Mantle Origin and Flow Sorting of 

Megacryst-Xenolith Inclusions in 

Mafic Dikes of Black Canyon, 

Arizona

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Mantle Origin and Flow Sorting of 

Megacryst-Xenolith Inclusions in 

Mafic Dikes of Black Canyon, 

Arizona

By Jane E. Nielson and John K. Nakata

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1541

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Robert M. Hirsch, Acting Director

For sale by

U.S. Geological Survey, Map Distribution

Box 25286, MS 306, Federal Center

Denver, CO 80225

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

not imply endorsement by the U.S. Government.

Text and illustrations edited by James W. Hendley II

Library of Congress Cataloging-in-Publication Data

Nielson, Jane E.

Mantle origin and flow sorting of megacryst-xenolith inclusions in mafic dikes of Black Canyon, Arizona / by Jane E. Nielson 

and John K. Nakata.

p. cm.—(U.S. Geological Survey professional paper ; 1541)

Includes bibliographical references.

Supt. of Docs, no.: 19.16:1541

1. Basalt—Inclusions—Black Canyon (Ariz. and Nev.) 2. Geology, Stratigraphic—Miocene. 3. Geology, Stratigraphic— 

Pliocene. 4. Geology—Arizona. I. Nakata, John K. II. Title. III. Series. 

QE462.B3N54 1994 

552'.26'0979159—dc20 93-23011 cn>

Cover—Segment of north-trending dike array in Black Canyon, Arizona. Tabular dike segment crosses fanglomerate 

ridge. At north end (left), dike incorporated a mass of the host fanglomerate and developed a bulbous swelh'ng. Wilson 

Ridge in background.
CONTENTS

Abstract.........................................................^ 1

Introduction................................................................................................................. 1

Acknowledgments....................................................................................................... 3

Geologic relations in Black Canyon........................................................................... 3

Extrusive and intrusive megacryst-bearing rocks....................................................... 5

Vent area............................................................................................................. 5

Tuff breccia deposits................................................................................ 5

Intrusions.................................................................................................. 5

Magnetic expression of the vent area...................................................... 6

Observations on the dike arrays.......................................................................... 6

Geologic relations and structures............................................................. 6

Internal features........................................................................................ 9

Structure-parallel joints.................................................................. 11

Cooling joints................................................................................. 13

Inclusion suite................................................................................. 13

Inclusion orientation and foliation................................................. 13

Inclusion distribution patterns........................................................ 14

Relation of inclusions and bulbous swellings................................ 15

Composition of dikes and inclusions.......................................................................... 16

Petrography and composition of dikes ............................................................... 16

Compositions of mafic inclusions ...................................................................... 18

Olivine...................................................................................................... 19

Pyroxene................................................................................................... 19

Amphibole................................................................................................ 23

Other minerals.......................................................................................... 25

Discussion.................................................................................................................... 25

Formation of the Black Canyon vent area........................................................... 25

Structures and intrusive process of the dike arrays............................................. 26

Origin of the mafic-ultramafic inclusion suite and host magma.......................... 27

Origin of zoning and inclusion distribution patterns .......................................... 28

Zoning...................................................................................................... 28

Inclusion concentrations and size sorting................................................ 28

Summary...................................................................................................................... 30

References cited.......................................................................................................... 30

FIGURES

1. Map showing outcrops of dikes in Black Canyon.................................................................................................... 2

2. Maps of vent area ........................................................... 2

3. Photograph showing bulbous dike in fanglomerate at north end of vent area......................................................... 5

4. Photograph showing longitudinal section and flow joints parallel to dike tip, location 11..................................... 8

5. Diagram showing idealized dike............................................................................................................................... 8

6. Photographs showing features of bulbous swellings................................................................................................ 9

7. Photographs showing fanglomerate incorporation by Black Canyon dikes............................................................. 10

8. Photograph showing dike with irregular distribution of massive and fissile joints................................................. 11

9. Diagrammatic representation of dike exposures (X, Y, Z) at location 13, U.S. Highway 93 ................................. 11

10. Photograph showing flow banding in marginal zone of dike ................................................................................ 12

11. Photographs showing distance and close up views of dike segment at location 13 ............................................... 12

m
IV CONTENTS

12. Photographs showing static cooling joints................................................................................................................ 13

13. Inclusion orientation, distribution, and abundance in dike at location 13................................................................ 15

14. Photograph showing fanglomerate in dike matrix of the contact zone.................................................................... 16

15. Quadrilateral compositions of pyroxene minerals..................................................................................................... 19

16. Amphibole compositional variations......................................................................................................................... 24

17. Amphibole (kaersutite) compositional variations in dike at location 13 ............................................................... 25

	TABLES

1. Characteristics of Black Canyon dikes...................................................................................................................... 4

2. Features of zoned dikes ............................................................................................................................................. 7

3. Compositions of dike matrix ..................................................................................................................................... 17

4. Compositions of clinopyroxene................................................................................................................................. 33

5. Compositions of orthopyroxene................................................................................................................................. 36

6. Compositions of amphibole (kaersutite).................................................................................................................... 37

7. Compositions of amphibole (pargasite) in xenoliths of Black Canyon dikes ........................................................ 20

8. Published compositions of Black Canyon kaersutite megacrysts ........................................................................... 22

9. Compositions of phlogopite and olivine.................................................................................................................... 23
Mantle Origin and Flow Sorting of Megacryst-Xenolith 

Inclusions in Mafic Dikes of Black Canyon, Arizona

By Jane E. Nielson and John K. Nakata

ABSTRACT

Three arrays of inclusion-bearing alkali basalt dikes, 1 

to 1.5 km in length, crop out in Miocene and Pliocene 

fanglomerate in Black Canyon, near the Colorado River, 

northwest Arizona. Erroneously called camptonite dikes, 

the best known exposures are in a series of roadcuts about 

16 km south of Hoover Dam. The origin of axial concentrations of inclusions in these dikes has long been debated. The 

north-trending dike arrays consist of at least 16 short segments, which are 61 to 366 m in length. Five of these 

segments pinch out at the north or south end, or both; where 

the tips of dike segments overlap, they may be deflected in 

opposite directions. These stress-related deflections show 

that the segments of each array were emplaced concurrently.

A vent area of related tuff breccia and multiple intrusions crops out at the south end of the dike arrays. The 

dikes, related tuff breccia, and a possible small lava flow all 

contain inclusions. Although the most distinctive inclusions 

are mafic to ultramafic mineral fragments (megacrysts) and 

xenoliths, the largest and most common inclusions are 

silicic igneous and metamorphic rocks from disaggregated 

masses of fanglomerate wall rock. Compositions of the 

suite of mafic megacrysts indicate derivation from the mantle; thus they are xenocrysts. The alkali olivine basalt composition inferred for the juvenile magma of Black Canyon 

dikes and eruptive units is consistent with these inclusion 

compositions.

The dominant mantle-derived megacrysts are black 

kaersutite (Ti-hornblende) cleavage fragments with ubiquitous reaction textures. Less common xenocrysts are black 

pyroxene grains and polygranular olivine clusters. Small 

xenoliths of spinel peridotite and pyroxenite—including 

amphibole- and mica-bearing types—are present but uncommon; one peridotite contains a kaersutite veinlet with 

compositions similar to most analyzed kaersutite megacrysts. Systematic analyses of kaersutite grains from the 

dike segment with the best-exposed inclusion concentration 

show no compositional variations that can be related to 

grain size, shape, textural relations, or position. Mineral

compositions and textural relations indicate that the mafic 

xenolith-megacryst (xenocryst) assemblage in the Black 

Canyon dikes most likely was derived from an area of upper mantle composed of peridotite with veins of pyroxenite 

and pods of coarse crystalline amphibole. Partial melting of 

this type of assemblage could have produced the dike magma, but the observed reaction textures and isotopic disequilibrium between megacrysts and the dike matrix indicate 

that the suite of inclusions does not represent the actual 

parent material.

Our detailed observations indicate that most internal 

structures in the dikes are concordant with the axial planes 

of the dike segments and are related to flow processes of 

magma in conduits. These structures include: alternating 

zones of massive or fissile matrix (containing longitudinal 

joints), rare flow banding, and the boundaries of matrix 

structure zones, as well as orientations of the long dimensions of vesicles and of mineral and rock inclusions. One 

roadcut through a dike segment exhibits four to five regularly-alternating matrix structure zones in combination 

with a large volume of size-sorted inclusions.

Only three dike segments contain more than 10 percent inclusions. In all these segments the largest volume of 

inclusions—of both mantle and near-surface origin—is 

concentrated in the axial zones; the largest inclusions and 

the greatest size range of inclusions are found in the central zone of the dike. The presence of fanglomerate clasts 

in these axial inclusion concentrations demonstrates that 

inter-grain pressures effectively moved inclusions toward 

the center of the dike conduits. Therefore, axial concentrations of mantle xenolith-xenocryst inclusions are found in 

the dikes where the flowing magma contained a relatively 

large volume of particles. The axial inclusion concentrations and size sorting of inclusions were most likely produced by flow sorting and not by multiple injections of 

magma or progressive crystallization phenomena, which 

have been proposed previously.

