Summary of radiometric ages of plutonic sills, associated plutons, and metamorphic country rock east of Juneau 10 

2. Petrographic characteristics of plutonic sills east of Juneau 12 

3. Average major-element chemistry for plutonic sills east of Juneau 17 

4. Chemical characteristics of plutonic sills east of Juneau 17 

5. Organization of figures and tables with data on individual plutons 21 

6. Petrographic and major-element chemical data for the Mount Juneau 

pluton 23 

7. Petrographic and major-element chemical data for the Mendenhall Glacier 

pluton 27 

8. Petrographic and major-element chemical data for the Lemon Creek Glacier 

pluton 31 

9. Petrographic and major-element chemical data for the Carlson Creek 

pluton 35 

10. Petrographic and major-element chemical data for the Annex Lakes 

pluton 39 

11. Petrographic and major-element chemical data for the Taku Cabin 

pluton 43 

IV Contents 
Petrographic and Chemical Data for the 

Large Mesozoic and Cenozoic Plutonic Sills 

East of Juneau, Southeastern Alaska 

By James L. Drinkwater, David A. Brew, and Arthur B. Ford 

Abstract 

Petrographic, chemical, and age data are presented for 

six plutonic sills of Late Cretaceous to early Tertiary age 

located east of Juneau, Alaska. Five of the sills-the Mount 

Juneau, Carlson Creek, Lemon Creek Glacier, Mendenhall 

Glacier, and Taku Cabin plutons-are mostly tonalite but 

range from quartz diorite to granodiorite; their mean color 

indexes range from 19 to 32. The more silicic Annex Lakes 

pluton is mostly granodiorite but has significant quartz monzodiorite and tonalite and a mean color index of 14. Although 

the six plutons are calc-alkaline and generally similar in 

average chemical and modal composition, they vary in form, 

mineralogy, texture, and petrographic and chemical characteristics. The Mount Juneau and Annex Lakes plutons exhibit 

the greatest internal differences, whereas the Taku Cabin and 

Mendenhall Glacier plutons are the most homogeneous. 

Plots on silica-oxide variation and AFM diagrams exhibit 

coherent trends with some scatter. 

INTRODUCTION 

This report contains preliminary petrographic and 

chemical data for a group of six plutonic sills of Late 

Cretaceous to early Tertiary age located east of Juneau, 

Alaska (fig.1). The plutons are part of what Brew (1988) 

termed the "great tonalite sill," which was previously 

called the Coast Plutonic Complex sill belt by Brew and 

Morrell (1983). This sill belt is part of a larger unit 

informally called the Coast plutonic-metamorphic complex (Brew and Ford, 1984a, b). The great tonalite sill is 

a composite linear batholith that extends for more than 

900 kilometers along the length of southeastern Alaska 

from north of Skagway south into British Columbia (fig. 

1 ). The investigation of the six plutons is important in 

understanding the emplacement history and petrogenesis 

of the large composite tonalitic sill belt. The location of 

Manuscript approved for publication, November 21, 1989. 

the variably deformed and metamorphosed sill bodies in 

the zone of most intense metamorphism and deformation 

of a major tectonic welt (Brew and Ford, 1978, 1981, 

1985; Monger and others, 1982) makes them a critical 

element in studying the timing of plutonism, deformation, and regional metamorphism of the region. 

Locations of the plutons-herein called the Juneau 

sills- are shown in figures 1 and 2, and the regional 

geologic setting is summarized in figure 2. The locations 

of samples used in modal and chemical analysis are 

shown on geologic sketch maps of each pluton in the 

section "Description of Plutons." The Mendenhall Glacier pluton extends much farther northward than the 

study area, but only the southernmost segment of the 

pluton is included in this study. 

Information presented here includes descriptive 

summaries, modal analyses, rock-classification diagrams, 

petrographic data, and major-element chemistry for each 

pluton. Pluton summary information is presented as plots 

of average modal and average chemical analyses, tables 

of petrographic characteristics and mineral occurrences, 

and frequency distribution charts of color index and 

estimated anorthite (An) content of plagioclase. Binary 

and ternary variation diagrams are included to show the 

petrologic affinity and classification of the rocks. 

This report provides information for comparative 

studies of segments of the great tonalite sill and supports 

future investigations, synthesis, and related work. 

GEOLOGIC SETTING 

The Juneau sills form a discontinuous segment of 

the great tonalite sill (Brew, 1988), a long and narrow 

belt of sheet-like orthogneiss plutons (Brew and Ford, 

1981) of Late Cretaceous to early Tertiary age (fig. 1). 

The 3- to 25-km-wide belt consists of numerous individual sills of tonalite with minor granodorite and quartz 

diorite. The sills typically are strongly foliated to gneissic 

in texture and display other moderate to strong metaGeologic Setting 
morphic characteristics. The sills dip steeply east. They 

separate metamorphic rocks with Paleozoic and Meso0 

EXPlANATION 

• Great tonalite sill 

LZ:2J Central part of the 

Coast plutonicmetamorphic 

complex-Unfoliated granitic 

rocks, and some 

schist, gneiss, 

and migmatite 

-?-Contact-Dashed 

where approximate; queried 

where uncertain 

Figure 1. Index map showing location of the great tonalite sill 

(Brew, 1988) and central granitic part of the (informal) Coast 

plutonic-metamorphic complex (Brew and Ford, 1984a, b). 

Eastern contact of the latter in Canada not shown. 

zoic protolith ages on the west from Tertiary granitic 

rocks and gneisses with Paleozoic protolith ages on the 

east. The rocks on the east constitute the central part of 

the (informal) Coast plutonic-metamorphic complex of 

Brew and Ford (1984a, b). These two separated units 

were called the western metamorphic and central granitic 

zones by Brew and Ford (1981 ), and they roughly coincide with parts of the Taku and Tracy Arm tectonostratigraphic terranes of Berg and others (1978). The 

significance of this was discussed by Brew and Ford 

(1978, 1981, 1984b), who believe that the sills were 

emplaced near a major structural boundary but reject the 

concept that the Taku and Tracy Arm terranes were 

separately accreted and are disparate tectonostratigraphic terranes. The relations between ages of intrusion, 

metamorphism, and deformation are discussed in Brew 

and Ford (1981), Brew and others (1989a, b) and Gehrels and others (1984). 

The six sills east of Juneau range from 1 to 8 km in 

width and are separated from each other by screens of 

migmatitic gneiss and amphibolite-grade schist (fig. 2). 

Each pluton trends northwest and dips easterly in concordance with the regional structure; the Mount Juneau 

pluton, however, truncates the regional structure at its 

northern end. The regional geology of the area is summarized in Brew and Ford (1986), and detailed maps by 

Ford and Brew (1973) and Brew and Ford (1977) cover 

most of the area. Earlier geologic descriptions and maps 

of parts of the area are found in Twenhofel (1952), 

Sainsbury (1953), and Plafker (1962). 

The Juneau sills are composed mostly of tonalite 

and contain lesser but significant amounts of granodiorite and quartz diorite. Hornblende is the predominant 

mafic mineral except in the Mount Juneau and Annex 

Lakes plutons, where biotite is more abundant. All the 

sills are strongly foliated, but the well-developed gneissic 

layering displayed by the Mount Juneau, Lemon Creek 

Glacier, and Carlson Creek plutons is absent in the Taku 

Cabin and Mendenhall Glacier plutons. The Annex 

Lakes pluton, which is mostly biotite granodiorite, is only 

moderately to weakly foliated but locally displays a weak 

gneissic layering and strong foliation. The foliation and 

gneissic layering generally parallel the margins of the sills 

and the foliation in the country rock. 

The Annex Lakes pluton is larger and more leucocratic than the other plutons and is the most varied 

lithologically and texturally; it may be a composite body 

that is intermediate in character between the sills to the 

west and the massive homogeneous granodiorite of the 

Turner Lake pluton to the east. Whether the more 

massive homogeneous core of the Annex Lakes pluton, 

which has been separately called the Flat Point pluton by 

Brew and Ford (1977), is a differentiated phase of the 

Annex Lakes pluton or a separate pluton is uncertain; it 

is treated in this report as part of the Annex Lakes 

pluton. 

2 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
GEOCHRONOLOGY 

A summary of radiometric ages for the plutonic 

sills and associated rocks east of Juneau is shown in table 

1. All the K-Ar ages except that of the Turner Lake 

pluton are interpreted as minimum ages. The three most 

deformed and metamorphosed sills (Mount Juneau, 

Carlson Creek, and Lemon Creek Glacier plutons) are 

older than the foliated but less deformed Taku Cabin and 

Mendenhall Glacier plutons, and they were apparently 

emplaced into an environment of more active deformaij ~ ~ ~ ~ ~ ~ \ 

-~ 4' "' ij ~ -'l "· II\ co = \ a • ~ • ~ • ~ • 

Mendenhall Glacier 

pluton 

TKs 

Lemon Creek Glacier 

pluton 

D Foliated tonalite 

D Heterogeneous foliated 

granodiorite 

TKg 

Massive homogeneous granodiorite 

and minor granite 

Annex 

pluton 

\~::c :r~"'"-­ "'- x' '-.._) 

Migmatitic gneiss and schist, undivided 

(Tertiary to Cretaceous) 

~ Schist, undivided (Tertiary to Cretaceous)-

Greenschist and amphibolite-grade schist 

Contact-Dashed where approximate 

Fault-Dashed where approximate 

tion and metamorphism. The K-Ar hornblende age of 

66.5 Ma from the Mount Juneau pluton (table 1) closely 

agrees with the U-Pb age of 67 ± 2 Ma on zircons from 

the Carlson Creek pluton reported by Gehrels and others 

(1984), but it is a minimum age. Preliminary results of 

current studies (D.A. Brew and A.B. Ford, unpub. data, 

1989) suggest that the Mount Juneau pluton is older than 

the Carlson Creek pluton. The undeformed core (Flat 

Point pluton) of the variably deformed and synkinematically emplaced Annex Lakes pluton yielded a U-Pb age 

of 60.0 Ma that registers the end of intense deformation 

0 2 4 6 8 10 KILOMETERS 

Figure 2. Geologic sketch map showing large sills in the (informal) Coast plutonic-metamorphic complex of Brew and Ford 

(1984b) east of Juneau. Plutons in bold type are those discussed in text. 

Geochronology 3 
and metamorphism (Gehrels and others, 1984). The 

Mendenhall Glacier and Taku Cabin plutons are latesynkinematically emplaced bodies (Brew and others, 

1989a) with inferred ages between 55 and 60 Ma. K-Ar 

ages of 51 to 56 Ma on biotite-hornblende pairs from the 

migmatitic gneiss country rock reported by Forbes and 

Engels (1970) agree well with unpublished ages from 

J.G. Smith (1974) of 52 to 57 Ma on similar gneissic 

country rocks. The K-Ar ages of the sills and gneissic 

country rock probably reflect the latest major thermal 

event related to emplacement of the Turner Lake pluton 

(fig. 2). 

METHODS 

The information in this report is based largely on 

field notes, chemical analyses, and examination of stained 

rock slabs and thin sections. Rock names given in this 

report are based on modes (fig. 3) plotted on the rock 

classification diagram of Streckeisen (1973). Modes (percent quartz, K-feldspar, plagioclase, and mafic minerals) 

were determined by counting roughly 1,000 points on 

rock slabs stained for K-feldspar and plagioclase by the 

method of Norman (1974), and results are shown in 

tables and on triangular plots of K-feldspar, quartz, and 

plagioclase recalculated to 100 percent. Biotite and hornblende were counted together as total mafic minerals. 

The data for the Mount Juneau pluton include separate 

percentages for biotite, hornblende, epidote, chlorite, 

and total accessories, based on thin sections point counted in a previous study (Ford and Brew, 1981). In studies 

of the other plutons, relative amounts of biotite and 

hornblende were visually estimated by thin-section examination. 

Major-element chemical analyses were done by 

whole-rock X-ray fluorescence determinations or by rapid rock methods (pre-1970 samples) at U.S. Geological 

Survey laboratories in Menlo Park, Calif., and Denver, 

Colo. The data were converted to normalized oxides and 

CIPW norms by the PETCAL 4 computer program 

(Bingler and others, 1976), and results were tabulated on 

a volatile-free basis for each pluton; an average chemical 

composition for each pluton was also tabulated. Normative An content of plagioclase and color index (CI) are 

also reported. 

SUMMARY INFORMATION 

Summary information is presented in both tables 

and figures that summarize the results of petrographic 

and chemical analyses for all plutons. In addition, variation and discriminant diagrams present data from each 

pluton for comparative studies. The Mendenhall Glacier 

body may have different petrographic and chemical characteristics outside of the study area. 

Petrography 

The general petrographic characteristics of the sills 

are listed in table 2, average modal compositions are 

plotted in figure 3, the occurrence of minerals is summarized in figure 4, and distribution of color index is shown 

in figure 5. Tonalite is the predominant composition, 

although much of the margins of the plutons is either 

quartz diorite or quartz monzodiorite. Plagioclase, 

quartz, hornblende, and biotite are the most common 

minerals in the sills; K-feldspar and iron oxides occur in 

trace to minor amounts in most of the rocks. Garnet is 

common in the Mount Juneau pluton, less common in 

the Carlson Creek and Lemon Creek Glacier plutons, 

and rare or absent in the other plutons. Coarse, wellformed, subhedral, zoned epidote is also common in the 

Mount Juneau pluton; epidote is rare in the other 

plutons and generally is found only in border-phase 

rocks. Traces of pyroxene were found only in the Carlson 

Creek and Mendenhall Glacier plutons; the pyroxene 

occurs as relict cores in hornblende or in cummingtonitehornblende aggregates. Sphene is a common accessory 

mineral in all but the Carlson Creek and Lemon Creek 

Glacier plutons. In general, euhedral sphene occurs as 

large discrete well-formed grains, whereas anhedral 

sphene occurs as interstitial grains or granular intergrowths with mafic minerals. Subhedral sphene occurs 

either as discrete, rounded, or abraded grains or as 

well-developed intergrowths with mafic minerals. Clots 

of granular magnetite and anhedral apatite are common 

in the Taku Cabin and Mendenhall Glacier plutons. The 

nature of the clots is unclear; generally they are clustered 

with mafic minerals and may be a product of late 

crystallization or of hydrothermal derivation rather than 

a product of early crystallization or of xenolithic origin. 

The clots locally include subhedral zircon. 

Chlorite, which is mostly found intergrown with 

biotite in rocks of the tonalite sills, typically exhibits 

characteristic anomalous interference colors under 

crossed nicols (table 2). Chlorite with anomalous blue 

colors is predominant in the Mount Juneau and Lemon 

Creek Glacier plutons, whereas chlorite with anomalous 

brown colors distinguishes the Mendenhall Glacier and 

Taku Cabin plutons. Chlorite with brown or blue interference colors is typical of the Carlson Creek and Annex 

Lakes plutons, but rarely are both chlorite types found in 

the same thin section. The anomalous interference colors 

are indicators of the composition and oxidation state of 

chlorite (Deer and others, 1975); brown colors indicate a 

more oxidized chlorite with higher percentage of trivalent 

iron (Fe20 3 ). 