INTRODUCTION

Manuscript approved for publication May 12,1993

Alkali olivine basalt dikes and dike-fed tuff breccia 

crop out in an area of approximately 1.5 km2, near U.S.
MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

Highway 93, in the Black Canyon of the Colorado River, 

northwest Arizona. The best-known dike exposure is a 

roadcut located 16 km south of Hoover Dam and the tuff 

breccia is found in a small eruptive center, located at the 

south end of dike outcrops (figs. 1 and 2). The dikes were

114« 37-sell 4°37'36i 114°37'30'

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1 KILOMETER

____I____

0 1 MILE 

CONTOUR INTERVAL 40 FEET

Figure 1. Index map of study area, in northwestern Arizona. Dikes 

are shown in heavy black lines; numbered locations are described in 

table 1 and text. Heavy dashed line represents a jeep trail. Topographic base from U.S. Geological Survey Ringbolt Rapids, Arizona-Nevada quadrangle map, 1:24,000 scale, photorevised 1973.

Figure 2. A, Map showing geology of vent area and southernmost dikes of southern Black Canyon array (location shown in 

fig. 1). B, Map showing the magnetic expression of the vent area, 

superimposed on outcrops of intrusions (location shown in fig. 

2A). Light shading shows main region of domed magnetic anomaly; darker shading is the highest peak on the magnetic anomaly.

35' 

56' 

20'

Abandoned 

roadcuts

Area of C, 

figure 2B

B

EXPLANATION

Alluvium (Quaternary) Tuff and dikes (Tertiary)— 

Mixed rock unit

Tuff breccia (Tertiary) I I Fanglomerate (Tertiary) 

_. sggg ^/ Contour of altitude

Dike (Tertiary) 400"-^ Magnetic contours, dotted

—** where inferred. Hachures 

indicate closed low

0 100 200 300 FEET 

CONTOUR INTERVAL 40 FEET 

MAGNETIC CONTOUR INTERVAL 

400 nanoTeslas
GEOLOGIC RELATIONS IN BLACK CANYON

emplaced in fanglomerate of Miocene and Pliocene age, 

which contains clasts derived from older metamorphic 

rocks and granite of the adjacent mountain ranges.

Roadcuts expose a dike segment with conspicuous 

concentrations of kaersutite megacrysts and rock fragments; inward from the contacts the kaersutite grains increase in abundance and are larger in size. These 

concentrations were called "zoning" by Campbell and 

Schenk (1950), who interpreted the dike as a camptonite 

magma that had crystallized in place. They hypothesized 

that volatile components of the magma had been concentrated in the axial zone of the dike, allowing crystallization 

of coarse kaersutite grains, and that smaller crystals 

formed in the dike margin, owing to the smaller proportion of volatiles in the magma near dike contacts. However, rock fragments also are larger in the dike axial zone, 

and xenoliths of altered peridotite, probably of mantle origin, have been identified in the inclusion suite (Wilshire, 

Schwarzman, and Trask, 1971). Compositions of kaersutite 

and pyroxene megacrysts from the roadcut exposures suggested that these minerals also were derived from a mantle 

source (Best, 1974; Irving, 1977; Basu, 1978; Boettcher 

and O'Neil, 1980; Poland and others, 1980; Garcia and 

others, 1980).

Our detailed study of structures, textures, and inclusion content and distributions in all the exposed dike segments verifies the mantle origin of the mafic megacrysts 

and xenoliths. Thus, the kaersutites did not crystallize in 

place. Moreover, the distribution of inclusions by size are 

more complex than Campbell and Schenk (1950) indicated, and we conclude that neither inclusion concentrations 

nor the size distribution in various dike segments could 

have originated as those authors proposed. We also found 

that longitudinal zones, defined by alternations of massive 

matrix and dike-parallel fissile joints, are ubiquitous and 

that only two other exposed dike segments of the Black 

Canyon arrays contain inclusion concentrations similar to 

those in the well-known highway roadcuts. Therefore, the 

"zoning" observed in the highway roadcut is a coincidence 

of features that occur in various combinations throughout 

the exposures of dikes in Black Canyon.

ACKNOWLEDGMENTS

We especially thank Howard Wilshire who originally 

suggested that "zoning" in the Black Canyon dikes was 

due to flow sorting, and Myron Best whose early encouragement kept us going. WA. Duffield and E.I. Smith provided careful and constructive reviews that led to 

substantial improvements in the manuscript. Determinations of oxygen and carbon isotopic compositions were 

done by L.D. White, through the courtesy of Ivan Barnes 

and J.R. O'Neil. Whole-rock major-element compositions

were analyzed by J. Baker, A.J. Bartel, K.C. Stewart, I.E. 

Taggart, and J.S. Wahlberg. Volatile elements were determined by PR. Klock, G. Mason, H.M. Neiman, S. 

MacPherson, and C. Stone. Dennis Sorg prepared the 

leached rock powders for analysis. Between 1981 and 

1985, field support was provided by Jay Noller, Tova Diamond, and Cynthia Ardito.

Modeling of natural remanent magnetization (NRM) 

was suggested by Bob Simpson, who provided the magnetic susceptibility bridge for those measurements; Ray 

Wells guided us in collection of oriented samples for 

NRM determinations, and those measurements were performed by Vicki Pease. Andrew Griscom provided a magnetometer for traverses of the vent area. Todd Fitzgibbon, 

Linnea Larsen, and Ruby Harper helped with data and 

word processing. Various parts of the study were prompted 

by observations of features in the Black Canyon dikes, 

communicated orally or in reviews by Steve Bergman, 

Ray Binns, Dave Eggler, Mike Garcia, and Frank Spera.

GEOLOGIC RELATIONS IN 

BLACK CANYON

The Black Canyon dikes comprise three distinct arrays 

of discontinuously exposed dike segments. Two subparallel arrays, 1 and 1.5 km long, trend close to due north (fig. 

1). Exposed dike segments in each array are from 61 to 

366 m long (table 1). A third, more dispersed array with a 

northeasterly trend is 1 km long and comprises dike segments 60 to 160 m long (fig. 1). This third set of dikes 

trends into related eruptive deposits and intrusions at the 

south end of the study area (fig. 2).

The Black Canyon dikes intrude gently west-dipping 

Miocene and Pliocene fanglomerate deposits of the Muddy 

Creek Formation. The fanglomerate forms an alluvial 

apron along the west flank of north-trending mountain 

ranges, from which clasts of Precambrian gneiss and granite were derived. Volcanic rocks of early to middle Miocene age underlie fanglomerate west of the dike arrays; 

these rocks are mostly andesite and dacite with subordinate basalt and include dacite airfall and ash-flow tuff 

(Anderson and others, 1972; Anderson, 1978; E.I. Smith, 

written commun., 1988). Mesa-capping flows of aphyric 

basalt locally overlie the fanglomerate and Precambrian 

rocks (Anderson and others, 1972).

The dikes have K-Ar ages of 4 to 5 Ma (Anderson 

and others, 1972), and ages of 3.7 to 5.8 Ma are reported 

for massive mesa-capping basalts (Anderson and others, 

1972). The megacryst-bearing dikes are distinctly different 

in composition and appearance from the bulk of approximately coeval basalt flows (Campbell and Schenk, 1950). 

Thus, the megacryst-bearing dikes probably were not feeders for these mesa-capping flows.
MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA 

Table 1. Characteristics of Black Canyon dikes.

Dike segment 

(see fig. 1)

Description Attitude

Strike Dip

Width (cm) 1

Min. Max.

Length 

(m)

Comments

Short segment, 

outcrops 900 m 

north of highway.

N20°E 79°W 80 150 61 Tabular, with horizontal cooling joints. 

Matrix fissile in axis. Sparse inclusions, 

kaersutite, olivine predominate.

Crops out on 

fanglomerate ridge, 

east of jeep trail; 2 

segments with about 

70-m gap between 

exposures.

N16°E 90° 91 370 213 South end tabular, no zoning. Bulbous

swelling at north end, adjacent to tabular 

segment with 5 massive to fissile zones. 

Abundant inclusions; fanglomerate clasts 

predominate, kaersutite less abundant.

3 to 4 Sinuous, offset from N02°Wto 90° 

north end of N35°E 

segment 2. Segment 

3 is south end, 4 

north end, of dike.

0 1,110 275 Predominantly tabular, 3 interior zones.

Mass of fanglomerate inclusions at contact 

near south end. Sparse inclusions, all in axis 

near north end; kaersutite predominates. No 

size sorting. Bulbous swelling at north end 

near dike tip.

5 to 6 Northernmost N10°E 71°E 

exposure of eastern 

array. West contact 

is not exposed.

0 115 275 Bulbous swelling predominant in outcrop. 

Two asymmetric zones, sparse inclusions; 

predominantly kaersutite. No size sorting.

Northernmost N02°Eto 90° 

exposure of western N15°E 

array.

0 100 183 Tabular, resembles segment 1. Tip exposed 

at north end, near small dam in wash.

7A to 8 Relatively straight N10°E 90° 

segment, some 

unexposed parts.

0 180 152 Tabular, massive contact, fissile axis zones. 

Sparse inclusions; kaersutite predominant. 

No size sorting. Tip exposed at south end.

8 to 9 Relatively long and N20°E 90° 110 280 

straight segment.

366 Tabular, resembles segments 7A to 8. Forms 

large and small dams across 2 washes.

10 to 11A Straight segment, 

but tip at south end 

deflected sharply to 

northwest.

N 90° 0 100 150 Tabular, massive contact, fissile inner zone,

and massive axial zone. No size sorting.

11A to 11 Sinuous segment. N10°Eto 76°W 0 240 

Parabolic tips at N11°W 

both ends.

244 Tabular, 2 asymmetric zones. Small bulbous 

swelling near north end. Sparse inclusions, 

no size sorting. Forms large dam in wash.

11 to 11B Sinuous segment. N05°Eto 90° 

At north end is well N10°W 

exposed parabolic 

tip.

0 255 245 Tabular, no distinct zones or size sorting; 

sparse kaersutite inclusions. Parabolic 

joints concentric to contact in tip exposed at 

north end.

12 Two short segments N25°E 

in large wash 

between highway 

and Station 1.

90° 60 100 200 Tabular and massive. No zones; sparse

inclusions, predominantly kaersutite.

13 Cross section 

exposed in U.S. 

Highway 93 

roadcuts.

N25°E 78°E 115 160 244 Tabular, 5 alternating zones, massive to 

fissile zones. Inclusion concentrations, 

marked size sorting. Highest inclusion 

abundances observed; kaersutite 

predominant.

'All widths measured perpendicular to the local axial plane of the dike.
EXTRUSIVE AND INTRUSIVE MEGACRYST-BEARING ROCKS

EXTRUSIVE AND INTRUSIVE 

MEGACRYST-BEARING ROCKS

VENT AREA

The vent area exposes pyroclastic tuff breccia and irregularly-shaped intrusions (fig. 2A). The apparent subsurface extent of intrusions is defined by a magnetic survey, 

described below. Although the area appears very complex, 

the essential relations can be simply summarized: (1) No 

exposures show interstratification of pyroclastic rocks and 

fanglomerate; and (2) outcrop relations and magnetic 

anomalies indicate that the contact between the fanglomerate and the complex of related volcanic and intrusive 

rocks is steep near the southernmost boundary. This contact defines the margin of the eruptive vent.

Dikes intrude both tuff breccia and fanglomerate in 

the northern part of the vent area. In the southern part of 

the vent area a unit of mixed rocks most likely consists of 

tuff breccia and intrusions, although a part of the exposure 

may be an eroded lava flow remnant (fig. 2A). Irregular 

blocks of jointed aphyric basalt are found locally, and 

these may be accidental inclusions derived from older Miocene lava. However, the most massive dike in the vent 

area, which intrudes the contact between tuff breccia and 

fanglomerate, grades from holocrystalline and inclusion 

bearing to massive and aphyric. Most other outcrops of 

aphyric basalt are poorly exposed, and their relation to intrusions of the vent area remains unclear.

INTRUSIONS

Mafic intrusions that contain kaersutite megacrysts occur throughout the vent area. In the south part of the vent 

area, several dikes intrude the contact between ejecta and 

fanglomerate on the west side (fig. 2A); oval pieces of 

massive aphyric basalt 0.5 to 1 m across are found in 

these intrusions. The matrix of the fanglomerate is reddened at distances as much as 70 cm from the contacts 

with these dikes. The most prominent of the dikes strikes 

N. 25° E. to N. 10° E. and has dips that vary from moderate to steep (as much as 78° southeast). This tabular dike 

contains columnar cooling joints that are perpendicular to 

the dike walls; because of the vertical to subhorizontal 

change in the dike orientation, the columnar joints also 

vary from subhorizontal to subvertical.

A few meters north of the northernmost outcrop of 

tuff breccia, several dikes intrude fanglomerate; a cross 

section of the largest of these dikes is exposed in a wash. 

The chilled contact between the dike and the fanglomerate 

is irregular, and the dike itself has a bulbous shape that is 

roughly oval in cross section (fig. 3). The internal structure is complex, with zones of chilled magma next to 

masses of partly disaggregated fanglomerate. Gradational 

between the areas of chilled magma and fanglomerate is 

peperite-like breccia of magma and sandy matrix from the 

fanglomerate.

TUFF BRECCIA DEPOSITS

The pyroclastic deposits are buff-colored or red to redbrown, massive to bedded mafic tuff breccia; layering is 

crude and localized in the southwestern part of the vent 

area (fig. 2A). Matrix of the bedded tuff breccia is mostly 

clay and arkosic sand that probably derives from fanglomerate. The matrix also includes small grains of kaersutite, 

olivine, and vesicular lava. Clasts include gneiss and granite from the fanglomerate, kaersutite megacrysts as much as 

1.5 cm across, and irregular masses of vesicular lava as 

much as 20 cm across. Some beds contain flattened masses 

of clay, which may be accretionary lapilli. In the southern 

part of the vent area, tuff breccia layers and interleaved sills 

dip 25° to the east. The continuity of dips in all other units 

suggests that the bedded tuff probably was tilted by the 

upwelling intrusive magma. The bedded tuff breccia locally 

is friable, but near intrusive contacts it is metamorphosed to 

a tough, flinty rock.

Massive light-colored tuff breccia that resembles vent 

agglomerate forms a small outcrop in the northern part of 

the vent area. It is composed of angular scoria fragments 

and has a lower content of mafic megacrysts, clay, and sand 

than the bedded tuff breccia. Contact relations between the 

massive and bedded breccia deposits are unexposed.

Figure 3. Bulbous intrusion in fanglomerate at north end of both 

vent area and outcrop; scale given by seated figure in light hat 

(at base). Along the top of the fanglomerate ridge, the dike appears tabular.
MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

MAGNETIC EXPRESSION OF THE VENT AREA

A ground-level magnetic survey was made of the vent 

area to determine the extent and probable shape of the intrusions. Traverses to measure the vertical component of 

the magnetic field were made with a fluxgate magnetometer, from a baseline oriented N. 70° W., located 50 m south 

of the southernmost dike exposure. Approximately northsouth lines of traverse were established at 32-m spacings 

along the baseline. Measurements were made at 50-ft (16 

m) intervals, resulting in a rectangular grid of data points 

over an area 500x400 m. The magnetic background was 

determined to be 250 gammas, from the average readings 

made over fanglomerate along the baseline; values are believed accurate to ±10 gammas (1 gamma=l nanoTesla). 

Data were corrected for diurnal drift by readings taken at 

baseline station 1 at the beginning and end of each traverse.

Magnetic susceptibilities of the dikes were measured 

in the field using a hand-held susceptibility meter. Selected 

samples also were measured in the laboratory with a susceptibility bridge. The natural remanent magnetization 

(NRM) of the samples was measured in the laboratory on 

oriented hand samples. The NRM direction has normal polarity, and for five of the nine samples it points in the direction of the present-day field. Magnetic susceptibilities 

(measured in the cgs system) for all samples range from 

2.6xlO~3 to 17xlO~3. Seven of the nine samples have susceptibilities from 2.6xlO~3 to 4.76xlO~3, with a median 

value of 3.5xlO~3.

A domed magnetic anomaly (average readings between 650 and 1,050 gammas; fig. 25), with steep marginal gradients, was recorded in the northern part of the vent 

area; sharp anomalies peak at 2800 gammas (light and 

heavy shaded areas, fig. 25). The shape of this anomaly 

indicates that exposures are connected to an intrusive body 

or multiple intrusive bodies beneath the vent area; the 

steep marginal gradients indicate that the intrusive mass is 

relatively shallow. Another area of high anomalous values 

(1,200 to 1,600 gammas) was detected in the southern and 

southwestern part of the vent area (light shaded area, fig. 

2E). This southern anomaly is coincident with the outcrops of mixed tuff breccia and intrusions (mixed rocks 

unit, fig. 2A).

The essential features of the measured magnetic field 

in the vent area are represented well by a two-dimensional 

model of a uniformly magnetized body at shallow depth. 

To model the amplitude of the observed anomaly, magnetization values of 5x10~3 were required; these are the 

highest measurements on seven of nine surface exposures. 

The sharp peaks and valleys of the anomaly can be explained by assuming irregularities in the upper boundary 

of the body. We also considered an alternative model of a 

body that consists of a variably magnetized intrusion or 

complex of intrusions, which could explain the essential 

features of the anomaly equally as well.

Bodies 50 and 200 m in thickness were tested in the 

model of a uniformly magnetized body; solutions for each 

body thickness match the essential features of the anomaly. Thus, the data provide few constraints on depth or 

shape of the base of the magnetic intrusive mass.

On the south and west margins of the vent area, the 

400-gamma magnetic contour bounds the two-dimensional 

model body. Steep magnetic gradients at these margins are 

explained well by assuming nearly vertical contacts, which 

may correspond either to faults or steep intrusive contacts. 

However, the east and north boundaries of the vent area 

are modeled best by contacts with relatively shallow outward dips. For a model body with steep contacts, a welldefined magnetic polarization low is expected north of the 

vent area. The absence of this polarization low supports 

the idea that the magnetic body has a northern contact 

with a shallow north dip.

This simple model of a single, uniformly magnetized 

body explains the anomaly. However, we prefer the alternative model of many variably magnetized intrusions because 

it is consistent with field observations, which indicate that 

the magnetic body is a composite of intrusions. Because the 

NRM of dikes in the vent area and the present-day field 

have the same direction of magnetization, the high average 

magnetization used to model the amplitude of the observed 

anomaly can be justified as an effect of additive magnetizations from several individual intrusions.