The An percent of plagioclase was estimated optically by the Michel-Levy method on appropriate plagioclase grains using the diagram from Jones and Bloss 

(1980). Optically measured An compositions were used 

instead of normative An compositions in constructing 

4 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
figure 6 since more An data are available from optical 

measurements than from chemical analyses. The pattern 

of An distribution based on optically measured An 

content does not vary much from that based on normative values since a linear relationship exists between the 

results of the two methods (fig. 7) with significant scatter 

for both high and low values. The normative values 

consistently average 7 to 10 percent higher than values 

measured optically. 

Chemistry 

Major-element chemical data are summarized in 

tables 3 and 4, and data for individual plutons are 

presented in the "Description of Plutons" section. Binary 

and ternary variation diagrams (figs. 8-10) are presented 

to show chemical characteristics of the plutons; they do 

not necessarily imply common genetic relations or linkages of a differentiation sequence. 

Major-element oxides plotted on variation diagrams (fig. 8) show fairly coherent but slightly scattered 

distribution patterns. The linear trends of decreasing 

MgO, FeO* (total iron), and Ti02 with increasing Si02 

are the most distinctive variations for the sills as a group. 

The sill rocks are largely metaluminous as indicated by 

their Al20 3/(Ca0+ Na20+ K2 ) ratios (A/CNK ratios) of 

less than 1 (table 4), according to the classification of 

Shand (1949). The Annex Lakes pluton has higher 

A/CNK values, closer to 1 but less than 1.1 (table 4). The 

calc-alkaline character of the sill rocks is evident by their 

diopside and quartz normative compositions (tables 

6B-11B), AFM plots (fig. 9), and except for the Annex 

Lakes pluton, average alkali-lime indexes of < 1 (table 

4). Sill rocks plot mostly as tonalite in Barker's (1979) 

ternary diagram of normative feldspar composition (fig. 

10). 

Comparison of norms with modes shows some 

discrepancies. Orthoclase, in particular, is generally 

much higher in the norm than in the mode (compare figs. 

3, 10; see also tables 6-11). This discrepancy is probably 

due to the incorporation of K into early formed mafic 

minerals-biotite and hornblende-that arc not calculated in the CIPW norms. Biotite is common in Juneau sill 

rocks, and the K it contributes to chemical analyses is 

attributed to orthoclase during calculation of CIPW 

norms, thus leading to erroneously high orthoclase values. Similarly, normative magnetite is high in samples 

from the Mount Juneau, Lemon Creek Glacier, and 

Carlson Creek plutons (tables 6, 8, 9), although visual 

examination of thin sections reveals very little opaque 

oxides (magnetite or ilmenite) in those samples. Biotite 

incorporates much trivalent iron (Fe +3 ) (Deer and others, 1975), which is used to make magnetite in calculations of normative compositions. 

The differentiation index (DI), which is calculated 

from the norms, can provide clues to the stage of 

fractionation of a rock. The average DI of the plutonic 

sills (table 4) ranges from a low of 42 (Lemon Creek 

Glacier pluton) to a high of 68 (Annex Lakes pluton); the 

other four tonalitic sills exhibit a much shorter range in 

average DI (53 to 56). 

Comparisons 

Comparisons of the data indicate close similarities 

between the plutonic sills in their average modal and 

chemical compositions (fig. 3; table 3), with the Annex 

Lakes pluton being least like the other sills. Differences 

between the plutonic sills are indicated by their petrographic and chemical characteristics (tables 2, 4), clustering patterns on the AFM diagram (fig. 9), and 

distribution of color index and An content (figs. 5, 6). 

The Lemon Creek Glacier pluton is the most mafic 

of the sills as indicated by its higher content of mafic 

minerals, lower Si02 abundances, and lowest average 

values of differentiation index (DI), alkali-lime index, 

and A/CNK ratio. 

The Annex Lakes pluton is the most varied and 

heterogeneous of the sills in its chemistry, lithology, and 

petrographic characteristics. It is the most siliceous and 

least mafic rich of the sills and contains more but variable 

amounts of K-feldspar. It also shows the highest average 

DI and alkali-lime index, and higher A/CNK values than 

the other sills. Five samples from the Annex Lakes pluton 

are slightly corundum normative (table lOB) and thus 

exemplify the diverse nature of this pluton. 

Of the five tonalite sills, the Mount Juneau pluton 

exhibits the greatest range in modal mineral abundances, 

Si02 , total iron, CaO, total alkali oxides, and scatter on 

the AFM diagram, as well as the most varied mineralogy. 

Abundant garnet and subhedral epidote are typical of the 

Mount Juneau pluton, and sphene and allanite occur 

there in much more abundance than in the other tonalite 

sills. Data for the Mount Juneau pluton show a gap in 

silica content from 56 to 60 percent (table 6B), whereas 

all but one of the samples from the Lemon Creek Glacier 

pluton fall within 56 to 60 percent Si02 (table 8B); this 

pattern may suggest a genetic link between the two 

plutons. The Taku Cabin and Mendenhall Glacier plutons are similar in their petrographic characteristics 

(table 2), chemistry (tables 3, 4), average modal composition (fig. 3), and megascopic description (tables 7, 11 ); 

they are the most homogeneous, and least deformed and 

metamorphosed of the tonalite sills. 

DESCRIPTION OF PLUTONS 

Data for each pluton are arranged as shown in 

table 5 and are presented in figures 12-22 and tables 

6-11. These data include (1) a geologic sketch map with 

Description of Plutons 5 
sample localities, (2) a QAP (quartz-alkali feldsparplagioclase) diagram, and (3) a table consisting of descriptive information, petrographic data, and majorelement chemical data. Additional petrographic features 

of the sills are presented in' table 2. Symbols and abbreviations used in the tables are explained either in headnotes to tables or in table 5. Photographs of typical 

representative rock samples of each pluton are shown in 

figure 23. Sample localities, shown by numbered dots on 

geologic maps of plutons, represent samples that were 

point counted or chemically analyzed or both. The map 

numbers are listed in tables of petrographic data (tables 

6A-11A) and (or) tables of chemistry (tables 6B-11B). 

All modes plotted on the Streckeisen (QAP) diagram are based on point counts of stained slabs. For 

samples with no stained slabs and therefore no modal 

analysis, the modes and rock classification were estimated visually from thin sections and the rock names are 

reported in the far left column of tables of petrographic 

data (tables 7A-11A). For these samples, mafic mineral 

abundance (color index) was estimated by use of standard charts for estimating percentage composition of 

rocks; it is reported in the "Mafic minerals" column of 

the tables of petrographic data. The abundances of 

hornblende, biotite, opaque minerals, and sphene were 

visually estimated by thin section examination. For the 

Mount Juneau pluton, individual percentages of mafic 

minerals previously point counted from thin sections 

(Ford and Brew, 1981) were available for this study. 

Hornblende includes all primary and secondary brown 

and green amphiboles. The An percent was estimated by 

the Michel-Levy method on appropriate plagioclase 

grains, and the diagram from Jones and Bloss (1980) was 

used to determine the plagioclase composition. 

Data for the Lemon Creek Glacier pluton are 

divided into main- and border-phase rocks; averages of 

modal analyses are for main-phase rocks only. The 

border-phase rocks consist of more highly deformed and 

metamorphosed orthogneiss than the main-phase rocks. 

The data for the Flat Point pluton are distinguished from 

the data for the Annex Lakes pluton and are not used in 

the Annex Lakes averages. 

SELECTED REFERENCES 

Barker, Fred, 1979, Trondhjemite-Definition, environment 

and J1ypotheses of origin, in Barker, Fred, ed., Trondhjemites, dacites, and related rocks: New York, Elsevier, 

p.l-12. 

Berg, H.C., Jones, D.L., and Coney, P.J.) 1978, Map showing 

pre-Cenozoic tectonostratigraphic terranes of southeastern Alaska and adjacent areas: U.S. Geological Survey 

Open-File Report 78-105, scale 1:1,000,000. 

Dingler, E.C., Trexler, D.T., Kemp, W.R., and Bonham, H.P., 

Jr., 1976, PETCAL-A Basic language computer program for petrologic calculations: Nevada Bureau of 

Mines and Geology Report 28, 27 p. 

Brew, D.A., 1988, Latest Mesozoic and Cenozoic igneous rocks 

of southeastern Alaska-A synopsis: U.S Geological 

Survey Open-file Report 88-405,.29 p. 

Brew, D.A., and Ford, A.B., 1977, Preliminary geologic and 

metamorphic-isograd map of the Juneau B-1 quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-846, scale 1:31,680. 

---1978, Megalineament in southeastern Alaska marks 

southwest edge of Coast Range batholithic complex: 

Canadian Journal of Earth Science, v. 15, no. 11, p. 

1763-1772. 

---1981, The Coast plutonic complex sill, southeastern 

Alaska, in Albert, N.R.D., and Hudson, Travis, eds., The 

U.S. Geological Survey in Alaska-Accomplishments 

during 1979: U.S. Geological Survey Circular 823-B, p. 

B96-B99. 

---1984a, The northern Coast plutonic complex, southeastern Alaska and northwestern British Columbia, in Coonrad, W.L., and Elliott, R.L., eds., The U.S. Geological 

Survey in Alaska-Accomplishments during 1981: U.S. 

Geological Survey Circular 868, p. 120-124. 

---1984b, Tectonostratigraphic terranes in the Coast 

plutonic-metamorphic complex, southeastern Alaska, in 

Bartsch-Winkler, Susan, and Reed, K.M., eds., The United States Geological Survey in Alaska-Accomplishments during 1982: U.S. Geological Survey Circular 939, 

p. 90-93. 

---1984c, Timing of metamorphism and deformation of the 

Coast plutonic metamorphic complex near Juneau, Alaska [ abs.]: Geological Society of America Abstracts with 

Programs, v. 16, no. 5, p. 272. 

---1985, The 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. 

---1986, Preliminary reconnaissance geologic map of the 

Juneau, Taku River, Atlin, and part of the Skagway 

1:250,000 quadrangles, southeastern Alaska: U.S. Geological Survey Open-File Report 85-395, 23 p. 

Brew, D.A., Ford, A.B., Grybeck, Donald, Johnson, B.R., and 

Nutt, C.J., 1976, Key foliated quartz diorite sill along 

southwest side of Coast Range complex, northern southeastern Alaska, in Cobb, E.H., ed., The United States 

Geological Survey in Alaska-Accomplishments during 

1975: U.S. Geological Survey Circular 733, p. 60. 

Brew, D.A., Ford, A.B., and Himmelberg, G.R., 1989a, Evolution of the western part of the Coast plutonicmetamorphic complex, southeastern Alaska, USA-A 

summary, in Daly, J.S., and others, eds., Evolution of 

metamorphic belts: Geological Society of America Special Publication 42, p. 447-452. 

---1989b, Relative timing of pluton emplacement and 

regional deformation, northern southeastern Alaska 

[abs.]: Geological Society of America Abstracts with 

Programs, v. 21, no. 5, p. 59. 

Brew, D.A., and Morrell, R.P., 1980, Preliminary map of 

intrusive rocks in southeastern Alaska: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-1048, scale 

1:1,000,000. 

---1983, Intrusive rocks and plutonic belts in southeastern 

Alaska, in Roddick, J.A., ed., Circum-Pacific plutonic 

6 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
terranes: Geological Society of America Memoir 159, p. 

171-193. 

Deer, W.A., Howie, R.A., and Zussman, J., 1975, An introduction to the rock-forming minerals: London, Longman, 

528 p. 

Forbes, R.B., and Engels, J.C., 1970, 40Kf0 Ar age relations of 

the Coast Range batholith and related rocks of the 

Juneau ice field area, Alaska: Geological Society of 

America Bulletin, v. 81, p. 579-584. 

Ford, A.B., and Brew, D.A., 1973, Preliminary geologic and 

metamorphic-isograd map of the Juneau B-2 quadrangle, Alaska: U.S. Geological Survey Miscellanous Field 

Studies Map MF-527, scale 1:31,680. 

---1981, Orthogneiss of Mount Juneau-An early phase of 

coast mountain plutonism involved in Barrovian regional 

metamorphism near Juneau, in Albert, N.R.D., and 

Hudson, Travis, eds., The United States Geological 

Survey in Alaska-Accomplishments during 1979: U.S. 

Geological Survey Circular 823-B, p. B99-B101. 

Gehrels, G.B., Brew, D.A., and Saleeby, J.B., 1984, Progress 

report on U/Pb (zircon) geochronologic studies in the 

Coast plutonic-metamorphic complex east of Juneau, 

southeastern Alaska, in Reed, K.M., and BartschWinkler, Susan, eds., The United States Geological 

Survey in Alaska-Accomplishments during 1982: U.S. 

Geological Survey Circular 939, p. 100-102. 

Irvine, T.N., and Baragar, W.R., 1971, A guide to the chemical 

classification of the common volcanic rocks: Canadian 

Journal of Earth Sciences, v. 8, no. 5, p. 523-548. 

Jones, N.W., and Bloss, F.D., 1980, Laboratory manual for 

optical mineralogy: Minneapolis, Minn., Burgess Publishing Co., p. 17-4. 

Monger, J.W.H., Price, F.A., and Tempelman-Kluit, D.J., 1982, 

Tectonic accretion and the origin of two major metamorphic and plutonic welts in the Canadian Cordillera: 

Geology, v. 10, p. 70-75. 

Norman, M.B., 1974, Improved techniques for selective staining of feldspar and other minerals using amaranth: U.S. 

Geological Survey Journal of Research, v. 2, no. 1, p. 

73-79. 

Platker, George, 1962, Geologic investigations of proposed 

power sites at Sheep Creek, Carlson Creek, and Turner 

Lake, Alaska: U.S. Geological Survey Bulletin 1031-F, 

p. F127-F148. 

Sainsbury, C:L., 1953, Geology of the Olds Mountain-Clark 

Peak area, Juneau vicinity, Alaska: U.S. Geological 

Survey Open-File Report 53-231, 43 p. 

Shand, S.J., 1949, Emptive rocks: New York, John Wiley and 

Sons Inc., 488 p. 

Streckeisen, A.L., 1973, Plutonic rocks-Classification and 

nomenclature recommended by lUGS Subcommission 

on Systematics of Igneous Rocks: Geotimes, v. 18, p. 

26--30. 

Twenhofel, W.S., 1952, Geology of the Alaska-Juneau lode 

system, Alaska: U.S. Geological Survey Open-File Report 52-160, 170 p. 

Zen, E-an, and Hammarstrom, J.M., 1984, Magmatic epidote 

and its petrologic significance: Geology, v. 12, p. 

515-518. 

Selected References 7 

FIGURES 3-23; TABLES 1-11 
Table 1. Summary of radiometric ages of plutonic sills, associated plutons, and metamorphic 

country rock east of Juneau 

Body Mineral Dating Age Reference 

(Sample No 0) method (Ma) 

Mount Juneau Biotite K-Ar 54o0±2 Brew and Smith 

pluton Hornblende K-Ar 66o5±2 (unpubo data,1974) 

(64ABD43B) 

Mendenhall Biotite K-Ar 53o8±2 Brew and Smith 

Glacier pluton Hornblende K-Ar 55o0±2 (unpubo data,1974) 

(65ABD284) 

Mount Juneau Hornblende K-Ar 57. 5±2 Wilson and Brew 

pluton (unpubo data,1984) 

(76AF030A) 

Lemon Creek(?) Biotite K-Ar 53 0 8±1 0 6 Forbes and 

pluton Hornblende K-Ar 56o1 ±1 o2 Engels ( 1 970) 

(TVC-1-1) 

Carlson Creek Zircon U-Pb 67o0±2 Gehrels and 

pluton others (1984) 

(81GS5) 

Flat Point -Zircon U-Pb 60o0±4 Gehrels and 

pluton others (1984) 

(82GS112) 

Migmati te of Biotite K-Ar 53o8±2 Brew and Smith 

Observation Peak Hornblende K-Ar 57o4±2 (unpubo data,1974) 

(65ABD312) 

Homogeneous Biotite K-Ar 52o0±2 Brew and Smith 

gneiss Hornblende K-Ar 55o4±2 (unpubo data,1974) 

(65ABD50A) 

Turner Lake Zircon U-Pb 50o0±2 Gehrels and 

pluton others (1984) 

(82GS111) 

10 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
QUARTZ(Q) 

ALKALI-FELDSPAR (A) PLAGIOCLASE FELDSPAR (P) 

EXPLANATION 

/-"T"""-----~--~-\. Quartz X AL • MJ 

& TC \l CC 

MG EB LC 

Alkali feldspar Plagioclase feldspar 

Figure 3. Average modal composition of large sills east of Juneau. Classification 

diagram is from Streckeisen (1973). AL, Annex Lakes pluton; TC, Taku Cabin pluton; 

MG, Mendenhall Glacier pluton; MJ, Mount Juneau pluton; CC, Carlson Creek pluton; 

LC, Lemon Creek Glacier pluton. 

Figures 3-23; Tables 1-11 11 
Table 2. Petrographic characteristics of plutonic sills east of Juneau 

Pluton- - - - -

Plagioclase (pet) 

Average (pet) 

Quartz (pet) 

Average (pet) 

K-feldspar (pet) 

Average (pet) 

Mount 

Juneau 

47-65 

55.2 

6-25 

17.8 

0-17 

4.9 

Mafic minerals (pet) 10-37 

Average (pet) 22.5 

Major mafic 

mineral 

Biotite 

Major rock type Tonalite 

Minor rock type Granodiorite, 

quartz diorite 

Major acces- Garnet, epidote 

sory sphene 

An range (pet) 

Average An (pet) 

32-40 

37 

Carlson 

Creek 

50-66 

56.6 

8-28 

18.9 

0-14 

2.7 

10-36 

23.8 

Hornblende 

Tonalite 

Quartz diorite 

Apatite 

33-45 

38 

Main 

texture/fabric 

Foliated, Foliated, 

Distinguishing 

features 

Chlorite 

Hornblende 

color/form 

Plagioclase 

gneissic, por- gneissic 

phyroblastic 

Discrete sub- Lacks magnetite 

hedral zoned and sphene 

epidote with 

cores of allanite 

Anomalous blue Anomalous brown/ 

birefringence blue birefringence 

Light brown/ 

brownish green/ 

green; anhedral 

Anhedral to subhedral; weakly 

zoned, normal; 

partly altered 

to epidote and 

sericite± 

calcite 

Light brown/ 

greenish brown/ 

brownish green; 

anhedral 

Anhedral to subhedral; weak to 

moderate zoning, 

continuous normal or oscillatory normal; 

partly altered to 

sericite±epidote 

and calcite 

Primary sphene Discrete Rare, mostly 

interstitial 

grains 

euhedral/subhedral grains 

Lemon Creek 

Glacier 

47-52 

49.8 

15-22 

17.2 

0-5 

1.2 

21 .38 

31.8 

Hornblende 

Tonalite 

Quartz monzodiorite 

Apatite 

32-40 

38 

Foliated, 

gneissic, 

linea ted 

Mafic rich; 

lacks sphene 

Anomalous blue 

birefringence 

Light brown/ 

greenish brown/ 

brownish green; 

anhedral 

Anhedral; weak 

zoning, continuous 

normal ; partly 

altered to serici te±epidote 

and calcite 

Rare/absent 

Mendenhall 

Glacier 

50-61 

53.5 

15-23 

19.5 

1-5 

2.0 

21-32 

25.1 

Hornblende 

Tonalite 

Quartz diorite? 

Sphene, apatite 

38-46 

41 

Foliated, 

lineated, 

equigranular 

Magnetiteapatite clots; 

euhedral sphene 

Anomalous brown 

birefringence 

Light brown/ 

greenish brown/ 

green; subhedral 

Subhedral; moderate to weak multiple zoning, oscillatory normal; 

partly altered to 

serici te±epidote 

Taku Cabin 

51-62 

56.8 

17-25 

21.7 

1-5 

2.7 

15-23 

18.8 

Hornblende 

Tonalite 

Granodiorite 

Sphene 

34-41 

38 

Foliated, 

equigranular 

Magnetiteapatite clots; 

subhedral sphene 

Anomalous brown 

birefringence 

Light brown/ 

greenish brown/ 

brownish green; 

subhedral 

Subhedral; strong 

multiple zoning, 

oscillatory normal; 

partly altered to 

sericite±clinozoicite 

Annex Lakes 

29-61 

50.4 

8-35 

21.6 

1-23 

14.4 

5-27 

13.6 

Biotite 

Granodiorite 

Tonalite, granite, 

quartz monzodiorite 

Sphene, allanite 

24-45 

33 

Foliated, weakly 

gneissic to inequigranular 

Very heterogeneous; 

K-feldspar phenocryst 

Anomalous brown/ 

blue birefringence 

Light brown/ 

brownish green/ 

green; subhedral 

Subhedral; weakly 

zoned, continuous 

normal; partly 

altered to serici te±epidote and 

calcite 

Discrete euhedral Euhedral inclusions; Discrete euhedral/ 

grains and anhedral anhedral interstitial subhedral grains and 

interstitial and and subhedral inter- anhedral interstitial/ 

intergrowths with 

mafic minerals 

growths with mafic 

minerals 

inter granular 

12 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
(/) 

Q) ... Q) Q) 

(/) C'V "0 "0 

~ Q. c X * Q) 

C) (/) Q) 0 Q) Q) c 

0 N ~ Q) Q) - - - Q) 

- .0 - c Q) 0 X 

Ol ... Q) c - f- Q) c "0 c 0 

C'V C'V Ll.. .... 0 I .J::. ... C'V ... :J I 0 Q) Q. C'V Q. >. Q.. 0 ~ I co Ll.. (/) <.:) w <( 0.. 

Mount I I I I I I 

Juneau I I I I I I I I I I I I 

Carlson I I I 

I I I I 

I I I I Creek I I I I 

I I I I 

I I 

lemon Creek I I 

I I 

Glacier I I 

I I 

Mendenhall I I 

Glacier I I . I I 

I 

Taku Cabin I 

I 

I I I I I 

Annex lakes I I I I 

I 

I 

I I I I 

Figure 4. Mineral occurrences in large sills east of Juneau. Solid line, mineral occurs in all or nearly all thin 

sections; long dashed line, mineral occurs in most thin sections; short dashed line, mineral occurs sporadically 

in some or in many thin sections; dotted line, mineral occurs rarely and in only a few thin sections. Epidote* 

is coarse, well formed, subhedral, and primary-appearing. Hornblende includes all primary and secondary 

green and brown amphiboles. Accessory apatite and zircon occur in all or most rocks. 

Figures 3-23; Tables 1-11 13 
C/) 

w 

....J 

a. 

~ 

CJ3 

LJ.. 

0 

a: 

w 

co 

~ 

:::> 

z 

C/) 

w 

....J 

a. 

~ 

<t: 

C/) 

LJ.. 

0 

a: 

w 

co 

~ 

:::> 

z 

C/) 

w 

....J 

a. 

:2: 

CJ3 

LJ.. 

0 

a: 

w 

co 

:2: 

::l 

z 

12,-------------------------------------~ 

10 

8 

6 

4 

2 

0 

Mount Juneau 

pluton 

6 10 14 18 22 26 30 34 38 42 

RANGE OF COLOR INDEX 

12,---------------------------------------, 

10 Mendenhall Glacier pluton 

8 

6 

4 

2 

0 +---......... ----.----. 

10 14 18 22 26 30 34 38 42 

RANGE OF COLOR INDEX 

12~------------------~ 

10 Lemon Creek Glacier pluton 

8 

6 

4 

6 1 0 14 1 8 22 26 30 34 38 42 

RANGE OF COLOR INDEX 

12~--------------------------------------, 

C/) 

w 

....J 

10 

~ 8 

<t: 

C/) 

LJ.. 

0 6 a: 

w 

co 

~ 4 

z 

2 

Carlson Creek pluton 

10 14 18 22 26 30 34 38 42 

RANGE OF COLOR INDEX 

12~--------------------, 

C/) 

w 

....J 

a. 

:2: 

<t: 

C/) 

IJ... 

0 

a: 

w 

co 

:2: 

::l 

z 

10 Annex Lakes pluton 

6 1 0 1 4 1 8 22 26 30 34 38 42 

RANGE OF COLOR INDEX 

12~------------------------------------~ 

10 

8 

6 

Taku Cabin pluton 

6 1 0 14 18 22 26 30 34 38 42 

RANGE OF COLOR INDEX 

Figure 5. Distribution of color index (percentage of mafic minerals) in large sills east of Juneau. Numbers on horizontal axis 

(range of color index) correspond to midpoints of range. 

14 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
(/) 

L.U 

....J 

c.. 

::2: 

<( 

(/) 

u. 

0 

a: 

w 

c:l 

::2: 

:::> 

z 

CJ) 

L.U 

....J 

c.. 

::2: 

<( 

CJ) 

u.. 

0 

a: 

L.U 

c:l 

::2: 

:::> 

z 

CJ) 

L.U 

....J 

c.. 

:::2: 

<( 

CJ) 

u.. 

0 

a: 

L.U 

c:l 

::2: 

:::> 

z 

8 

6 

4 

2 

30 

Mount Juneau 

pluton 

32 34 36 38 40 42 

An CONTENT, IN PERCENT 

44 

8~------------------------------------~ 

6 

4 

2 

0 

8 

6 

4 

2 

Mendenhall 

pluton 

30 32 34 36 38 40 42 

An CONTENT, IN PERCENT 

Lemon Creek Glacier 

pluton 

30 32 34 36 38 40 

An CONTENT, IN PERCENT 

44 46 

42 44 

CJ) 

L.U 

....J 

c.. 

::2: 

<( 

CJ) 

LL 

0 

a: 

L.U 

c:l 

::2: 

:::> 

z 

CJ) 

L.U 

....J 

c.. 

::2: 

<( 

CJ) 

u.. 

0 

a: 

L.U 

c:l 

::2: 

:::> 

z 

CJ) 

L.U 

....J 

c.. 

::2: 

<( 

CJ) 

u.. 

0 

a: 

L.U 

c:l 

::2: 

:::> 

z 

8 

6 

4 

2 

Carlson Creek 

pluton 

30 32 34 36 38 40 42 44 46 

An CONTENT, IN PERCENT 

8~------------------------------------~ 

Annex Lakes pluton 

6 

4 

2 

0 

24 26 28 30 32 34 36 38 40 42 44 46 

AnCONTEN~INPERCENT 

8 

Taku Cabin pluton 

6 

4 

2 

30 32 34 36 38 40 42 44 

An CONTENT, IN PERCENT 

Figure 6. Distribution of anorthite (An) composition, in percent, in large sills east of Juneau. Numbers on horizontal axis (An 

content) correspond to midpoints of range. Anorthite content estimated optically by Michel-Levy method. 

Figures 3-23; Tables 1-11 15 
1-

z 

w 

0 

ffi 50 

a. 

z 

c: 

<( 

w 

> 

t= 

<( 

:!: 

a: 

0 

z 

40 

30 32 34 36 38 40 42 

OPTICALLY MEASURED An, IN PERCENT 

Figure 7. Normative An content plotted against optically measured An 

content for samples from large sills east of Juneau. Each box represents 

one sample for which normative chemistry was determined and An content 

was optically measured. Line is best fit line based on simple regression 

equation. 

16 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
Table 3. Average major-element chemistry for plutonic sills east of Juneau 

[Results in weight percent. Std. dev., standard deviation; Norm, normative; CI, color index; An, anorthite 

content of plagioclase; ---, not applicable] 

Pluton - - - - Mount Carlson Creek Lemon Creek Mendenhall Taku Cabin Annex 

Juneau Glacier Glacier Lakes 

Average Std. Average Std. Average Std. Average Std. Average Std. Average Std. 

dev. dev. dev. dev. dev. dev. 

Si02 59.82 4.37 60.07 2.85 56.84 2.77 61.32 1.98 61.62 .08 65.59 4.03 

Al 2o3 18.40 .85 17.88 .78 18.02 1. 68 17.57 . 60 16.95 .04 17.30 .81 

Fe2o3 2.06 .52 1.56 .97 2.10 . 65 1. 99 .50 2.57 .13 1. 49 . 61 

FeO 4.09 1. 70 4.47 1.13 5.40 1. 28 3. 71 .77 3.77 .18 2.15 1. 03 

MgO 2.49 1.10 2.94 .55 3.47 .86 2.70 .58 2.73 .07 1.38 .76 

CaO 6.58 1. 07 6.69 .92 7. 73 .86 6.66 .47 6.26 .06 4.67 1.17 

Na2o 3.77 .43 3.62 .16 3.67 . 31 3.59 .20 3.36 .03 4.38 . 83 

K2o 1. 64 . 70 1. 57 .38 1. 45 .28 1. 36 .40 1.72 .06 2.23 1.01 

Ti02 .73 .30 .81 .15 . 83 .26 .72 .11 .68 .47 .25 

P205 .29 .08 .28 .06 .36 .11 .28 .03 .23 .23 .15 

MnO .12 .04 .11 . 02 .14 .03 .1 0 .02 .13 .09 . 03 

Norm CI 16.4 6.16 18.4 3.40 22.0 4.30 16.6 3.19 17.2 9.2 4.52 

Norm An 47.1 4.85 47.6 2.80 46.8 6.10 47.8 .85 47.8 . 42 35.6 8.56 

Number of 

samples 12 12 10 10 7 7 9 9 2 2 10 10 

Table 4. Chemical characteristics of plutonic sills east of Juneau 

[Results in weight percent. Feo*, total iron; A/CNK, molecular proportions of the ratio 

Al 0~/CaO+Na 0+K 0; avg., average; DI, differentiation index--sum of normative quartz, orthoclase, 

albi e, nepheline, and leucite; Alk/lime, K20+Na20/Ca0; --- . not applicable] 

Pluton - - - - - Mount Carlson Lemon Creek Mendenhall Annex Taku 

Juneau Creek Glacier Glacier Lakes Cabin 

Si02 53-64 57-66 51-60 57-64 60-69 62 

Al 2o3 18-19 16-19 15-20 17-19 16-18 17 

FeO * 3-9 4-7 7-9 4-7 2-6 6 

CaO 5-8 5-8 7-9 6-7 4-6 6 

K20+Na2o 4-7 5-6 5-6 4-5 5-8 5 

A/CNK 0.88-1.03 0.86-0.96 0.66-0.90 0.87-0.94 0.89-1.05 0.91 

(avg.) (0.94) (0.90) (0.83) (0.90) (0.95) 

DI 42-66 46-65 36-49 47-60 56-74 56 

(avg.) (56) (53) (42) (55) (68) 

Alk/lime 0.55-1.28 0. 63-1.21 0.51-0.74 0.65-0.89 0.93-1.80 0.80-0.83 

(avg.) (0.88) (0.82) (66) (0.75) ( 1. 33) 

Figures 3-23; Tables 1-11 17 
10 10 

0 + 

t 0 

·~ AO A 

0 

* ~ # 

0 0 "\.4 A 0 

Q) 5 A+ /I, ~5 u.. -6 o. 0 0 + + A 0 

<!lo o 

0 + "'fit- 0... 0 

A.A .. A 

0 <h* A A • o* + ~ 

0 0 

.... 50 60 70 50 60 70 

:z 

LlJ 

u 10 10 a:: 

LlJ 

Q.. 