OBSERVATIONS ON THE DIKE ARRAYS

GEOLOGIC RELATIONS AND STRUCTURES

Three discontinuous arrays of offset dike segments 

crop out north and northeast of the vent area in Black 

Canyon (fig. 1). The southernmost array has predominantly N. 25° E. strikes, and the two northernmost arrays have 

predominantly N. 0° E. to N. 10° E. trends and steep dips 

(75° to 85°) to the east (table 1). Some of the north-trending dike segments are sinuous, with local strikes up to N. 

10° W. (fig. 1). Only one dike segment (between locations 

11 and 11 A, fig. 1) strikes northwest along the entire 

length of exposure. All other Miocene dikes in the study 

area, including mafic and silicic varieties, have northerly 

orientations (Anderson, 1978).

The contacts between dikes and fanglomerate are 

sharp, and all dikes have distinct chilled margins (table 2). 

The fanglomerate shows slight but distinct reddening as 

much as 300 cm from the contacts, owing to the thermal 

effects of dike emplacement. Clasts and sandy matrix that 

clearly came from incorporation of fanglomerate wall 

rocks are found locally in the dikes.

No faults are apparent in the fanglomerate deposits; 

however, numerous north-trending high-angle normal faults 

occur in older Miocene rocks, which are exposed 5 to 10 km
EXTRUSIVE AND INTRUSIVE MEGACRYST-BEARING ROCKS

Table 2. Features of zoned dikes.

[—, no data; n.d., data not determined]

Dike segment Zone 

(see fig. 1)

2 1

2

3

4

3 1

2

3

4 1

2

3

5 to 6 1

2

10 to 11 1

2

3

13X.Y, Z 1

2

3

4

5

Width 

(cm)

1-2

2-5

15-25

HOBO

10-20

70

140

10-25

56-145

25-50

?-20

95

20-43

24-41

87-100

3-13

7-18

18^0

20-40

15-40

Inclusion 

abundance

Sparse to 

barren

Sparse

Abundant

Very 

abundant

Abundant

Sparse

Abundant

Sparse

Sparse

Sparse to 

moderately 

abundant

Sparse

Sparse

Sparse

Barren

Sparse

2

5-6

25-30

13-15

13-40

Inclusion size (mm)

Max.

—

—

0.5-30

5-70

0.1-25

0.8-20

0.1-70

0.5-20

0.5-25

0.3-25

0.2-20

1.0-50

?-20

n.d.

1.5-60

0.5-5

0.5-20

0.5-40

0.5-40

0.5-72

Min.

—

—

n.d.

?-50

n.d.

n.d.-2

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

0.1-2

O.l^t

0.1-6

0.1-6

2-12

Matrix 

texture

Glassy

Glassy to very 

fine grained

Fine grained

Indeterminate

Glassy, 

vesicular

Very fine 

grained

Very fine 

grained to fine 

grained

Glassy to very 

fine grained

Fine grained

Fine grained

—

—

—

—

—

Glassy, 

vesicular

Very fine 

grained, 

vesicular

Fine grained, 

vesicular

Fine grained, 

amygdaloidal

Fine grained, 

amygdaloidal

Matrix 

structure

Massive

Massive

Sparsely 

fissile

Massive

Massive

Sparsely 

fissile

Variably 

fissile

Massive

Variably 

fissile

Fissile

Massive

Fissile

Massive

Fissile

Massive

Massive

Sparsely 

fissile

Highly 

fissile

Massive

Highly 

fissile

Comments

Symmetrical chilled margin.

Inner chill zone.

Zones symmetrical to axis; "braided" 

matrix structure. Kaersutite, olivine 

inclusions predominate.

Axis contains granite, gneiss clasts 

to 70 mm. Less abundant kaersutite 

to 50 mm.

Chilled contact.

Symmetrical to axis.

Axial zone varies irregularly from 

massive to fissile.

Chilled contact. Rare flow banding 

parallel to contact.

Symmetrical to axis, varies in width.

Inclusions concentrated in axial 

zone.

West half of dike; contact not 

exposed.

East half of dike.

Contact and chilled margin.

Zone absent north of location 1 1 A.

Symmetrical contact, in all 

exposures.

Symmetrical in all exposures. 

Contact of zones 1-2 gradational.

Symmetrical to axis in Y, Z; occurs 

W side of axial zone of exposure X.

Symmetrical in exposure Z; absent 

in Y; occurs only E side of axis in 

exposure X.

Axial zone always present; 

gradational to zones 3 and (or) 4.

'Qualitative estimates, except for location 13, for which numbers are mode percents (field mode); see figure 13C.
8 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

west of U.S. Highway 93 (Anderson, 1978). The Black 

Canyon dike and fault trends also are parallel to those of 

nearby mountain ranges and thus probably are parallel to 

unexposed range-front faults. Miocene extension in an eastwest direction is well documented to the west of Black 

Canyon in the nearby Eldorado Mountains of Nevada and to 

the south of Black Canyon in the Colorado River trough 

(Anderson, 1971,1978; Anderson and others, 1972; Howard 

and John, 1987; Faulds and others, 1990). Thus, Black Canyon dike arrays are oriented nearly perpendicular to the 

direction of Miocene extension and parallel to the direction 

of least horizontal stress at the time of dike emplacement.

Most dike segments crop out continuously (fig. 1) and 

are best exposed on the lower slopes of dissected alluvial 

fans, although some outcrops can be followed across interfluves. Gaps along strike occur on ridges where dike crests 

have not been exposed by erosion. Most of the large open 

areas between dike segments are washes with alluvial fill 

and may be due either to the level of exposure or the absence of an intrusion in those areas. Dikes that cross narrow 

washes commonly form sediment dams (table 1; Campbell 

and Schenk, 1950).

With notable exceptions, dikes typically are tabular 

and range in width ("thickness" as defined by Delaney and 

Pollard, 1981) from 80 to 370 cm (table 1). Widths decrease abruptly near the parabolic tips where dike segments pinch out. Few tips are seen in outcrop; the best 

exposed tip is at location 115 (table 1; figs. 1 and 4). At 

locations 2, 4, between 5 and 6, and at 11 the otherwise 

tabular dike segments display bulbous swellings ("protrusions" of Campbell and Schenk, 1950; "buds" of Delaney 

and Pollard, 1981) that are up to 1,110 cm wide (table 1; 

figs. 5 and 6A, B). Bulbous swellings occur both in the 

middle and near ends of tabular segments.

Magnetic anomalies of the thin vertical Black Canyon 

dikes are observed only when the magnetometer is directly

Propagation 

direction

Bulbous swelling 

(Bud)

Figure 5. Idealized dike (from Delaney and Pollard, 1981) based 

on study of northeastern dike at Shiprock, New Mexico, which is 

exposed by erosion to deeper levels than the dikes in Black Canyon. For example, features such as cusps at the join of the main 

dike and uncoalesced segments are not exposed in the Black 

Canyon dike arrays. Parentheses denote terms of Delaney and 

Pollard (1981) not used in this report.

Figure 4. Longitudinal section of 

dike tip at location 11 (fig. 1), 

viewed from above. Internal partings are concentric to the shape 

of the contact (arrow); pencil (p) 

is about 10 cm long.
EXTRUSIVE AND INTRUSIVE MEGACRYST-BEARING ROCKS

Figure 6. ^ A, Dike segments between locations 2 and 4 (fig. 1) 

(north is to left); location 2 is the 

bulbous structure at upper right; location 3 marks site of deflected 

southern tip of a tabular dike with 

bulbous structure at location 4 (described in tables 1 and 2) (telephoto 

view, from a distance of about 0.5 

km). ^ 5, Curved fissile joints in 

bulbous structure at location 5; 

scale shown by figure (and shadow) at left edge of photograph.

over an outcrop. Dikes commonly show magnetic-polarity 

reversals along the length of outcrop, which we ascribe to 

lightning strikes. Magnetic susceptibility measurements on 

samples of dikes north of Highway 93 suggest that they 

have one-half to one-third the bulk magnetization of intrusions in the vent area. We found no magnetic anomalies to 

indicate the presence of multiple dikes or large intrusive 

masses in the subsurface north of the vent area.

Dike segments in Black Canyon are offset, and the ends 

of some offset segments overlap. These relations are best

exposed in the western array (segments between locations 7 

and 1 IB, fig. 1). The cause of offsets between dike exposures 

was discussed by Campbell and Schenk (1950), and a dike 

with similar structure at Shiprock, New Mexico, has been 

studied in detail by Delaney and Pollard (1981; fig. 5).

The tips of adjacent offset and overlapped segments 

commonly are deflected away from each other, and some 

tips have different strikes from the overall strike of the dike 

segment. At location 11, the parabolic tips of two dikes are 

within a few meters of each other; the segment north of 

location 11 and its tip both have northwest strikes. However, 

the segment south of location 11 has a northerly strike on 

average, but its tip is deflected to the northeast (fig. 1). The 

north tip of the dike segment between locations 10 and 11A 

is deflected to the northeast from the main north trend of the 

segment such that the tip trends toward the overlapped south 

tip of the dike segment between locations 8 and 9 (fig. 1). 

The two dike tips are separated by 200 m. In contrast, two 

segments with overall due north trends pinch out at location 

11A, where the overlapping tips are offset 7.6 m; both these 

tips have northwest trends. Deflection of the tips probably 

reflects local stress fields present during intrusion of the dike 

segments, which are branches of a main intrusion at deeper 

levels (Delaney and Pollard, 1981; fig. 5).