.... 0 0 + 

X + •tt 0 G 

+ A + ~ 0 0 0 8 AA -~!,AM + + N o'l .A ~A A 

LlJ ~ + • + 0 + 

~ + l>.~ A~A 0 0 0 0 0 

0 5 •a -0 A A:fl A C'O 5 0 0 + , 0 

:z N + u C'O 

z 0 

.,:' 

:z 

LlJ 

.... 

:z 

0 

u 0 0 50 60 70 50 60 70 

LlJ 

0 

X 20 0 --rl I+ I I ,----r-T----r-r---r--r-r-r-r 5 --rr-rr I I I I I 

.~ A 0 0 EXPLANATION l:l. 0 A. ~ + + +- MJ 0 - LC 

• 0 '}}. A 0 

A * 91 6- MG 0 - AL 

0 A • ·- cc X- TC 

(V) N 0 

...0115 0 

<! 0 r--

·~ • 

0 rae~~ A~ A f' ()6. 0 0 0 6/!l) 0 

10 0 50 60 70 50 50 70 

Si02 Si02 

Si02 CONTENT, IN WEIGHT PERCENT 

Figure 8. Variation between Si02 and major oxides in large sills east of Juneau. MJ, Mount Juneau pluton; MG, Mendenhall 

Glacier pluton; CC, Carlson Creek pluton; LC, Lemon Creek Glacier pluton; AL, Annex Lakes pluton; and TC, Taku Cabin 

pluton. F~O*, total iron. 

18 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
Feo* 

EXPLANATION 

. - MJ 

'V- MG 

0- LC 

.A.- cc 

0- TC 

o- AL 

THOLEIITIC 

CALC-ALKALINE 

0 

ALK L---------------------------------------------------------------------------~ Mg 

Figure 9. AFM diagram with plots of samples from large sills east of Juneau. Boundary line from Irvine and Baragar 

(1971). MJ, Mount Juneau pluton; MG, Mendenhall Glacier pluton; LC, Lemon Creek Glacier pluton; CC, Carlson 

Creek pluton; TC, Taku Cabin pluton; and AL, Annex Lakes pluton. FeO*, total iron; ALK, Na20+ ~0. 

Figures 3-23; Tables 1-11 19 
An 

0 

TRONDHJEMITE GRANITE 

Ab 

EXPLANATION 

• MJ 

\l MG 

o LC 

& CC 

0 TC 

o AL 

Or 

Figure 10. Plots of normative Ab-Or-An (albite-orthoclase-anorthite) content of rocks from large sills east of Juneau. 

Boundary fields from Barker (1979). MJ, Mount Juneau pluton; MG, Mendenhall Glacier pluton; LC, Lemon Creek 

Glacier pluton; CC, Carlson Creek pluton; TC, Taku Cabin pluton; and AL, Annex Lakes pluton. 

20 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
Table 5. Organization of figures and tables with data on individual plutons 

-------------------·---------~---

Name of 

pluton 

Location 

map, 

figure No. 

QAP Descriptive 

diagram, summary, 

figure No . table No. 

------------------------

Mount Juneau 11 12 6 

Mendenhall 13 14 7 

Glacier 

Lemon Creek 15 16 8 

Glacier 

Carlson Creek 17 18 9 

Annex Lakes 1 9 20 10 

Taku Cabin 21 22 11 

Petrographic 

data, 

table No. 

6A 

7A 

8A 

9A 

10A 

11 A 

Major-element 

chemistry, 

table No. 

68 

7B 

88 

98 

1 OB 

11 B 

---------- ----- Explanation of abbreviations in tables of petrographic data: 

Accessory and secondary minerals (reported in tables in order of 3.bundance): 

al, allanite em, cummingtoni te pr' prehni te 

ap, apatite ep, epidote px, pyroxene 

ca, calcite ga' garnet se, sericite 

chl, chlorite mu, muscovite sp, sphene 

cl z, cl inozoi site opq, opaques zi, zi. rcon 

Abbreviations that begin with upper case letters in tables indicate an 

abundance of that mineral greater than a trace amount, that is, greater 

than 1 percent. 

Main textures: 

Al, allotri amorphi c Gn, gneissic Ln, lineated 

Au, augen Gr, granular Pb, por phyro blastic 

Eg, e qui granular Hy, hypidiomorphic Pc, protoclastic 

Eq, equant Iq, inequigranular Pp' porphyritic 

Fo, foliated La, layered Se, seriate 

Mineral abundance determined by visual estimation: tr, trace (less than 1 

percent); min, minor (1-5 percent); uncom, uncommon (5-10 percent); com, 

common (10-40 percent); abnt, abundant (greater than 40 percent). 

Form of primary sphene: eu, euhedral; sbh, subhedral; an, anhedral. 

Figures 3-23; Tables 1-11 21 
58° 

20' 

0 2 3 4 KILOMETERS 

134°05' 

X 

Figure 11. Geologic sketch map of the Mount Juneau pluton, showing sample locations. Samples 8 through 12 shown as a 

traverse line across pluton. Fault indicated by heavy line; contact dashed where approximately located. 

22 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
QM 

MO 

Alkali feldspar Plagioclase feldspar 

Figure 12. Compositional modes of selected 

samples from the Mount Juneau pluton plotted on plutonic rock classification diagram of 

Streckeisen (1973). Several pairs plot in same 

place. Average modal composition shown by 

dark triangle. GR, granite; GD, granodiorite; 

TO, tonalite; OM, quartz monzonite; 00, 

quartz monzodiorite; QD, quartz diorite; MO, 

monzonite; MD, monzodiorite; and Dl, diorite. 

Table 6. Petrographic and major-element chemical data for the Mount Juneau pluton 

Major rock type: 

Gneissic garnet- and sphene-bearing hornblende-biotite tonalite 

Minor rock types: 

Gneissic hornblende-biotite granodiorite and biotite-hornblende quartz diorite 

Location: 

East of Juneau and west of Taku Inlet 

Age: 

90(?) Ma (metamorphosed and deformed about 65? Ma) 

Description: 

Light to medium gray, and brownish gray to grayish brown, homogeneous to heterogeneous, medium to coarse 

grained and locally fine grained, foliated and locally lineated, gneissic and porphyroblastic to inequigranular. 

Biotite generally more common than hornblende. Typically contains medium- to coarse-grained, anhedral, 

augen-shaped plagioclase and hornblende; medium-grained anhedral granular quartz; medium-grained, lamellar 

biotite; intergranular quartz and K-feldspar; and minor but conspicuous rounded garnet, euhedral sphene, and 

subhedral primary-appearing epidote. Color index range 10-37, color index average 23 

Comments: 

Locally heterogeneous, most deformed and metamorphosed of Juneau sill bodies; exhibits most diverse and 

variable mineralogy of sill bodies. Pluton partly cuts across regional structure and isograds (Ford and Brew, 1973). 

Contains subhedral zoned epidote similar to the primary magmatic epidote described by Zen and Hammarstrom 

(1984) 

(Table continued on next page.) 

Figures 3-23; Tables 1-11 23 
Table 6. Petrographic and major-element chemical data for the Mount Juneau pluton-Continued 

A. Petrographic data 

[Results in percent. Plg, plagioclase; Qtz, quartz; K-f, K-feldspar; Hbl, hornblende; Bio, biotite; An, anorthite content of plagioclase; 

n.d., not determined. See table 5 for other abbreviations] 

Map Sample Plg Qtz K-f 

No. No. 

Mafic Hbl 1 

minerals 

Epidote 1 • 2 Chlorite 1 Accessory Percent 

minerals accessories 

Secondary 

minerals (fig. 

11) 

8008022 60.8 16.8 

8008023 63.2 18.4 

820B327c 61.1 25.0 

820B327d 62.5 20.5 

8208331 52. 1 24.5 

85SD119 56.1 19.6 

85WN070 59.3 17.3 

71AF117 54.7 14.9 

71AF116 57.0 18.1 

1 0 71 AF11 5 55. 6 21 . 6 

11 71AF114 51.6 23.1 

12 71AF113 52.2 17.4 

13 71AF130 52.9 20.6 

14 71AF132 55.8 20.3 

15 71AF134 54.8 16.0 

16 71AF135 55.1 15.3 

17 71AF137 52.7 20.3 

18 71AF138 49.4 13.2 

19 71AF145 47.3 19.8 

20 71AF144 48.9 19.5 

21 71AF143 50.6 18.9 

223 71AF141 44.0 14.8 

23 64AF201 59.6 16.9 

24 64AF229 48.0 22.0 

25 

26 

27 

28 

29 

303 

64AB044 56.5 5. 9 

64AB043 61.4 6.7 

64AB040 53.8 11.4 

64AB039 65.0 12.0 

64AF036 48.7 23·.2 

64AF035 62.3 tr 

Average 55.2 17.8 

Standard 

deviation 4.9 

Nwnber of 

samples 28 

4.7 

28 

1.3 21.1 n.d. 

8. 9 9. 5 min 

7.6 36.3 uncom 

11.8 35.2 uncom 

12.6 10.8 uncom 

4. 8 19.5 uncom 

7. 6 15.8 com 

.2 30.2 4. 9 

.1 24.4 n.d. 

2.4 20.4 tr 

1 .8 23.5 tr 

1. 9 27.4 tr 

4. 6 21.4 tr 

2. 3 21.2 1. 5 

3.2 25.0 2. 8 

5.9 23.2 6. 2 

5. 0 21.5 2. 6 

1.7 34.0 18.1 

9. 3 22.6 19.7 

10.8 20.8 8. 5 

8.8 21.7 8. 7 

4.6 36.6 15.8 

5.1 18.4 5. 8 

17.0 13.0 6.0 

29.0 15.7 

0 25.2 18.9 

1.2 33.6 21.7 

23.0 1. 2 

• 7 27.4 1.3 

0 37.7 33.8 

4.9 22.5 7.0 

4.6 6. 0 6.8 

28 26 23 

com 

min 

min 

min 

min 

com 

min 

24.4 

17.1 

18.2 

20.0 

22.1 

18.6 

17.5 

19.7 

15.2 

17.1 

10.5 

12.0 

11.1 

12.1 

17.1 

12.4 

6. 7 

1.7 

10.7 

21 .8 

25.4 

1.6 

15.4 

6.0 

23 

min 

min 

tr 

tr 

min 

tr 

tr 

16.0 

13.7 

10.4 

12.9 

13.6 

7.6 

10.6 

11.9 

6.1 

8. 4 

10.0 

3. 5 

4.1 

4. 9 

10.8 

6. 2 

3.0 

.4 

. 7 

. 7 

.2 

• 3 

n.d. 

7.1 

5.1 

23 

tr 

tr 

tr 

tr 

tr 

tr 

min 

tr 

2. 3 

1.8 

2.2 

2. 6 

2.3 

1.9 

1.0 

1.2 

1.3 

3. 5 

• 4 

• 9 

. 3 

2. 5 

tr 

tr 

• 7 

min 

1.2 

n.d. 

.4 

. 7 

1.3 

.9 

23 

Ga,ap min 

Ga,Sp min 

Ga,sp,ap,zi min 

. Ga,sp,ap,zi min 

Sp,ap,zi min 

ap,al tr 

Sp ,ap, zi min 

Ga,ap,sp,opq 1.0 

Ga,ap,al 5.0 

ga ,ap,zi • 4 

Ga,Sp,ap,zi,opq 1.3 

Ga,sp,ap,opq 2.6 

Ga,opq,al,sp,ap .5 

ga,sp,al,ap .2 

Ga ,sp ,ap ,opq 1 . 4 

Ga,sp,ap,al,opq .5 

Ga,al,ap,sp .5 

Ga,ap,sp,al,opq 1.7 

Ga,ap,al,sp .5 

ga,sp,opq,ap .4 

Ga ,sp ,ap ,al . 7 

Ga,sp,al 1.3 

opq ,ap ,sp . 2 

sp,opq .3 

Ga ,opq ,ap, zi 5.0 

Ga ,opq ,ap 4.5 

ap ,zi ,opq tr 

ap,zi tr 

sp,ap,zi • 4 

opq,sp 1.6 

Results reported in letter abbreviations (com, tr, etc.) are from this study (see table 5 for explanation of 

abbreviations). Results report<pd in volwne percent were point counted from thin sections in an earlier 

study (Ford and Brew, 1981) and are not always consistent with the total mafic mineral percentages reported 

in this study. 

Includes clean and well-developed subhedral grains that appear primary. 

Not counted in averages. 

24 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 

Ep 

ep 

ep,mu 

ap,se 

ep,sp 

ep,mu 

ep,mu,ca 

Se ,opq 

mu,sp 

mu,sp 

mu,sp 

mu,sp 

mu,ca 

mu,pr ,ca 

ca,se 

mu,pr,ca 

mu ,sp ,ca 

Ca,sp 

sp ,opq 

se,opq 

sp,opq 

sp,se 

se,sp 

mu,sp 

pr,sp,se 

sp,ca,se 

mu ,sp ,opq 

mu,sp 

se,sp 

mu,sp 

Main 

texture 

Pb-Pc-Gn 

Pb-Gn 

Gn-La 

Gn-La 

Gn-La 

Au-Iq 

Gn 

Fo-Gn-Pb 

Fo-Gn-Pb 

Fo-Gn-Pb 

Fo-Gn-Pb 

Fo-Gn-Pb 

Fo-Gn-Pb 

Fo-Gn-Au 

Fo-Gn-Au 

Fo-Gn-Au 

Fo-Gn-Au 

Fo-Gn 

Fo-Gn-Pb 

Fo-Gn-Au 

Fo-Gn-Pb 

Fo-Gn 

Fo-Gn 

Fo-Gn 

Fo-Gn 

Fo-Ln-Gn 

Fo-Gn-Ln 

Fo-Ln 

Fo-Gn 

Fo-Al-Gr 

An 

n.d. 

n.d. 