Only one tabular dike is offset in the middle of its 

exposed length (about 10 m south of location 8), possibly as a 

result of late Miocene faulting. However, the dike has no 

relief above the ground surface, and the displacement is so 

small (one dike width) that unexposed dike geometry, such as 

two dike tips connected by a small bulbous swelling, could 

produce the apparent offset (Delaney and Pollard, 1981).

INTERNAL FEATURES

With the exception of the dike segment at location 13 

(fig. 1), which is exposed in roadcuts, the internal characteristics of most dikes are seen in longitudinal section
10 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

Figure 7. Fanglomerate incorporation in Black Canyon dike 

segments. ^ A, Breccia of fanglomerate and dike matrix in 

margin of dike at location 2 (fig. 

1) adjacent to bulbous structure; 

contact of dike and fanglomerate 

wall rocks is close to the left edge 

of photograph (arrow); hammer 

lies across a mass of fanglomerate matrix and clasts; below hammer are two lozenge-shaped 

masses of quenched basalt (d); 

dark spots are anhedral kaersutite 

megacrysts. ^ B, Detail of fanglomerate-basalt breccia; lower 

edge of photograph, light-colored fanglomerate clasts in darker matrix of baked sandstone; top 

of photograph, mixed fanglomerate and basalt with large irregular kaersutite megacrysts.

(eroded dike crests); thus, variations along strike can be 

examined more easily than variations with depth. All the 

dikes have chilled contact zones. Massive matrix of the 

contact zones was originally glassy but now is devitrified 

and mostly altered to clay minerals; the axial parts of 

dikes more than 100 cm wide have coarser matrix textures. The marginal and internal matrix of all dikes is variably vesicular and locally amygdaloidal, and vesicles 

locally are flattened parallel to the dike axial plane.

Interior chilled zones are rare and usually occur adjacent to masses of included fanglomerate (fig. 7A, B); at

one site we observed an internal chilled zone that is parallel to the longitudinal contact and appears unrelated to 

fanglomerate incorporation. However, the inclusions in 

this exposure are predominantly centimeter-sized granitic 

clasts, probably from disaggregated fanglomerate.

The thinnest tabular segments (for example, locations 

1 and 12; table 1) and narrow parts of dikes near segment 

tips are predominantly massive in structure and have very 

fine grained to fine-grained matrix texture. Matrix plagioclase laths generally are oriented subparallel to each other 

in a microscopic pilotaxitic texture that is most apparent 

adjacent to megacryst grains.

Both tabular dike segments and bulbous swellings locally exhibit a variety of joints that probably formed at 

different stages of dike emplacement or cooling and that 

interact to form complex patterns. Although some dikes 

have only massive matrix structure (table 1), the interiors 

of most dikes contain variably spaced joints that are oriented parallel or subparallel to the axial plane. When, as is 

common, the joints are closely spaced (1 cm or less), we 

refer to this matrix structure as "fissile" (tables 1 and 2). 

Many dikes also exhibit columnar cooling joints, which 

are perpendicular to the dike walls.

Bulbous swellings have particularly complex internal 

joint patterns, including irregularly alternating fissile to 

massive matrix structure and columnar cooling joints. Orientations of joints in the bulbous structures range from 

horizontal to vertical. Three-dimensional exposures at location 5 (fig. 1) show that the joints that create fissile 

structure define curved internal surfaces (fig. 6B).
EXTRUSIVE AND INTRUSIVE MEGACRYST-BEARING ROCKS 11

STRUCTURE-PARALLEL JOINTS

Zones of massive or fissile matrix structure, formed by 

closely spaced joints, alternate across the width of many 

dikes and may vary irregularly along the outcrop length of 

tabular dike segments. The joint patterns in these segments 

locally resemble currents in flowing streams (fig. 8). In 

most exposures, zone margins are parallel or subparallel to 

axial planes of the dikes; locally the zones may be symmetrical to the axial plane, but arrangements can change to 

asymmetrical in a short distance along strike (table 2; fig. 

9). Near location 4, we observed flow banding in glassy 

matrix at the contact between the chilled margin and the 

next zone inward (zone 2), which contains fissile joints 

(table 2; fig. 10). We believe that the fissile jointing is inherited from flow banding, which is rarely preserved in the 

devitrified matrix.

In the dike tip at location 11 (table 1), fissile joint 

structure parallels the parabolic shape of the tip (fig. 4); 

this relation is the only one in which fissility lies at a high 

angle to the axial plane and supports an origin of these

joints as shear planes in late-stage flow patterns of the intruding magma.

A few tabular dike segments have three to five regularly alternating massive or fissile zones, but such regular 

zonations continue along strike for only a few meters. 

Zones merge gradationally; therefore, recorded zone 

widths (table 2) are measurements based on arbitrary, but 

consistently applied, boundary criteria. Zones are numbered for convenience in this discussion: zone 1 is always 

the chilled contact, and zones 3, 4, or 5 may be axial.

The dike segment between locations 3 and 4 contains 

three zones that all vary in character along strike (table 2). 

Near location 3, the dike has a massive contact zone (1), a 

massive to fissile inner zone (2), and a variably fissile axial 

zone (3). Near the north end (location 4), zone 2 is variably

Figure 8. Dike having irregularly interspersed massive 

and fissile matrix zones with stream-flow appearance; 

view of longitudinal section from above. Width of area 

depicted is about 100 cm.

Figure 9. Block diagram of roadcut sections across dike segment at location 13 (fig. 1), showing the gradational variations 

of structural zones between exposures X, Y, Z (also see table 2 

and fig. 11A, B). Pattern of ovals and dots denotes fanglomerate 

country rock. Numbered zones correspond to descriptions in table 2. Dike chilled margin (zone 1) is unpatterned, massive 

zones 2 and 4 are shown in gray and black stipple, respectively. 

Lined patterns represent finely fissile zones—narrow pattern 

depicts zone 3, and wide pattern is coarsely fissile zone 5.
12 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

fissile and the axial zone is entirely fissile. The dike segment near location 2 contains a fissile axial zone (3), which 

lies between the dike's central zone (zone 4) and a finegrained zone (2) inboard of the chilled contact. This fissile 

axial zone meanders longitudinally in a braided-stream 

fashion.

The single dike segment at location 13 is exposed by 

two parallel roadcuts that trend nearly perpendicular to 

strike of the dike; no other segments have comparable vertical or lateral exposure (figs. 1, 9, HA, E). The roadcut 

sections are labeled X, Y, and Z, from southwest to northeast (figs. 1 and 9); exposures Z and Y are opposite faces 

of the same roadcut (fig. 9). This dike segment contains as 

many as five massive and variably fissile zones that range 

from 3 to 40 cm in width (table 2).

Zones of the dike segment at location 13 vary in 

width, occurrence, and arrangement between exposures. In 

exposure Z all the matrix zones are present and arranged 

symmetrically around the coarsely fissile dike axis (zone 

5). However, the massive internal zone (4) is absent in 

exposure Y (table 2; fig. 9). In exposure X, all zones are 

present but are arranged asymmetrically—the fissile zone 

(3) occurs only on the west, and the massive zone (4) only 

on the east, side of the dike axis. Different asymmetrical 

arrangements of zones are observed in other dike segments. For example, in the tabular part of the segment beFigure 10. Photograph of flow banding in margin of 

dike at location 4 (fig. 1). Pencil (10 cm length) defines 

vertical orientation. Long dimension of kaersutite megacryst (left of pencil) is oriented parallel to banding and 

dike wall. To right (east) of pencil the matrix contains 

closely spaced fissile joints.

Figure 11. Photographs of dike segment at location 13. A, 

Exposures of dike seen from the south side of U.S. Highway 93. Exposure X is on the modern highway and exposure Z can be seen in old roadcut beyond; exposure Y 

faces Z in old roadcut (see fig. 9). B, Detail of exposure Z 

showing chilled margins and internal zones (table 2).
EXTRUSIVE AND INTRUSIVE MEGACRYST-BEARING ROCKS 13

tween locations 5 and 6 and also between locations 10 and 

1L4 (fig. 1), a fissile zone 95 cm wide forms the east side, 

whereas the west side of the dike is massive in structure.

COOLING JOINTS

Columnar cooling joints are common within the dikes. 

The columns are generally observed on vertical dike walls 

as polygons 20 to 50 cm across (fig. 12A). However, in 

the dike segment at location 1, interior horizontal to subhorizontal joints with smaller polygonal dimensions occur 

at the contact between chilled margin and the axial zone. 

At locations 7, 9, and 11 (fig. 1) small-scale vertical columnar joints occur in the exposed (and eroded) dike crest

Figure 12. Static cooling joints in Black Canyon dike segments. 

A, Horizontal cooling joints, expressed as polygons on dike wall 

at location 1 (fig. 1). B, Dike at location 7 (fig. 1) showing vertical polygonal cooling joints (photograph is oriented nearly parallel to strike of dike).

(fig. 12/?), suggesting that the top of this outcrop is within 

a few centimeters of the original upper contact of the dike.

INCLUSION SUITE

All segments of Black Canyon dikes, as well as intrusions in the vent area, contain irregular inclusions of shiny 

black kaersutite. Other minerals observed or reported as 

inclusions are altered (rarely fresh) olivine, black clinopyroxene, magnetite, milky plagioclase, alkali feldspar (sanidine and anorthoclase; Poland and others, 1980), and 

quartz. Although usually called "megacrysts," measured 

kaersutite and pyroxene grains range in size from less than 

0.1 mm to as much as 100 mm.

Kaersutite grains normally display cleavage shapes, although many large grains have embayed, irregular outlines 

(fig. IB). Relic deformation textures identify large, unaltered olivine grains as xenocrysts rather than phenocrysts. 

Pyroxenes have oval or circular shapes, although a few 

grains that we analyzed appear euhedral.

Melt and reaction textures are ubiquitous. Plagioclase 

and quartz grains have spongy margins, probably owing to 

incipient melting, and many contain cavities with glassy 

margins, indicating a more advanced stage of melting in 

the host magma. Locally, large and small kaersutite and 

clinopyroxene grains have reaction rims, and some kaersutite grains appear to be largely fused. Fused areas in kaersutite grains are altered to fine-grained opaque material, 

and some enclose small birefringent patches of unfused 

amphibole. Large amphibole grains commonly show meltinduced fragmentation—grain margins are serrated, and 

grain splinters, although surrounded by matrix, lie alongside and in optical continuity with the parent grains.

Xenoliths of the inclusion assemblage comprise a mafic and ultramafic suite of altered wehrlite and dunite (interstitial pargasite), spinel Iherzolite with rare unaltered 

diopside, and pyroxenite, including magnetite- and kaersutite-bearing pyroxenite (A.J. Irving, written commun., 

1982). Evidence of a mantle origin for this mafic-ultramafic suite is presented and discussed in following sections.

Felsic rock types among the inclusions are granite, 

pegmatite, aplite, and various kinds of gneiss. The felsic 

rocks and some felsic mineral inclusions, such as quartz 

and possibly K-feldspar, might be derived from lower 

crustal levels traversed by the magma conduits. However, 

the felsic inclusions are similar to the mixed gneiss and 

granite clast types found in the host fanglomerate. Because 

partly disaggregated fanglomerate masses are observed 

commonly in the dike exposures, we believe that the fanglomerate is the most probable source of felsic inclusions.

INCLUSION ORIENTATION AND FOLIATION

Some dike segments with abundant mineral and rock 

inclusions have a foliation that is defined by the preferred
14 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

orientation of matrix plagioclase laths, equant sections of 

tabular inclusions, and long dimensions of flattened vesicles. In tabular dikes this foliation is generally parallel to 

the axial plane of the dike segment and thus is generally 

parallel to the planes of fissile joints. Vesicles are rare in 

fissile zones. In the plane of foliation, plagioclase laths do 

not define a consistent lineation but generally are oriented 

tangential to the boundaries of inclusions and vesicles.

Most inclusions, both megacrysts and xenoliths, are 

tabular. In the dike segment at location 13, the shortest 

triaxial dimension of inclusion grains is about half of the 

longest dimension and is oriented approximately perpendicular to both the dike axial plane and the foliation. Regardless of the dike segment dip direction (fig. 13A), long 

dimensions of inclusions are parallel or subparallel to the 

dip of the dike axial plane. This alignment of inclusion 

long axes is very prominent in every zone, except the 

chilled contact zones. Observed inclusion shapes are nearly equant in the plane of foliation and do not form a measurable lineation.

In the dike segment at location 13, all features that 

parallel the axial plane, including fissile joints, boundaries 

between fissile and massive matrix, inclusion concentrations, flattening of vesicles, and orientation of the longest 

dimensions of both matrix minerals and inclusions (table 

2) are superimposed, perhaps coincidentally.

INCLUSION DISTRIBUTION PATTERNS

Most of the dike segments contain sparse inclusions 

with maximum dimensions between 0.5 mm and 100 mm; 

grains of all sizes are randomly distributed within the two 

or three most commonly observed patterns of dike structure zonation (table 2, and above). However, three of the 

dikes that contain a large number of matrix structure zones 

also contain abundant inclusions that are sorted symmetrically by size with respect to the dike's axial zone. This 

symmetrical size sorting is observed in dike segments near 

location 2, in the segment between locations 3 and 4, and 

in the roadcut sections at location 13 (table 2). In each of 

these locations, the greatest volume, as well as the largest 

size of inclusions, is concentrated in axial zones.

Because roadcut sections at location 13 (fig. 1) provided the best exposure of any dike segment, detailed, quantitative measurements of inclusion abundance, mode, size, 

and shape, were made only at this location. Inclusion abundances for location 13 are listed in table 2 as minimum and 

maximum mode percent for the three roadcut sections. 

Abundances listed for other dike segments (table 2) are 

qualitative estimates, recorded as barren (no inclusions 

seen), sparse (up to 5 mode percent), abundant (5 to 15 

mode percent), and very abundant (greater than 15 mode 

percent). Inclusion abundances, types, sizes, and size ranges in table 2 are referred to the structural zones as a matter

of convenience and should not be regarded as implying a 

genetic connection.

In the dike segment near location 2, granite and gneiss 

clasts (fanglomerate derived) are the most abundant inclusions (table 2) and are concentrated in the dike axis 

(roughly corresponding to zone 4) and the adjacent fissile 

zone 3. No inclusions were observed in the chilled contact 

zone, and zone 2 contains only a few small inclusions. Localized between sparsely fissile zone 3 and the axial zone 

is a peperite-like breccia, which is composed largely of 

fanglomerate clasts and lumps of sandy matrix but which 

also includes anhedral kaersutite megacrysts as much as 

30 mm across, olivine grains 10 to 25 mm across, and 

clasts of nonvesicular dike matrix (fig. 1A, B).

Inclusion concentrations and sizes vary along the 

strike of the dike segment between locations 3 and 4. Near 

location 3, abundant inclusions occupy both contact and 

axial zones. A few meters to the north of location 3, inclusions are concentrated only in the axial zone, and the marginal zone is nearly barren. Near location 4, however, 

inclusions are of lower abundance in all zones, although 

the axial zone contains a slightly larger volume of inclusions than the other zones (table 2). Close to location 3, 

inclusions are as much as 70 mm across in the axial zone, 

and the other zones contain particles less than 25 mm 

across. Near location 4, inclusions of all sizes are distributed across all the zones.

In the roadcut exposures at location 13 (figs. 1, 9, 

11A, B), each of the zones contains a range of inclusion 

sizes. Inclusions are small and sparse in the two outermost 

zones (<10 mm in zone 1, <20 mm in zone 2; fig. 13B). 

Zones 3, 4, and 5 have moderate to high inclusion concentrations, which vary within the zones, but abundances are 

greatest in zone 3 (table 2; fig. \\E). The size of the largest inclusions and size ranges of inclusions both increase 

progressively toward the axial zone (5) (table 2; fig. 13B). 

Although the symmetry of fissile zone 3 and massive zone 

4 vary between the three exposures and zone 4 is not 

present in exposure Y, the symmetrical distribution of inclusion sizes does not change between exposures (table 2; 

fig. 135).

The field mode (fig. 13C) shows that kaersutite is the 

main mineral inclusion at location 13. Olivine is the next 

most abundant inclusion but is very subordinate to kaersutite. Variations in megacryst/matrix proportions shown in 

figure 13C (circle with dot) are due entirely to variations in 

the abundance of kaersutite grains, because other components are either minor or have nearly constant abundance 

across the dike. These minor constituents are pyroxene, 

magnetite, plagioclase, alkali feldspar (sanidine and anorthoclase; Poland and others, 1980), and quartz (also see 

Irving, 1977; Garcia and others, 1980). Lithic fragments of 

granite, gneiss and peridotite also are present in the dike 

segment at location 13. Like the mineral constituents, the 

largest rock fragments also are found in zone 5.
EXTRUSIVE AND INTRUSIVE MEGACRYST-BEARING ROCKS 15

RELATION OF INCLUSIONS AND BULBOUS SWELLINGS

Bulbous swellings in dike segments commonly are associated with high inclusion abundances—particularly near 

partially incorporated fanglomerate pods. The relation between incorporated fanglomerate and bulbous swellings is 

exhibited at locations 2, 4, south of location 11 (fig. 1), 

and in the vent area intrusion pictured in figure 3. The 

bulbous swelling at location 2 (fig. 7) is continuous with a 

tabular dike segment that contains gneiss and granite

Exposure Z

N

10 20 30 40 50 60 70 

LONG DIMENSION (mm)

48 12 16 20 24 28 32 36 40 

SHORT DIMENSION (mm)

Figure 13. Inclusion orientation, size distribution, and abundance in dike segment at location 

13, exposures X, Y, Z. A, Rose diagram showing dips of inclusion long dimensions (measured on vertical surfaces perpendicular to 

strike); total of 787 grains. B, Distribution of 

long and short inclusion dimensions (plotted 

with respect to structural zones); same data set 

as 13A. C, Field mode of mineral and lithic 

fragments (total of 8,500 grains); for each exposure, modes were counted on two traverses approximately perpendicular to strike of dike; mineral symbols are 

positioned at average value for six traverses; bars show range of values for all traverses (if greater than size of symbol); 

mineral symbols: circle with dot, ratio of inclusions to matrix counts given as a percentage; diamond, kaersutite; filled 

circle, olivine; square, feldspar grains; open circle, clinopyroxene; triangle, ultramafic xenoliths.
16 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

clasts concentrated in the axis and contains a marginal 

breccia of mixed fanglomerate and chilled matrix. At location 4, the dike contact zone contains masses of fanglomerate (fig. 14). Near location 11, the intersection between 

the tabular part of the dike and a small bulbous swelling 

(table 1) is very sharp. The tabular part contains a small 

volume of mixed gneiss clasts, which probably were derived from fanglomerate. Only the large bulbous swelling 

near location 5 shows no clear relation to incorporation of 

fanglomerate wall rocks.