32 

n.d • 

32 

37 

35 

n.d. 

n.d. 

n.d. 

n.d. 

n.d. 

n.d. 

n.d. 

36 

40 

37 

n.d. 

39 

36 

37 

n.d. 

39 

n.d. 

39 

40 

37 

32 

40 

n.d. 
Table 6. Petrographic and major-element chemical data for the Mount Juneau pluton-Continued 

B. Major-element chemical data 

[Samples were analyzed in laboratories of the U.S. Geological Survey by rapid-rock methods or by xray fluorescence. FeO was determined by wet chemical methods. Results normalized to 100-percent 

volatile free; percentages may not add up exactly to 100.00 because oxide and norm values were 

rounded off from three to two decimal places. LOI, loss on ignition (H2

0 and co2); Norm, 

normative; CI, color index; An, anorthite content of plagioclase; DI, differentiation index--sum of 

normative quartz, orthoclase, albite, nepheline, and leucite; n.d., not determined] 

Sample No.---80DB 

022 

Map No.------

(fig. 11) 

Si02 

Al 2o3 

Fe 2o3 

FeO 

MgO 

cao 

Na2o 

K2o 

Ti0 2 

P205 

MnO 

LOI 

Quartz 

Orthoclase 

Albite 

Anorthite 

Diopside 

Hypersthene 

Magnetite 

Ilmenite 

Apatite 

Norm CI 

Norm An 

DI 

61.38 

18.06 

2.11 

3.65 

2.03 

6.50 

3.20 

2.08 

.56 

.27 

.15 

.59 

17.04 

12.29 

27.04 

28.79 

1.39 

8.70 

3.06 

1. 08 

.63 

14.2 

51.6 

56.4 

80DB 

023 

2 

65.36 

17.73 

1. 31 

2.23 

1.29 

5.02 

4.19 

2.24 

.37 

.17 

.1 0 

.52 

19.25 

13.23 

35.41 

22.99 

.63 

5.49 

1. 90 

.69 

.40 

8.7 

39.4 

67.9 

76BJ 

008 

21 

64DB 64DB 

039 040 

28 27 

64DB 

043 

26 

64DB 

044 

64AF 

201 

64AF 

229 

87JS 

007 

76AF 

030 

71AF 

1 37 

--------------------------------- 25 23 24 31 32 17 

Whole-rock analyses (weight percent) 

62.42 

17.64 

1. 94 

3.47 

1.73 

6.32 

3.47 

2. 14 

.53 

.21 

.12 

1. 04 

17.45 

12.66 

29.34 

26.25 

3.07 

6.92 

2.81 

1. 01 

.50 

13.8 

47.2 

59.5 

61.45 

18.05 

3.45 

1. 93 

2.43 

5.58 

4.46 

1. 52 

. 80 

.26 

.06 

55.27 55.29 52.97 

18.80 

2.15 

5.72 

3.88 

7.25 

4.19 

1. 23 

1.00 

.39 

. 13 

19.60 

1. 51 

6.03 

3.52 

7.94 

4.02 

.33 

1. 21 

.39 

.15 

19.94 

2.32 

7.05 

3.83 

7.45 

4.03 

.79 

1.11 

.36 

.17 

61.24 63.94 

17.92 17.84 

2. 02 1. 82 

3.85 2.64 

2. 02 1. 42 

6.58 5.07 

3.34 3.85 

2.02 2.64 

. 60 . 48 

. 29 . 23 

.12 .08 

62.32 

17.89 

2. 01 

3.28 

1.72 

7. 01 

3.06 

1.73 

.49 

.34 

.15 

53.19 63.06 

19.60 

2.14 

6. 13 

4.39 

8.37 

3.78 

.85 

1.12 

.33 

.11 

17.73 

1. 94 

3.06 

1. 63 

5. 91 

3.67 

2. 14 

. 52 

.24 

.11 

. 78 1. 59 . 61 .96 .80 . 98 .65 1.14 n.d . 

CIPW norms (weight percent) 

15.11 

8.99 

37.75 

24.73 

.95 

5.62 

4.09 

1. 52 

. 61 

3.64 6.30 1.68 16.28 

7. 24 1 . 96 4. 64 11 . 98 

35.44 34.03 34.01 28.26 

28.87 34.46 34.00 27.91 

3.76 1.96 .49 2.32 

15.15 15.91 18.80 8.53 

3.11 

1. 90 

.90 

2.19 

2.29 

. 91 

3.36 2.94 

2.10 1.13 

.84 .68 

12.8 23.9 

39.6 44.9 

61.9 46.3 

22.4 24.8 14.9 

50.3 49.9 49.7 

42.3 40.4 56.5 

17.93 20.08 

15.57 n.d. 

32.58 10.21 

23.60 25.89 

. 01 2.17 

6.22 7.05 

2.65 2.92 

. 91 . 93 

.54 .78 

9. 8 13.1 

42.0 53.7 

66.2 56.2 

2.01 18.34 

5.01 12.64 

31.96 31.03 

34.02 25.59 

4.40 1.75 

16.61 6.56 

3.11 2. 81 

2. 13 . 99 

.77 .57 

26.2 

51.6 

39.0 

12.1 

45.2 

61.7 

Figures 3-23; Tables 1-11 25 
6• 

7• 

134°25' 

\ 

\ 

I 

I 

I 

I 

I 

I 

I 

1 Norris 1 Glacier 

Mendenhall Glacier pluton 

" 

\. \.. " \ 

\.\..~ 

\\..\..~ " 

1• 

\. \.. \.. \.. 

\. \.. \.. \.. \.. \.. Mendenhall Glacier pluton 

\..\..\..\..\:\..\: 

\..\.\..\..\..\. 

\..\.\..\..\..\..\.. \.. \.. 

3• 

4• 

2• 

/ 

' / ' •8 I 

' / Gneiss 

/ ' 

' / 

'- '- '- '- '- \. '- '- \.. \.. '- '- '- Schist '- '- '- \. '- / , 

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~\ I / 

\.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \..~-' 

\..\..\.\..\..\..\..\..\..\..\.\..\..\..\..\..\..\..\.\..\..\..\..\..\..\..~ 

\.. \.. \.. \.. \. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \; 

58°25' \.. \.. \. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.. \.: 

0 2 3 4 KILOMETERS 

' 

/ 

' I 

/ 

' 

/ 

' 

/ 

' 

/ 

Figure 13. Geologic sketch map of the Mendenhall Glacier pluton, showing sample locations. Sample 

localities 5 and 9 not shown on map; they are located on western side of Mendenhall Glacier. Contacts 

dashed where approximately located. 

26 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
GR 

QM 

MO 

Alkali feldspar Plagioclase feldspar 

Figure 14. Compositional modes of selected 

samples from the Mendenhall Glacier pluton 

plotted on plutonic rock classification diagram 

of Streckeisen (1973). Average modal composition shown by dark triangle. GR, granite; 

GD, granodiorite; TO, tonalite; QM, quartz 

monzonite; QO, quartz monzodiorite; QD, 

quartz diorite; MO, monzonite; MD, monzodiorite; and Dl, diorite. 

Table 7. Petrographic and major-element chemical data for the Mendenhall Glacier pluton 

Major rock type: 

Sphene-bearing biotite-hornblende tonalite 

Minor rock type: 

Quartz diorite (lower border phase) 

Location: 

Northeast of Juneau and east of Mendenhall Glacier 

Age: 

55 to 60 Ma 

Description: 

Medium to light gray, homogeneous, medium to coarse grained, foliated and lineated, locally inequigranular to 

gneissic. Hornblende more common than biotite. Composed of medium- to coarse-grained, subhedral plagioclase 

and elongated hornblende; medium-grained tabular biotite; fine- to medium-grained, anhedral intergranular 

quartz; some coarser granular quartz; and fine- to medium-grained, interstitial K-feldspar. Conspicuous subhedral 

sphene and subhedral epidote locally common. Color index range 21-32, color index average 25 

Comments: 

Subhedral primary-appearing epidote present in more deformed and metamorphosed border-phase rocks. Very 

uniform and homogeneous pluton; many features are similar to Taku Cabin pluton. Garnet present in one sample 

(Table continued on next page.) 

Figures 3-23; Tables 1-11 27 
Table 7. Petrographic and major-element chemical data for the Mendenhall Glacier pluton-Continued 

A. Petrographic data 

[Results in percent. An, anorthite content of plagioclase; QD, quartz diorite; TO, tonalite; n.d., not determined; not 

present. See table 5 for other abbreviations] 

Map 

No. 1 

(fig. 

13) 

2 

3 

QD 

TO 

TO 

TO 

QD 

TO 

TO 

TO 

TO 

TO 

Sample 

No. 

Plagio- Quartz 

clase 

K-feld- Mafic 

spar minerals 

87SK096 

87SK097 

87RK173 

87Ar1 02 

80SK120 

87RK177 

87SK1 01 

65Bd276 

65Bd284 

65Bd293 

65AF243 

65Ar248 

65Ar263 

53.6 

49.8 

54.6 

52.4 

49.8 

61.0 

abnt 

abnt 

abnt 

abnt 

abnt 

abnt 

abnt 

abnt 

65AF265 abnt 

65AF266 abnt 

Average 53.5 

Standard 

deviation 4.2 

Number of 

samples 6 

21.5 2.1 22.7 

21.2 5.0 24.1 

22.8 .2 22.5 

18.0 2.2 27.5 

15.7 2.1 32.4 

17.7 .3 21 .1 

uncom tr 25 

com min 25 

com tr 25 

com tr 25 

uncom tr 30 

com min 20 

com min 25 

com tr 25 

com tr 16 

com tr 20 

19.5 2.0 25.1 

2.8 1.7 4.2 

Hornblende 

com 

com 

com 

com 

uncom3 

com 

com 

com 

com 

com 

com 

com 

Biotite 

uncom 

uncom 

uncom 

com 

com 

uncom 

com 

uncom 

com 

com 

uncom 

uncom 

uncom 

com 

uncom 

uncom 

Opaques Sphene 

min tr-sbh 

min min-eu 

min tr-sbh 

min min-eu 

tr tr-sbh 

min tr 

min 

min tr-sbh 

min min-eu 

min 

min tr-sbh 

min min-an 

tr min-eu 

tr 

min tr-sbh 

min tr-sbh 

Rock name rather than map number reported where no modal analysis was done. 

2 Most abundant mafic mineral. 

3 Altered to epidote and cummingtonite. 

Accessory 

minerals 

ap,al ,zi 

ap,zi 

ap,al,zi 

ap,zi 

ep,ap,zi 

ep,ap,al 

ep,ap,px 

ap,zi 

ap ,zi 

ap,zi 

ap, zi 

ap,zi 

ap,zi,al 

Ga,ap,zi 

ap ,zi 

ap,zi,al 

28 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 

Secondary 

minerals 

chl ,ep, pr ,sp 

chl ,ep,sp,pr 

chl,ep,sp,se 

chl,ep,sp,pr 

ep,sp 

ep,sp,chl 

sp,opq,ep 

chl,ep,pr 

chl,ep,sp,pr 

chl ,se 

chl,se,sp,pr 

chl ,ep,sp 

chl,ep,sp,se 

chl ,ep ,em 

chl,pr,ep,sp 

chl,ep,pr ,sp 

Main 

texture 

Fo-Hy-Iq 

Fo-Ln-Iq 

Fo-Hy-Iq 

Fo-Ln-Iq 

Fo-Gn-Ln 

Fo-Ln-Iq 

Fo-Ln-Eg 

Fo-Ln-Iq 

F'o-Ln-Eg 

Fo-Ln-Eg 

Fo-Iq 

Fo-Ln-Eg 

Fo-Ln-Iq 

Fo-Ln-Gn 

Fo-Iq 

Fo-Ln 

An 

41 

40 

45 

39 

n.d. 

39 

n.d. 

41 

40 

41 

n.d. 

46 

40 

n.d. 

40 

38 
Table 7. Petrographic and major-element chemical data for the Mendenhall Glacier 

pluton-Continued 

B. Major-element chemical data 

[Samples were analyzed in laboratories of the U.S. Geological Survey by x-ray 

fluorescence. FeO was determined by wet chemical methods. Results normalized 

to 100-percent volatile free; percentages may not add up exactly to 100.00 

because oxide and norm values were rounded off from three to two decimal 

places. LOI, loss on ignition (H2o and C0 2); Norm, normative; CI, color 

index; An, anorthite content of plagioclase; DI, differentiation index--sum of 

normative quartz, orthoclase, albite, nepheline, and leucite] 

Sample No.---87777 

(JS37) 

Map No.------ 7 

(fig. 13) 

Si02 

Al 2o3 

Fe2o3 

FeO 

MgO 

CaO 

Na 2o 

K20 

Ti0 2 

P205 

MnO 

LOI 

Quartz 

Orthoclase 

Albite 

Anorthite 

Diopside 

60.54 

17.02 

2.64 

4.24 

3.00 

6.00 

3.38 

1. 97 

.85 

. 24 

.11 

.60 

15.29 

11.67 

28.55 

25.47 

2.22 

Hypersthene 10.80 

Magnetite 3.83 

Ilmenite 1.61 

Apatite .56 

Norm CI 18.5 

Norm An 47.2 

DI 55.5 

80SK 87AF 87SK 87SK 87SK 87RK 87RK 87RK 

120 102 096 097 1 01 1 72 1 73 1 77 

6 5 2 8 3 4 9 

Whole-rock analyses (weight percent) 

59.68 62.93 

18.11 

2.37 

3.89 

3.00 

6. 61 

3.68 

1. 42 

.84 

.29 

.11 

. 41 

16.51 

.99 

4.45 

2.76 

6.18 

3.19 

2. 01 

. 63 

.23 

.11 

.54 

61.83 

17.56 

2.29 

3.33 

2. 51 

6.74 

3.70 

. 90 

.73 

. 31 

.1 0 

1. 01 

62.46 

17.43 

2.12 

3.13 

2. 21 

6.76 

3.47 

1. 39 

.63 

. 31 

.1 0 

.39 

60.80 

18.51 

2.29 

2.98 

2. 41 

7.24 

3.77 

.94 

.67 

.29 

.09 

.39 

64.05 

17.55 

1. 65 

2.75 

2. 01 

6.25 

3.74 

1.11 

.57 

.24 

.07 

.29 

CIPW norms (weight percent) 

13.68 17.93 

8. 37 11.90 

31.15 27.01 

28.70 24.78 

1.75 3.61 

10.65 

3.43 

1. 60 

.68 

17.4 

47.9 

53.2 

11 .60 

1. 43 

1. 21 

.54 

17.8 

47.9 

56.8 

18.70 19.43 

5.34 8.22 

31.27 29.32 

16.46 21.37 

5.56 6.56 

31.93 31.66 

28.67 27.89 30.80 27.81 

2.26 2.93 2.60 1.33 

8.35 7.23 

3.33 3.07 

1. 39 1 .19 

. 71 • 72 

15.3 14.4 

47.8 48.8 

55.3 56.9 

7.40 

3.32 

1. 27 

.70 

14.6 

49.1 

53.9 

7.24 

2. 40 

1. 07 

.56 

12.0 

46.8 

59.6 

62.15 57.40 

17.43 18.03 

1.63 1.90 

3.54 5.10 

2.44 3.95 

6.75 7.40 

3.69 3.72 

1. 33 1. 21 

.68 .85 

.29 . 32 

. 09 .13 

. 32 .15 

17.41 8.54 

7.86 7.14 

31.19 31.44 

27.07 28.94 

3.68 4.64 

8.47 

2.37 

1. 28 

.68 

15.8 

46.5 

56.5 

14.20 

2.76 

1. 61 

.75 

23.2 

47.9 

47.2 

Figures 3-23; Tables 1-11 29 
134°25' 

58°25' r---r-~ -/--,--/--,-/--,--/-.---,--/ -,--/--,--_, -,--/--,-,/--, -/-----, 

\. \.\ 

\. \. ~~ / ,_ \..\.\..\: 

\.\..\.\..\ 

\. \.. \.. \. \.. 