COMPOSITION OF DIKES AND 

INCLUSIONS

PETROGRAPHY AND COMPOSITION OF DIKES

The holocrystalline, aphyric matrix of the Black Canyon dikes comprises plagioclase+altered olivine+altered 

Ti-augite+magnetite. Samples taken from each structural 

zone at location 13 have plagioclase laths that range in 

size from less than 0.1 mm long in the chilled contact 

zone (zone 1) to 0.5 mm long in the axial zone. Grains of 

matrix olivine are equant and have a size range similar to 

the plagioclase, whereas Ti-augite and magnetite grains 

are smaller than 0.1 mm throughout the dike. Carbonate 

alteration pervades the matrix; in addition to calcite, 

patches of analcite, zeolite, and clay minerals are common. Many amygdules and cracks are filled with calcite 

and analcite.

Major-element analyses and calculated norms in table 

3A represent three samples (DS-1, -6, and -12) from the axes

of thin, massive dike segments with no visible inclusions 

(dike locations 1,6, and 12, fig. 1) and one sample (DS-Y2) 

from the massive zone 2 of exposure Y at location 13 (table 

2), which is relatively barren of inclusions. The average bulk 

compositions of these matrix samples (table 3) are obscured 

by alteration and the possible presence of microscopic inclusions; also, the original magma compositions may have varied. Samples DS-1, -12, and -Y2 were analyzed untreated 

(R) and after leaching (L) with dilute HC1 to assess the effect 

of alteration (table 3A). Analyses of matrix from Campbell 

and Schenk (1950) (C-S, table 3A), Alibert and others (1986) 

(A-M-A, table 3A), and Daley and DePaolo (1992) (D-D, 

table 3A) are included for comparison. Sample D-D was 

collected at location 13, and it is likely that the C-S sample 

was also collected at that site, either from exposure Y or Z of 

the old roadcut. The dike sampled by Alibert and others 

(1986) was described as aphanitic and containing rounded 

kaersutite megacrysts (of unspecified dimensions); it probably is not from the segment exposed in roadcuts at location 

13. Normative minerals were calculated for the all samples 

using program PETCAL (table 3A).

Comparison between analyses of leached and untreated 

dike matrix and examination of the normative minerals in 

table 3 suggest that the compositions of samples DS-1R, 

-12R, -Y2R, and -6 are closest to the composition of the 

Black Canyon juvenile dike magma—probably alkali olivine basalt. The unleached compositions of all four samples 

have normative olivine; three of them (DS-1R, -12R, -6, as 

well as A-M-A and D-D) also show nepheline in the norm 

and thus are alkalic in composition. These compositions 

agree with the alkalic compositions of matrix clinopyroxene 

grains, which are difficult to analyze owing to widespread

Figure 14. Mass of fanglomerate 

(outline) engulfed by dike matrix 

near dike contact at location 4 

(fig. 1). Daypack in lower part of 

photograph is about 0.5 m in 

height.
COMPOSITION OF DIKES AND INCLUSIONS 17

Table 3. Compositions of dike matrix.

[Analyses by X-ray fluorescence, unless otherwise indicated; A.J. Bartel, J.S. Wahlberg, J.E. Taggart, J. Baker, K.C. Stewan, analysts. R, raw, or untreated dike 

matrix; L, matrix leached in dilute HG prior to analysis (preparations of treated samples by D. Sorg); —, mineral not present in the norm]

A. Whole-rock major-element analyses.

Sample DS-1

R(2)

PS-12 DS-Y2

R(2) R(2)

DS-6 C-S A-M-A D-D

Analyses (weight percent oxide)

SiO2 — -

A12O3 ~

FeO1 —

Fe2032 -

MgO —

CaO — -

NajO —

K2O — -

TiO2 — -

P205 ~~

MnO —

H2O+ —

H2O' —

CO2

Total -

45.0

15.6

4.59

5.05

5.1

9.1

4.0

2.8

2.9

0.80

0.16

1.36

0.63

1.98

99.07

49.6

14.5

5.18

5.14

5.0

7.1

3.3

2.4

3.3

0.32

0.16

1.76

1.32

0.03

99.11

44.9

15.6

5.23

4.21

5.0

9.6

3.2

2.8

2.9

0.79

0.16

2.80

0.47

1.87

99.53

48.5

14.9

5.60

4.38

5.3

6.9

2.9

2.5

3.2

0.39

0.15

2.65

1.30

0.01

98.68

43.1

15.2

3.88

5.39

5.5

9.7

2.6

1.9

2.8

0.76

0.15

2.64

2.05

3.00

98.67

47.7

14.9

4.27

6.06

4.8

7.0

2.4

1.8

3.3

0.22

0.15

3.06

3.15

0.09

98.90

45.6

15.4

5.82

3.73

5.3

9.1

3.2

3.1

3.0

0.82

0.16

2.48

0.83

1.50

100.04

43.79

17.84

3.95

4.20

9.45

10.44

5.30

1.%

2.48

0.54

0.04

3.93

2.72

2.99

99.96

46.16

15.71

—

10.07

4.62

8.20

4.51

3.22

2.93

0.92

0.17

(LI 3.21)

99.67

44.30

14.95

6.55

1.82

3.86

8.44

3.23

2.87

2.89

0.76

0.15

(LI 9.1)

98.81

Normative minerals (weight percent)6

Ap ------

j| ___

Mt

Or— — -

Ab — —

An

Di .......

Hy ------

Ol— — -

Ne — —

Q .......

Hm

1.95

5.79

7.27

18.42

17.18

19.30

—

3.09

9.30

0.30

0.77

6.53

7.76

14.77

29.08

18.39

12.56

7.26

_

f\ Q£

———

1.94

5.83

6.47

17.53

18.42

21.12

18.83

—

5.56

—

0.95

6.41

6.71

15.60

25.91

21.38

9.51

11.2

_

2.31

—

1.93

5.84

5.36

li.. J*T

24.18

26.59

16.23

0.04

*J*4*J

2.22

0.55

6.76

5.06

11.49

21.93

26.53

7.33

9.51

_

7 78

3.05

1.99

5.98

5.68

19.23

18.379

19.426

17.77

—

f. no

5.45

—

1.25

4.71

5.67

H CO

2.77

19.10

22.70

0.69

9.12

0.29

2.21

0.38

—

19.71

27.33

13.58

9.70

—

5.20

6.61

10.43

1.96

6.11

2.94

10 00

21.67

19.83

17.32

—

f C1

4.74

—

'Gravimetric determination for samples DS-1, DS-12, DS-Y2, and DS-6, H.M. Neiman, G. Mason, P.R. Klock, C. Stone, S. MacPherson, analysts. (2) 

designates average of two determinations for unleached (R) samples. Calculation of value for sample D-D given in Daley and DePaolo (1992)

*)

For samples DS-1, DS-12, DS-Y2, Fe2O3 value calculated: FeO gravimetric determination subtracted from total Fe determined by X-ray spectrography. For 

sample A-M-A total Fe is given as Fe2O3 .

3Analysis from Campbell and Schenk (1950); all oxides by gravimetric determination.

4Analysis from Alibert and others (1986); authors also report minor and trace element compositions, including rare earth elements. LI, loss on ignition. 

Analysis TID-1 from Daley and DePaolo (1992); note that isotopic composition reported under this sample number was determined on an amphibole 

megacryst (E. Daley, oral cornmun., 1993). Total given here omits Cr2O3 (0.012 weight percent). LI, loss on ignition. 

All norms calculated with program PETCAL, written by Richard Koch, U.S. Geological Survey.

alteration (table 4; analytical technique described in table 

caption). The clinopyroxene grains are augite with high titanium and iron contents (TiO2, 3.4 to 4.7 percent) and Mgratios [Mg/(Mg+EFe)] between 0.71 and 0.76.

Unleached samples are rich in CaO (9.1 to 9.7 percent) and samples for which volatiles were determined are 

also rich in CO2 (1.9 to 3.0 percent), whereas both these

components are reduced significantly in the leached equivalents. Also, A12O3 and Na2O contents are reduced as 

much as 1 percent by leaching. All leached samples contain normative hypersthene+quartz and thus appear to be 

subalkaline. Whether leached or unleached, samples of 

dike matrix from location 13 (Y2R, Y2L, C-S and D-D) 

all contain normative hypersthene.
18 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA 

Table 3. Compositions of dike matrix—Continued.

B. Stable isotope compositions of carbonate in dikes, inclusions, and fanglomerate wallrocks.

Sample No. BC-C1 BC-C2 BC-C3 BC-C4 BC-C5 BC-C6 BC-C7

.3.97 

+34.73

Yield (pet)-- 62.4

-1.74 

+32.46

83.3

.5.62 

+38.58

69.8

+1.45 

+22.59

85.1

+0.61 

+20.79

91.3

+0.11

+22.78

1.0

1 Analyses by L.D. White, courtesy of I.R. Barnes.

2 Analyses courtesy of J.R. OTMeill.

Samples:

Cl—Fanglomerate 20 m from nearest dike.