\..\.\.\..\.. 

\..\.\.\..\..\ 

' / ' 

' 

0 

'/ '/ '/ '/ '/ '/' I ~'~I - I -

/ '/\ / '/ / '/ 

- 1\(< _!.--- --...! Annex Lakes pluton 

' / ' ------~---X X 'y ' / ' / ' I -1 x/'-..., - I - I -

' ' X ' '..,_ ' / ' / 

I - X ' -

' X )(-~ / ' 

1 Lemon Creek Glacier pluton 1 x .. \ 1 -

' / X X , / 

' ' ' ' 

. 

_ _2( _ _) ' I 

'/ '/ '/ '/ '/ '/' -

/ ' / ' / ' Gneiss ' / ' / 

' ' 

' / ' / ' / 

Carlson Creek pluton 1 

~ - I -

~:\' / 

' 

2 3 4 KILOMETERS 

Figure 15. Geologic sketch map of the lemon Creek Glacier pluton, showing sample locations. Heavy 

line indicates fault. Contact dashed where approximately located. 

30 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
GR 

OM 

MO 

Alkali feldspar Plagioclase feldspar 

Figure 16. Compositional modes of selected 

samples from the Lemon Creek Glacier pluton plotted on plutonic rock classification diagram of Streckeisen (1973). Open circles are 

modes on border-phase rocks. Dots are 

modes on main-phase rocks (two samples 

plot in same place). Average modal composition of main phase shown by dark triangle. 

GR, granite; GD, granodiorite; TO, tonalite; 

QM, quartz monzonite; QO, quartz monzodiorite; QD, quartz diorite; MO, monzonite; MD, 

monzodiorite; and Dl, diorite. 

Table 8. Petrographic and major-element chemical data for the Lemon Creek Glacier pluton 

Major rock type: 

Biotite-hornblende tonalite 

Minor rock type: 

Sphene-biotite-hornblende quartz monzodiorite (border phase) 

Location: 

East of Juneau and northwest of Taku Inlet 

Age: 

65(?) to 70(?) Ma 

Description: 

Medium to dark or light gray, homogeneous to heterogeneous, medium to very coarse grained, foliated and 

lineated, gneissic, porphyroblastic to inequigranular, and weakly to strongly layered. Hornblende more common 

than biotite. Composed of medium to very coarse grained, porphyroblastic to augen-shaped, anhedral plagioclase; 

medium- to coarse-grained, tabular and elongated, anhedral hornblende; fine- to medium-grained, lamellar 

biotite; medium- to coarse-grained, anhedral stretched quartz and fine-grained, intergranular quartz, with 

intergranular K-feldspar. Color index range 21-38, color index average 32 

Comments: 

Lower and more deformed and metamorphosed border zone is more K-feldspar rich than main phase. Most mafic 

rich of the Juneau sill bodies. Locally contains garnet; main phase lacks sphene. One sample contains discrete 

subhedral primary-appearing epidote 

(Table continued on next page.) 

Figures 3-23; Tables 1-11 31 
Table 8. Petrographic and major-element chemical data for the Lemon Creek Glacier pluton-Continued 

A. Petrographic data 

[Results in percent. An, anorthite content of plagioclase; TO, tonalite; n.d., not determined; not present. See table 5 

for other abbreviations] 

Map Sample Plagio- Quartz K-feld- Mafic Horn- Biotite Opaques Sphene Accessory Secondary Main An 

No. 1 No. clase spar minerals blende minerals minerals texture 

(fig. 

15) 

86DB0472 59.5 16.8 12.3 11.4 uncom min min min-sbh Ap,zi chl ,ep,clz,se Fo-Gn-Pb 31 

2 86DB0472 57.3 13.0 16.8 12.9 com tr min min-sbh ap chl ,ep,se Fo-Gn-Pb n.d. 

86DB0.482 60.3 21.0 15.3 3.4 uncom min min tr-soh ap chl,ep,se Fo-Gn-Al-Gr n.d. 

86DB0492 69.4 9.1 10.5 11.0 com tr min min-sbh ap ep,se ,ca Fo-Gn-Pc n.d. 

82DB2983 48.6 15.3 .1 36.0 com4 com tr ap,zi chl ,sp,pr ,se Fo-Ln-Au 40 

82DB2993 46.5 15.7 .3 37.6 com4 com tr ap,zi chl,sp,ep,se Fo-Gn-Au-Ln 36 

7 82DB3023 51 .6 15.2 0 33.2 com4 com tr ap,zi chl,sp,ep Fo-Gn-Ln-Au 40 

8 82DB3053 51.9 22.1 5.2 20.8 com4 com min ap,zi chl ,pr ,sp Fo-Gn-Ln 39 

82DB3073 50.6 17.6 .5 31.4 com uncom min ap chl,sp,opq Fo-Gn-Ln-Pb 38 

TO 64AB236 abnt com tr 25 com com tr Ga,Ep,ap,zi chl,sp,mu,ep Fo-Gn-Au-Pb 40 

TO 64AB236 abnt com tr 30 com com tr Ep,ap,zi,al Ep,chl,sp Fo-Gn-Au-Pb n.d. 

TO 65AF275 abnt com min 25 com uncom tr ap,zi,ga ca,chl,sp Fo-Gn-Eg 37 

TO 65AF274 abnt com tr 40 com uncom min Ga,ap,zi chl ,sp Fo-Gn-Pb 40 

TO 65AF283 com abnt min 15 com tr Al,ap,zi chl ,sp Fo-Gn-Pb 32 

Average 49.8 17.2 1.2 31.8 

Standard 

deviation 2.3 2.9 2.2 6.6 

Number of 

samples 5 5 

Rock name rather than map number reported where no modal analysis was done. 

2 Border phase. 

3 Main phase. 

4 Most abundant mafic mineral. 

32 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
Table 8. Petrographic and major-element chemical data for the Lemon 

Creek Glacier pluton-Continued 

B. Major-element chemical data 

[Samples were analyzed in laboratories of the U.S. Geological 

Survey by x-ray fluorescence. FeO was determined by wet chemical 

methods. Results normalized to 100-percent volatile free; 

percentages may not add up exactly to 100.00 because oxide and 

norm values were rounded off from three to two decimal places. 

LOI, loss on ignition (H20 and C0 2); Norm, normative; Ci, color 

index; An, anorthite content of plagioclase; DI, differentiation 

index--sum of normative quartz, orthoclase, albite, nepheline, and 

leucite; ---, absent] 

Sample No.---80DB 

021 

Map No.-------10 

(fig. 1 5) 

Si02 

Al 2o3 

Fe 2o3 

FeO 

MgO 

CaO 

Na 2o 

K20 

Ti02 

P205 

MnO 

LOI 

Quartz 

Orthoclase 

Albite 

Anorthite 

Diopside 

Hypersthene 

Olivine 

Magnetite 

Ilmenite 

Apatite 

Norm CI 

Norm An 

DI 

57.14 

18.71 

1. 68 

5.37 

3.37 

7.32 

3. 73 

1. 32 

.97 

.30 

.11 

. 41 

8.15 

7.81 

31 .47 

30.39 

3.29 

13.85 

2.43 

1. 84 

.68 

21.4 

49.1 

47.5 

82DB 

303 

11 

82DB 

305 

8 

87733 87JS 

09 

12 12 

86DB 

049 

4 

86DB 

052 

13 

Whole-rock analyses (weight percent) 

51.12 57.25 

19.87 18.13 

1. 80 1. 70 

7.63 5.94 

4.90 3.47 

9.11 6. 90 

3.51 3.45 

1. 16 1. 66 

.36 1 .05 

. 40 . 34 

.15 .12 

.50 .61 

59.94 58.66 

14.55 17.90 

2. 70 1. 95 

4.58 4.60 

3.78 3.38 

7. 65 7. 59 

3.77 3.48 

1. 71 1. 23 

.87 .72 

.29 .34 

.14 . 14 

. 71 . 56 

CIPW norms (weight percent) 

6.85 

29.68 

35.05 

6.20 

8. 71 

9.28 

2. 61 

.69 

. 94 

27.5 

54.1 

36.5 

8. 81 

9.80 

29.20 

29.07 

2.45 

15.44 

2.47 

1. 98 

.78 

22.3 

49.9 

47.8 

11.91 

10.13 

31.93 

17.71 

14.89 

7.20 

11.95 

7.29 

29.44 

29.59 

4.75 

12.01 

3.91 2.83 

1. 66 1. 36 

. 67 . 80 

27.7 20.9 

35.7 50.1 

31.2 48.7 

57.16 56.58 

19.05 17.83 

3. 30 1. 55 

3.69 5.99 

1.95 3.45 

7.50 8.01 

4.30 3.45 

1. 84 1. 20 

. 72 1 .12 

. 29 . 59 

.21 .12 

1.49 .12 

7.19 

10.90 

36.40 

27.23 

6. 61 

4.86 

4.78 

1. 36 

.66 

17.6 

42.8 

54.5 

8.90 

7.07 

29.17 

29.96 

4.90 

14.27 

2.25 

2.12 

1. 36 

16.6 

45.7 

55.2 

Figures 3-23; Tables 1-11 33 
58° 

20' 

134°20' 

I I 

/ Lemon Creek 

GJacie_r pl~ton, 1 

0 2 

TAKU INLET 

'\1 

·' / 

\. .···:.-:-.: __ ;:·:. ~ . . 

I ' I 

3 4 5 KILOMETERS 

·::/·if.;;>::.<, Taku Cabin 

' ~ "pluton 

/ 

'i II 'l II 

' / == ,, :::: 

/ Gneiss 

/ ' / 

' / ' ' 

' / / 

12• \ 

\ 

' I ' ' / / 

/ / 

/ ' 

--/ ' / / -

Figure 17. Geologic sketch map of the Carlson Creek pluton, showing sample locations. Heavy line indicates fault. Contacts 

dashed where approximately located. 

34 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
GR 

QM 

MO 

Alkali feldspar Plagioclase feldspar 

Figure 18. Compositional modes of selected 

samples from the Carlson Creek pluton plotted on plutonic rock classification diagram of 

Streckeisen (1973). Average modal composition shown by dark triangle. GR, granite; GD, 

granodiorite; TO, tonalite; QM, quartz monzonite; QO, quartz monzodiorite; QD, quartz 

diorite; MO, monzonite; MD, monzodiorite; 

and Dl, diorite. 

Table 9. Petrographic and major-element chemical data for the Carlson Creek pluton 

Major rock types: 

Biotite-hornblende tonalite and quartz diorite 

Minor rock type: 

Hornblende-biotite granodiorite 

Location: 

East of Juneau and northwest and southeast of Taku Inlet 

Age: 

67 Ma (Gehrels and others, 1984) 

Description: 

Medium gray to brownish gray, homogeneous to locally layered; medium to coarse grained and locally fine 

grained; foliated, locally lineated, gneissic, and porophyroblastic to inequigranular. Hornblende more common 

than biotite. Composed of coarse-grained, anhedral, porphyroblastic and augen-shaped plagioclase; medium- to 

coarse-grained, anhedral to subhedral, elongated, tabular hornblende; fine- to medium-grained platy biotite; 

medium- to coarse-grained, anhedral granular and stretched quartz; and intergranular quartz and K-feldspar. 

Color index range 17-33, color index average 26 

Comments: 

Rock composed of two phases: a felsic-rich phase of granodiorite or tonalite and a felsic-poor phase of quartz 

diorite. Quartz diorite more common in lower, more deformed and metamorphosed part of pluton 

(Table continued on next page.) 

Figures 3-23; Tables 1-11 35 
Table 9. Petrographic and major-element chemical data for the Carlson Creek pluton-Continued 

A. Petrographic data 

[Results in percent. An, anorthite content of plagioclase; TO, tonalite; GD, granodiorite; n.d., not determined; 

See table 5 for other abbreviations] 

Map 

No. 1 

(fig. 

17) 

6 

7 

8 

9 

10 

11 

12 

13 

TO 

TO 

TO 

TO 

GD 

TO 

TO 

TO 

GD 

TO 

TO 

TO 

TO 

Sample 

No. 

Plagio- Quartz 

clase 

85DB086 54.7 

85EL113 50.2 

85SD116 54.0 

85SD118 58.5 

86DB053 59.2 

86DB054 67.8 

86DB055 64.3 

86SE005 50.3 

8708010 53.2 

87SK089 45.9 

87RK164 56.4 

87WN118 65.9 

88DB029A 55.7 

64AF118 abnt 

64AF1 21 a bnt 

85SD117 abnt 

65Bd017 abnt 

65Bd019 abnt 

65Bd015 abnt 

65Bd021 abnt 

64Bd230 abnt 

64Bd232 com 

64Bd241 abnt 

65Bd399 abnt 

68Bd373 abnt 

68Bd377 abnt 

Average 56.6 

Standard 

deviation 6.4 

Number of 

samples 13 

35.4 

25.3 

21.4 

8.1 

4.7 

14.8 

13.5 

27.5 

15.1 

20.9 

10.1 

24.0 

24.4 

com 

com 

com 

com 

com 

com 

com 

com 

com 

com 

com 

com 

com 

18.9 

8.7 

13 

K-feld- Mafic 

spar minerals 

8.8 

5.7 

1.3 

0 

0 

0 

.3 

.2 

.1 

3.2 

1.1 

.2 

13.9 

tr 

min 

tr 

tr 

uncom 

min 

min 

min 

com 

min 

tr 

min 

min 

2.7 

4. 3 

13 

18.8 

23.3 

33.4 

36.1 

17.4 

21.9 

22.0 

31.6 

30. 1 

32.4 

10.0 

9.6 

20 

16 

25 

25 

20 

22 

25 

20 

25 

30 

30 

25 

32 

23.8 

8.9 

12 

Hornblende 

tr 

uncom 

com 

com 

com 

uncom 

com 

com 

com 

com 

com 

uncom 

com 

com 

com 

com 

com 

com 

com 

com 

uncom 

com 

com 

com 

com 

com 

Biotite Opaques Sphene 

min tr 

com tr tr 

uncom tr tr 

com tr 

uncom min 

uncom tr 

uncom tr 

uncom tr tr 

com min tr 

com tr 

com tr 

uncom tr 

min min tr 

uncom tr 

uncom tr min 

uncom tr 

uncom tr 

uncom tr 

uncom tr 

uncom tr tr 

com tr tr 

uncom tr 

com tr 

com tr tr 

com tr 

com tr 

Rock name rather than map number reported where no modal analysis was done. 

2 Low mafic count (not counted in average). 

Accessory 

minerals 

Ga,ap,zi 

ap,zi,al 

Ap, zi 

Ap,zi,al 

Ap,zi 

Ga ,ap,zi 

Al,ap,zi 

ap,zi 

ap,al 

ap,zi 

ap, zi 

ap,zi 

ap, zi 

ap,zi,al 

ap, zi 

ap,zi 

ap,zi 

ap,zi 

ap, zi 

ap,zi 

ap,zi ,al 

Secondary 

minerals 

chl,mu,sp 

chl ,ep ,sp ,se 

chl,ep,sp,se 

chl ,sp,pr ,ep 

chl ,sp, pr 

chl ,sp,se 

chl,sp,pr,ep 

chl ,sp,ca ,ep 

chl ,sp ,ep ,se 

chl ,sp,ep,se 

chl,ep,sp,pr 

chl ,sp,ep 

chl,sp,ca 

chl ,sp,ep,se 

chl,sp,se 

chl,ep,se,sp 

ep,se,chl,sp 

chl ,sp,se,opq 

chl,sp,se 

chl ,ep,sp,opq 

se,sp,opq 

Al,ap,zi Ep,chl,sp,se 

Ap,Al,zi,px sp,se,pr 

ap,zi chl,ep,sp 

ap,al chl,opq,sp 

ap,zi chl,ep,ca,se 

36 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 

not present. 

Main 

texture 

Fo-Gn-La 

Fo-Gn-Pb 

Fo-Iq 

Fo-Ln-Au 

Fo-Gn-Pb 

Fo-Gn-Pb 

Fo-Gn-Pb 

Fo-Al-Eg 

Fo-Gn-Au 

Fo-Au-I q 

Fo-Iq 

Fo-Iq 

Fo-Gn 

Fo-Gn-Pb 

Fo-Gn-Au-Pb 

Fo-Gn-Iq 

Fo-Gn-Iq 

Fo-Gn-Pb 

Fo-Gn-Pb 

Fo-Al-Gr 

Fo-Gn-Au-La 

Fo-Gn-La-Au 

Fo-Pb-Au 

Fo-Pb-Iq 

Fo-Gn-Eg 

Fo-Iq 

An 

n.d. 

31 

38 

39 

37 

34 

38 

36 

40 

34 

40 

n.d. 

n.d. 

n.d. 

40 

n.d. 

40 

n.d. 

39 

36 

37 

39 

36 

39 

33 

45 
Table 9. Petrographic and major-element chemical data for the Carlson Creek plutonContinued 

B. Major-element chemical data 

[Samples were analyzed in laboratories of the U.S. Geological Survey by x-ray 

fluorescence. FeO was determined by wet chemical methods. Results normalized to 

100-percent volatile free; percentages may not add up exactly to 100.00 because 

oxide and norm values were rounded off from three to two decimal places. LOI, loss 

on ignition (H 2o and co 2); Norm, normative; CI, color index; An, anorthite content 

of plagioclase; DI, differentiation index--sum of normative quartz, orthoclase, 

albite, nepheline, and leucite] 

Sample No.-- 85SD 80SK 85EL 8215 87DB 87SK 87RK 86DB 86DB 86DB 

11 6 126 11 3 010 089 164 053 055 054 

Map No.----- 3 1 4 2 9 10 11 5 7 6 

(fig. 17) 

Whole-rock analyses (weight percent) 

Si02 62.18 59.03 65.74 57.06 57.43 61.94 56.64 58.90 61.73 59.17 

Al 2o3 17.29 17.52 1 6. 41 18.78 1 8. 57 17.25 18.54 18.72 17.87 18.17 

Fe2o3 3.39 1.1 3 1. 23 2.52 2. 01 . 98 1. 64 . 31 • 31 .56 

FeO 2.09 5.75 3. 10 4.40 4.67 4.66 5.39 5.53 4.95 5.55 

MgO 2.65 3.34 2.02 3. 52 3.48 2.76 3.69 2.83 2.34 3.03 

CaO 6.27 6.47 4.82 7.50 7.69 6. 31 7.68 7. 54 6.50 7.55 

Na 2o 3.66 3.37 3.56 3.53 3. 53 3.53 3.58 3.85 3.86 3.64 

K20 1. 50 1. 99 2.28 1. 36 1. 33 1. 58 1. 43 1. 00 1. 34 1.10 

Ti0 2 .62 1. 01 . 60 .93 .84 .65 .98 .83 . 71 .74 

P205 .26 .28 .17 .27 .33 .23 .30 .39 . 32 .36 

MnO .1 0 .11 .08 .11 .12 .11 .13 .11 .09 .12 

LOI .74 .34 .56 1. 01 . 71 .59 .54 .37 .64 .25 

CIPW norms (weight percent) 

Quartz 1 9. 09 1 o. 82 21.89 9. 51 9.55 15.93 7.24 10.30 1 4. 66 11 .22 

Orthoclase 8.84 11.73 1 3. 47 8.04 7.86 9.36 8.46 5.92 7.92 6.56 

Albite 30.97 28.53 30.08 29.90 29.88 29.87 30.27 32.54 32.64 30.76 

Anorthite 26.33 26.80 22.09 31. 38 30.89 26.54 30.31 30.86 27.48 29.99 

Diopside 2. 39 2.85 .58 3.29 4.20 2.67 4.77 3.36 2.26 4.24 

Hypersthene 5.70 15.05 8.58 11.83 12.36 12.45 1 4. 02 1 4.11 12.53 1 4. 18 

Magnetite 4. 91 1. 64 1. 78 3.65 2.91 1. 42 2.38 .46 .44 .81 

Ilmenite 1. 17 1. 92 1. 14 1. 77 1. 60 1. 23 1. 86 1. 58 1. 35 1. 40 

Apatite . 61 • 66 .40 . 64 .75 .54 .70 .89 .73 .84 

Norm CI 14.2 21.5 1 2.1 20.6 21.1 17.8 23.0 1 9. 5 16.6 20.6 

Norm An 45.9 48.4 42.3 51.2 50.8 47. 1 50.0 48.7 45.7 49.4 

DI 58.9 51.1 65.5 47.5 47.3 55.2 45.0 48.8 55.2 48.5 

Figures 3-23; Tables 1-11 37 
38 

134°20' 

' / ' / 

/ ' / ' 

' Gneiss / ' / ' / ' / 

' / ' / ' 

r" - Annex Lakes \ ~--;-, - I \...__ ', / ' 

/ ' / ' 

Lakes pluton, ·c sketch map of the approximate Annex I Y located. 9 Figure 1 . Geolog1 h d where It Contacts das e indicates tau . 

showing sample locations. Heavy line 

Petrographic a nd Chern• ·cal Data fort h e Large MeSOZOIC . d an Cenozoic . Plutonic S•l . 1 s, Alaska 
GR 

• 

Alkali feldspar 

QM 

MO 

Plagioclase feldspar 

Figure 20. Compositional modes of selected 

samples from the Annex Lakes pluton plotted 

on plutonic rock classification diagram of 

Streckeisen (1973). Average modal composition shown by dark triangle. GR, granite; GO, 

granodiorite; TO, tonalite; QM, quartz monzonite; QO, quartz monzodiorite; QD, quartz 

diorite; MO, monzonite; MD, monzodiorite; 

and 01, diorite. 

Table 10. Petrographic and major-element chemical data for the Annex Lakes pluton 

Major rock types: 

Sphene-bearing hornblende-biotite granodiorite and sphene-bearing biotite-hornblende granodiorite 

Minor rock types: 

Biotite granite and granodiorite, sphene- and hornblende-bearing biotite tonalite, and hornblende-biotite quartz 

monzodiorite 

Location: 

East of Juneau and west of Taku Inlet 

Age: 

60 Ma ( Gehrels and others, 1984) 

Description: 

Light to medium gray, heterogeneous, fine to coarse grained, strongly to weakly foliated and locally lineated, 

gneissic to inequigranular and locally porphyroblastic or porphyritic. Contains mafic-rich segregations to weak 

layering. Biotite generally more abundant than hornblende. Rock typically contains coarse-grained to phenocrystic, 

anhedral K-feldspar; medium- to coarse-grained, subhedral plagioclase; fine- to medium-grained, platy biotite; 

medium-grained, subhedral, tabular or elongated hornblende; medium- to fine-grained, granular to intergranular 

quartz; and fine-grained interstitial K-feldspar. Sphene and allanite are conspicuous and locally common. Color 

index range 5-27, color index average 13 

Comments: 

Core zone (Flat Point pluton) is composed of weakly foliated, homogeneous coarse-grained biotite granodiorite 

and medium- to coarse-grained hornblende-biotite tonalite. Pluton is very heterogeneous in lithology and texture 

and might be a composite sill body of three to four individual sills 

(Table continued on next page.) 

Figures 3-23; Tables 1-11 39 
Table 10. Petrographic and major-element chemical data for the Annex Lakes pluton-Continued 

A. Petrographic data 

[Results in percent. An, anorthite content of plagioclase; GR, granite; GD, granodiorite; QM, quartz monzonite; TO, tonalite; n.d., not 

determined; ---, not present. See table 5 for other abbreviations] 

Map Sample Plagio- Quartz K-feld- Mafic Horn- Biotite Opaques Sphene 

No. 1 No. clase spar minerals blende 

(fig. 

19) 

86AF095 42.5 19.6 222.6 15.3 

86AF096 56.7 34.7 3.9 4. 7 

86AF099 44.8 26.3 20.1 8.8 

80DB01 6 61.1 11.5 26.8 

86SK374 60.7 20.9 11.6 

80SK122 53.7 16.1 15.2 15.0 

87AF096 41.1 33.0 21.3 4. 6 

83 87DB011 60. 0 25. 5 2.8 11.8 

93 82GS112 55.2 27.5 • 7 16.6 

1 0 86SK363 54.4 17.8 

11 88KS141 29.3 26.1 41.4 

12 88SK142 55.8 18.4 218.1 

3. 2 

7. 8 

13 88SK143 51.8 24.4 18.1 5. 6 

14 88SK144 53.4 22.5 218.3 5. 8 

15 88SK145 53.9 30.3 1.7 14.0 

16 88SK146 47.2 7.9 218.0 26.8 

17 8808630 59.4 13.1 7.6 19.8 

18 8808031 45.9 23.3 13.9 17.0 

19 8808032 37.3 22.5 14.1 26.2 

20 8808033 253.4 22.2 210.6 14.0 

213 8808034 47.9 26.7 19.1 6. 3 

22 8808035 55.5 30.3 1.1 13.2 

GR 8308080 abnt com com 15 

GO 85El111 abnt com uncom 20 

QM 8308081 com uncom com 

TO 

TO 

GO 

GO 

GR 

GR 

GO 

GR 

GR 

GO 

GR 

GR 

64Fd068 abnt com 

65Fd070 abnt com 

65Fd073 abnt com 

65Bd106 abnt com 

65Bd 1 00 com com 

65Fd077 com com 

65Fd091 abnt com 

65Bd411 com com 

65Fd080 com com 

64Bd050 a bnt com 

64Bd051 com com 

64Bd052 com com 

Average 50.4 21.6 

Standard 

deviation 8. 4 

Number of 

samples 19 

7. 8 

19 

min 17 

min 35 

min 21 

uncom 26 

com 15 

com 

uncom 22 

com 15 

com 26 

uncom 31 

com 

com 11 

1 4. 4 13.6 

9. 8 7. 6 

19 19 

min uncom tr min-eu 

min tr 

uncom min min tr-an 

com com tr min-sbh 

uncom min tr min-an 

uncom uncom tr min-eu 

min tr tr-an 

min uncom min min-sbh 

uncom uncom tr tr-sbh 

uncom com min tr-sbh 

tr min min 

uncom tr min min-sbh 

min min tr tr-sbh 

min min min min-sbh 

min com tr tr-sbh 

com min tr min-sbh 

min com min tr-an 

uncom com min min-sbh 

com uncom tr tr-s bh 

tr com tr min-eu 

tr uncom tr tr-an 

min com min min-sbh 

min uncom min tr-sbh 

com uncom min min-eu 

uncom min tr-sbh 

min com tr min-sbh 

com uncom min min-an 

com uncom min tr-an 

com com tr min-an 

uncom min min min-eu 

min min min tr-an 

com com min min-an 

com min tr-an 

min com min min-an 

com com tr min-sbh 

tr uncom min tr-an 

com min tr-sbh 

1 Rock name rather than map number reported where no modal analysis was done. 2 Phenocrysti c (greater than 1 em). 

3 Flat point pluton (core of Annex Lakes pluton); not counted in average. 

Accessory 

minerals 

Ap ,zi ,al 

ap,zi 

ap,zi 

Ap ,zi 

Ap, zi ,al 

ap,zi,al 

ap ,al, zi 

ap,zi ,al 

ap,zi 

Ap,zi 

A1 ,ap,zi 

Ap ,al,zi 

ap,zi ,al 

ap,zi,al 

ap,zi 

ap,al,zi 

ap,zi 

ap,zi,al 

ap,zi,al 

ap,zi,al 

Al,ap,zi 

ap,al 

Al,Ap,zi 

Ap,zi ,al 

Al,ap,zi 

Ap 

Ap ,zi 

ap,zi 

ap,zi 

ap,zi 

Al,ap, zi 

ap,al,zi 

ap ,al, zi 

Al,ap,zi 

ap ,zi 

Al,ap,zi 

ap,zi 

Secondary 

minerals 

chl ,sp ,se 

chl,mu,sp 

chl ,sp ,se 

chl,ep,pr,se 

chl,sp,pr,se 

chl,ep,sp,se 

chl,mu,ep ,sp 

chl,ep,sp,se 

chl ,ep 

chl ,se ,ca 

chl,mu,ep 

chl,sp ,se 

chl ,sp ,se 

chl,sp 

ep ,chl ,sp 

chl ,sp 

chl ,sp 

chl,sp ,se 

chl,sp,ep,pr 

chl,mu,pr 

chl ,sp ,se 

chl,sp,ep 

Chl,mu,sp 

chl ,ep ,sp 

chl,sp,mu 

chl,sp,se 

chl,sp,pr 

chl ,sp 

chl,sp ,se ,pr 

chl,sp,ep,se 

chl ,sp ,se 

chl,sp 

chl,mu 

chl,sp,opq,se 

chl ,sp ,se ,ep 

chl ,mu,sp 

chl ,mu ,sp ,ep 

40 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 

Main 

texture 

Fo-Hy-Eg 

Hy-Eg 

Fo-Hy-Iq 

Fo-Eg-Eq 

Fo-Pb-Al 

Fo-Ln-Iq 

Fo-La-Iq 

Iq-Eq 

Eg 

Fo-Ln-Pb 

Fo-Al-Eg 

Iq-Pp 

Fo-Iq-Al 

Fo-Gn-Pb 

Fo-Al-Gn 

Fo-Pp-Al 

Fo-Al-Iq 

Fo-Iq-Gn 

Fo-Gn-Al 

Fo-Pp-Iq 

Fo-Pp-Iq 

Fo-Iq-Pp 

Fo-Gn-Pb 

Fo-Gn-Iq 

Fo-Iq-Al 

Fo-Gn-Iq 

Fo-Gn-Iq 

Fo-Gn-Pb 

Fo-Gn-Ln 

Pb-Gr 

Pp-Al-Gr 

Fo-Gn-Iq 

Fo-Al-Iq 

Fo-Gn-Al 

Fo-Gn-Ln 

Fo-Gn-I q 

Iq-Al 

An 

n.d. 

n.d. 

37 

38 

34 

33 

34 

35 

n.d. 

n.d. 

n.d. 

32 

n.d. 

n.d. 

n.d. 

n.d. 

31 

33 

n.d. 

27 

n.d. 

n.d. 

24 

36 

28 

43 

45 

30 

38 

24 

29 

33 

30 

26 

38 

28 

29 
Table 10. Petrographic and major-element chemical data for the Annex Lakes pluton-Continued 

B. Major-element chemical data 

[Samples were analyzed in laboratories of the U.S. Geological Survey by x-ray fluorescence. FeO was 

determined by wet chemical methods. Results normalized to 100-percent volatile free; percentages may 

not add up exactly to 100.00 because oxide and norm values were rounded off from three to two decimal 

places. LOI, loss on ignition (H2o and co2); Norm, normative; CI, color index; An, anorthite content 

of plagioclase; DI, differentiation index--sum of normative quartz, orthoclase, albite, nepheline, and 

leucite; ---, absent] 

Sample No.--80SK 

122 

Map No.----- 6 

(fig. 19) 

80DB 82GS 86AF 86AF1 86AF 

016 112 095 096 099 

2 

86SK 

363 

10 

86SK 

374 

5 

(JS10) JS41 87DB 87JS 

87734 011 10 

23 8 8 23 

87AF 

096 

7 

Whole-rock analyses (weight percent) 

Si02 

Al 2o3 

Fe2o3 

FeO 

MgO 

CaO 

Na2o 

K20 

Ti0 2 

P205 

MnO 

LOI 

65.78 

17.13 

1. 30 

2.05 

1.46 

4.75 

4.12 

2.79 

.40 

.18 

.06 

.45 

60.01 

17.87 

2.08 

4.18 

2.80 

6.12 

3.75 

1. 92 

.89 

.24 

.12 

.54 

64.46 

17.03 

1. 81 

2.75 

1. 54 

5.06 

3.75 

1. 68 

.60 

.25 

.07 

.37 

61.85 73.14 

18.41 16.24 

1. 79 .05 

2.26 .47 

1. 53 . 35 

4.92 1.83 

4.88 6.46 

3. 09 1. 26 

.66 .09 

. 51 . 06 

. 09 . 04 

.25 .25 

67.91 

15.97 

1. 41 

2. 01 

1. 21 

3. 81 

3.64 

3. 21 

. 51 

.24 

.08 

60.54 

17.34 

2.33 

3.23 

2.45 

4.85 

3.94 

3.93 

.81 

.48 

.11 

. 38 4.13 

CIPW norms (weight percent) 

65.65 

16.82 

1. 55 

2.53 

1. 51 

5.06 

3.73 

2. 41 

.38 

.26 

.09 

.13 

65.34 58.95 

18.34 18.47 

1.40 2.53 

2.02 4.29 

.88 3.03 

5.49 6.60 

4.56 3.50 

1. 37 1. 47 

. 35 .81 

. 12 . 24 

.13 .1 0 

.39 . 91 

67.13 66.65 

16.78 17.47 

1.62 1.76 

2.17 1. 57 

1. 23 . 87 

4.95 5.39 

3.95 4.33 

1. 38 1. 30 

. 50 . 35 

.23 .17 

.05 .13 

.53 .35 

69.03 

17.41 

1.27 

1. 22 

.75 

4.52 

4.42 

.99 

.26 

.08 

.07 

.54 

Quartz 

Corundum 

18.86 12.66 23.53 9.85 26.15 24.33 9.24 21.36 20.02 13.03 26.20 23.88 28.60 

Orthoclase 16.47 

Albite 34.82 

Anorthite 20.03 

Diopside 1.92 

Hypersthene 4.85 

Magnetite 1.88 

Ilmenite .75 

Apatite .42 

Norm CI 

Norm An 

DI 

9.4 

36.5 

70.15 

11.34 

31.70 

.43 

9.94 

31.75 

26.28 23.49 

2.05 

10.69 6.54 

3.02 2.62 

1. 70 1.14 

. 56 . 57 

17.5 

45.3 

55.71 

10.3 

42.5 

65.22 

18.27 

41.32 

19.20 

1. 55 

4.80 

2.60 

1. 26 

1.18 

10.2 

31.7 

69.44 

1. 08 

7.45 

54.63 

8.66 

1. 63 

.07 

.17 

. 14 

1.9 

13.7 

88.24 

1Altered rock, not counted in average. 

. 16 

18.99 23.20 

30.78 33.31 

17.32 18.06 

2.34 

4.87 7.84 

2.04 3.38 

. 96 1. 54 

.56 1.11 

7.9 15.1 

36.0 35.2 

74.10 65.75 

1 4. 22 

31.52 

22.05 

1. 20 

6.07 

2.25 

.73 

. 61 

10.2 

41.2 

67.10 

.34 

8.11 8.71 8.13 7.70 

38.58 29.64 33.45 36.66 

25.52 30.33 23.06 24.38 

.78 .68 1.02 

4.02 11.86 5.00 2.75 

2.03 3.67 2.35 2.55 

.67 1.53 .94 .67 

.28 

7.5 

39.8 

66.71 

.56 .54 .40 

17.7 8.3 7.0 

50.6 40.8 39.9 

51.37 67.77 68.24 

1. 05 

5.83 

37.38 

21 .89 

2.74 

1. 84 

.50 

. 19 

5.1 

36.9 

71 .80 

Figures 3-23; Tables 1-11 41 
TAKU 

. ·~ 

,_:,· / ' / 

/ ' / ' 

' / ' / 

/ ' / ' 

' / ' / 

/ ' / ' 

' / ' / 

58°15' 

/ ' / ' 

' / ' / 

/ ' / ' 

' / ' / 

Taku Cabin pluton 

/ 

' / 

/ ' 

' / 

/ ' 

' / 

/ ' I 

Gneiss 

/ ' 

' / 

0 

9• 

5e 

/ 

' / 

/ ' / 

' / ' / ' / 

' / ' / ' / 

' / ' 

1• 

2• 

4• 

6• 

3• 

/ 

' / 

/ ' / 

' / ' / ' ' 

2 3 Kl LOM ETE RS 

Figure 21. Geologic sketch map of the Taku Cabin pluton, showing sample locations. Contacts dashed 

where approximately located. 

42 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
GR 

QM 

MO 

Alkali feldspar Plagioclase feldspar 

Figure 22. Compositional modes of samples 

from the Taku Cabin pluton plotted on plutonic rock classification diagram of Streckeisen 

(1973). Open square is mode on sample from 

felsic sill layer in pluton. Average modal composition shown by dark triangle. GR, granite; 

GD, granodiorite; TO, tonalite; QM, quartz 

monzonite; QO, quartz monzodiorite; QD, 

quartz diorite; MO, monzonite; MD, monzodiorite; and Dl, diorite. 

Table 11. Petrographic and major-element chemical data for the Taku Cabin pluton 

Major rock type: 

Sphene-biotite-hornblende tonalite 

Minor rock type: 

Sphene- and allanite-bearing hornblende-biotite granodiorite 

Location: 

Taku Inlet, south of Turner Lake and north of Lake Dorothy 

Age: 

55 to 60 Ma 

Description: 

Light to medium gray, homogeneous, medium to coarse grained, and foliated. Typically hypidiomorphic 

equigranular but ranges from seriate to inequigranular. Contains medium- to coarse-grained subhedral plagioclase; anhedral quartz; interstitial K-feldspar and quartz; and coarse- to medium-grained, tabular, euhedral 

hornblende and platy biotite. Hornblende more common than biotite in tonalite, and biotite more common in 

granodiorite. Well jointed. Sphene and magnetite conspicuous. Locally, hornblende phenocrystic ( > 1 em). Color 

index range 15-23, color index average 19 

Comments: 

Granodiorite forms sill layer in tonalite. Some quartz diorite in lower border-phase rocks. Not as deformed or 

metamorphosed as Mount Juneau, Carlson Creek, or Lemon Creek Glacier plutons. Body is very similar to 

Mendenhall Glacier pluton 

(Table continued on next page.) 

Figures 3-23; Tables 1-11 43 
Table 11. Petrographic and major-element chemical data for the Taku Cabin pluton-Continued 

A. Petrographic data 

[Results in percent. An, anorthite content of plagioclase; GD, granodiorite; QD' quartz diorite. See table 5 for other abbreviations] 

--------

Map 

No. 1 

(fig. 

21) 

2 

53 

7 

GD 

QD 

GD 

GD 

QD 

Sample Plagio- Quartz K-feld- Mafic Horn- Biotite Opaques Sphene 

No. clase spar minerals blende 

85DB110 56.5 22.5 4.4 16.6 com uncom min min-sbh 

85DB111 57.8 22.1 3.6 16.5 com uncom min uncom-sbh 

85DB112 54.5 23.8 2.3 19.4 com uncom min uncom-sbh 

85SD068 56.1 24.8 3.7 15.4 uncom2 uncom min min-sbh 

85SD067 40.6 29.0 1 9. 4 11.0 tr uncom min min;..sbh 

85El065 61 .5 20.9 .8 16.8 uncom2 uncom min min-sbh 

85SD108 58.4 17.4 2.1 22.1 com uncom min min-eu 

86RK085 58.1 21.1 .3 20.5 com uncom min min-eu 

85El069 51.2 20.9 4.7 23.2 com uncom min min-sbh 

85El071 com com com 10 min uncom min tr-an 

85WN087 abnt uncom min 25 com min min min-sbh 

65F'd053 abnt com com 15 min uncom min tr-an 

65F'd054 abnt uncom min 15 uncom uncom min tr-an 

85WN086 abnt com uncom 30 com uncom min min-sbh 

Average 56.8 21.7 2.7 18.8 

Standard 

rjeviation 3.0 2.2 1.6 2.g 

Number of 

samples 8 8 8 8 

Rock name rather than map number reported where no modal analysis was done. 

2 Most abundant mafic mineral. 

F'elsic sill layer in tonalite--not included with main-phase average. 

Accessory Secondary 

minerals minerals 

Ap,zi chl , s p , pr , chl 

ap,zi chl,sp,ep,pr 

ap,zi chl ,sp ,ep, pr 

ap,zi chl ,sp,opq 

al,ap,zi chl,ep,mu,sp 

ap,zi chl ,sp,ep,pr 

ap,zi chl,sp,ep,pr 

ap,zi chl ,sp ,ep ,pr 

ap ,zi chl,sp,ep 

al ,ap,zi chl ,sp,clz,ep 

ap ,zi chl,ap,sp,pr 

Al,ap,zi Ep ,chl ,sp,se 

Al,ap,zi Ep,chl ,sp,se 

ap,zi chl ,sp,se 

44 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 

Main An 

texture 

Fo-Ln,Eg 38 

Fo-Hy-Eg 39 

Fo-Se-Eg 40 

Fo-Hy 39 

Fo-Hy-Eg 32 

Fo-Hy-Eg 34 

Fo-Hy-Eg 39 

Fo-Hy-Eg 40 

Fo-Hy-Eg 41 

Fo-Al 31 

Fo-Gn-Hy 36 

Al-Iq-Pp 31 

Al 34 

Fo-Hy-Eg 40 
A 

8 

Figure 23. Stained slabs from the Juneau sills, showing 

typical textures of each pluton. Plagioclase is medium dark 

gray, K-feldspar is grayish white, and quartz is light gray. A, 

Gneissic hornblende-biotite tonalite from the Mount Juneau 

pluton; 8, weakly foliated biotite-hornblende tonalite from the 

Mendenhall Glacier pluton; C, foliated and weakly banded 

biotite-hornblende tonalite from the Lemon Creek Glacier 

c 

D 

pluton; D, strongly foliated biotite-hornblende tonalite from 

the Carlson Creek pluton; E, foliated equigranular biotitehornblende tonalite from the Taku Cabin pluton; F, weakly 

foliated porphyritic biotite granodiorite from the Annex Lakes 

pluton (phenocrysts are K-feldspar); and G, gneissic 

hornblende-biotite granodiorite from the Annex Lakes pluton. 

46 Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills, Alaska 
Table 11. Petrographic and major-element chemical 

data for the Taku Cabin pluton-Continued 

B. Major-element chemical data 

[Samples were analyzed in laboratories of the 

U.S. Geological Survey by x-ray fluorescence. 

FeO was determined by wet chemical methods. 

Results normalized to 100-percent volatile free; 

percentages may not add up exactly to 100.00 

because oxide and norm values were rounded off 

from three to two decimal places. LOI, loss in 

ignition (H2o and C0 2 ); Norm, normative; CI, 

color index; An, anorthote content of 

plagiocl ase; DI, differentiation index--sum of 

normative quartz, orthoclase, albite, nepheline, 

and leucite] 

Sample No.-------

Map No.------------

(fig. 21) 

85DB 

110 

85DB 

112 

3 

Whole-rock analyses (weight percent) 

Si02 

Al 2o3 

Fe 2o3 

FeO 

MgO 

CaO 

Na 2o 

K20 

Ti0 2 

P205 

MnO 

LOI 

61.56 

16.97 

2.66 

3.64 

2.78 

6.22 

3.38 

1. 76 

.68 

.22 

. 13 

.52 

CIPW norms (weight percent) 

Quartz 

Diopside 

Orthoclase 

Albite 

Anorthite 

Hypersthene 

Magnetite 

Ilmenite 

Apatite 

Norm CI 

Norm An 

DI 

17.43 

2.81 

10.39 

28.62 

25.92 

9.17 

3.86 

1. 29 

.52 

17.1 

47.5 

56.4 

61.68 

16.92 

2. 48 

3.89 

2.68 

6.30 

3.34 

1. 67 

.68 

. 23 

.12 

. 51 

17.85 

2.87 

9.88 

28.28 

26.21 

9.48 

3.60 

1. 29 

. 54 

17.2 

48.1 

56.0 

Figures 3-23; Tables 1-11 45 
E G 

F 

Figure 23.-Continued 

Figures 3-23; Tables 1-11 47 

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