C2—Amygdule in dike axis (exposure Z).

C3—Partly assimilated fanglomerate mass in dike.

C4—Kaersutite megacryst.

C5—Tuff breccia.

C6, C7—Amygdules in massive dike, vent area.

We suggest that the subalkaline compositions reflect 

either removal of important constituents by the leaching 

or—in the case of location 13—unavoidable contamination by the ubiquitous inclusions, particularly by silicic 

components. Because the compositions of leached samples 

change from alkalic character toward compositions incompatible with the modal mineralogy, we suggest that most 

of the CaO in matrix carbonate was derived from the dike 

minerals by reaction with near surface waters and was not 

added by alteration after intrusion. Therefore, removal of 

carbonate by leaching samples before analysis produces 

false matrix compositions.

The isotopic compositions of carbon and oxygen in 

the matrix carbonate (table 3-3) usually resemble values 

typical of sedimentary rocks (6 C of +1.45 to -1.74; 

6^0 of +20.79 to +38.58). One carbonate sample from a 

partly disaggregated clump of fanglomerate within the 

dike segment near location 2 (fig. 1) produced a 613C of 

-5.62, which resembles some values of carbonatite and diamond but also overlaps values reported from sedimentary 

rocks. We suggest that this dike segment is now in equilibrium with ground water isotopic compositions as a result 

of isotopic exchange during late-stage alteration at the 

time of crystallization or during later weathering, or both. 

If any of the carbonate originally had a mantle origin, as 

suggested by M.O. Garcia (written commun., 1984), it 

cannot now be discerned.

Basu (1978) determined 87Sr/86Sr of 0.703991.00008 

for a leached sample of dike matrix, and Alibert and others 

(1986) obtained a similar value of 0.7037891.000038; these 

values resemble Sr-isotopic ratios of most alkali basalts. 

Poland and others (1980) found a value of 0.70456 for 

untreated whole rock and a value of 0.70316 for the same 

rock after leaching with HC1; the Sr-isotopic composition 

of the soluble fraction resembled that of CaCO3 from 

amygdules. Poland and others (1980) concluded that these 

results are consistent with derivation of carbonate from

crustal sources, consistent with the near-surface characteristics of stable isotopes that we report.

COMPOSITIONS OF MAFIC INCLUSIONS

Ultramafic and mafic xenoliths and megacrysts of 

mantle origin are uncommon, but most are found in mafic 

alkalic intrusions or ejecta (Ross and others, 1954). We 

determined compositions of mafic megacrysts and minerals from mafic and ultramafic inclusions in the Black Canyon dikes to determine whether the mafic-ultramafic suite 

derives from the same or a variety of mantle regions.

All analyzed megacrysts but one are kaersutite or clinopyroxene grains, and most are from the roadcut at location 13. Samples from a few other dikes were included for 

comparison. Most of the clinopyroxene samples are black, 

glassy, and have irregular shapes. We did not observe any 

orthopyroxene megacrysts and none are reported in the literature. Two small kaersutite grains (matrix size) were analyzed for comparison with larger grains. From an intrusion 

in the vent area, we found one olivine megacryst that was 

fresh enough to analyze.

To test the hypothesis of F.J. Spera (written commun., 

1984) that some of the kaersutite particles could be phenocrysts of the dike magma, we also sought amphibole 

grains that could be identified as euhedral (having regular 

outlines, uncontrolled by cleavage). We found five candidate euhedral grains during several traverses of every dike 

segment in the three Black Canyon dike arrays; three of 

these inclusions proved to be amphibole (EG, table 6) and 

two are augites. In numerous thin sections, we saw no 

compositionally zoned amphibole grains, such as those 

mentioned by F.J. Spera (written commun. 1984).

Mafic to ultramafic xenoliths found in the Black Canyon dikes represent a variety of rock types and have various textural relations:
COMPOSITION OF DIKES AND INCLUSIONS 19

1. Altered Iherzolite xenoliths are light-green granular 

masses containing relatively fresh chrome-diopside and 

brown orthopyroxene (tables 4, 5, and 7; see also living, 

1977; Garcia and others, 1980). Some of the Iherzolites 

contain interstitial kaersutite, and we observed two composite Iherzolites with thin kaersutite veins. One analyzed 

sample (BC-2-21, tables 5 and 6) contains a 1- to 5-mmwide vein of orthopyroxene+kaersutite.

2. Red-brown altered olivine clusters (wehrlitic xenoliths) are altered olivine grains poikilitically enclosed by 

black Ti-clinopyroxene±amphibole (possibly "pargasite 

wehrlite" of Irving, 1977). Analyses of clinopyroxene and 

amphibole from wehrlitic xenoliths are in tables 4 and 7, 

respectively.

3. Al-augite pyroxenites are granular masses that may 

also contain orthopyroxene and intergrown kaersutite (Irving, oral commun., 1982). We found small pyroxenite xenoliths but were unable to collect or analyze them.

4. Kaersutite grains poikilitically enclose biotite and 

apatite grains (KPA, tables 6 and 9), in clusters that could 

represent xenoliths or glomerophenocrysts. KPA aggregates have been reported as glomerophenocrysts from other xenolith and megacryst localities (for example, Irving, 

1974); such intergrowths are a well-known association in 

veins and (or) pods in both alpine peridotites (ConqueYe, 

1970; Spray, 1982; Mukasa and others, 1991) and peridotite xenoliths in basalts (Wilshire and Trask, 1971; Best, 

1974, 1975; Wilshire and others, 1980).

Complete analyses of kaersutites from the dike segment at location 13 have been published previously (table 

8) by Campbell and Schenk (1950), Garcia and others 

(1980), and Boettcher and O'Neill (1980). Irving (1977), 

Basu (1978), and Poland and others (1980) published partial analyses of a wide range of megacrysts.

OLIVINE

The granular olivine cluster analyzed (table 9) lacks 

strain lamellae and probably is a recrystallized megacryst. 

Because of the widespread alteration, ours is the only olivine analyzed from the Black Canyon dikes. The forsterite 

content of this sample (Fo79; CaO, 0.35 percent) is near the 

middle of the range (Fo70 to Fo84) reported for olivine 

megacrysts from alkalic lavas in the western United States 

and worldwide (Binns and others, 1970; Wilkinson, 1975; 

Fodor, 1978). However, chemical compositions of xenocryst and phenocryst olivines may be indistinguishable; for 

example, Wilkinson (1975) reported an alkalic sill that contains an olivine xenocryst with Fo77 9 to Fo83 9, Ti-augitebearing peridotite nodules with olivine compositions of 

F°76.4 to F°85.9» and groundmass olivine of Fo77 8 to Fo8g.

PYROXENE

Peridotite xenoliths of the inclusion suite contain both 

diopsidic and augitic clinopyroxenes, whereas all clinopyroxene megacrysts are Ti-augites (table 4). In the pyroxene 

quadrilateral (fig. 15), clinopyroxenes from Iherzolite xenoliths in the Black Canyon dikes are diopside to subcalcic diopside. Compositions of poikilitic clinopyroxene 

grains in wehrlitic xenoliths overlap the megacryst compositions, and both the poikilitic grains and the clinopyroxene megacrysts have trends from diopside toward Feenriched augite (fig. 15; table 4).

The distinction between Iherzolite and wehrlite clinopyroxene compositions persists for important nonquadrilateral components (table 4). Diopsides from Iherzolite are 

chrome-rich (0.46 to 1.1 percent Cr2O3 ) and low in Ti and 

Al (0.31 to 0.71 percent TiO2; 4.3 to 6.1 percent A12O3). 

Poikilitic clinopyroxene grains have low chrome contents 

(0.13 to 0.16 percent Cr2O3) but high Ti and Al contents 

(TiO2, 0.71 to 2.0 percent; A12O3 , 4.5 to 8.1 percent). In 

contrast, chrome contents of clinopyroxene megacrysts are 

moderate (0.30 to 0.57 percent Cr2O3), and ranges of Ti 

and Al values are relatively restricted (TiO2, 1.7 to 2.0 

percent; A12O3, 7.2 to 8.0 percent). The large compositional range of Ti and Al in poikilitic clinopyroxenes fills the 

gap between the compositions of megacrysts and grains in 

Iherzolite.

Roden and Shimizu (1989) reported an even larger 

range in TiO2 content (1.9 to 4.4 percent) for clinopyroxene grains from xenoliths with refractory compositions 

(Group I) collected from Black Canyon ("Hoover Dam")

Fs

Figure 15. Quadrilateral components of pyroxene minerals in 

the Black Canyon dikes (calculated values of Wollastonite 

(Wo), Ferrosilite (Fs), and Enstatite (En); data from tables 4 

and 5); shaded area shows location of plot volume between En 

and Di (Diopside) in pyroxene composition triangle. Mineral 

symbols: dots, clinopyroxene megacrysts; triangles, clinopyroxene in Iherzolite; open squares, poikilitic clinopyroxene in 

wehrlitic xenoliths; filled squares, orthopyroxene in Iherzolite; 

diamond, orthopyroxene in vein of composite xenolith sample 

BC-2-21 (table 5).
20 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

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! j | j j ! j i j m

! ! j j j ! ! j j ^j

i i i ! i i ! ! ! ^^

j i i i j j i i u

1 ' <s { | i i j j J2

g» ej g ! ! ' ' 'pi

«^^«SPfld2« £
Table 7. Compositions of amphibole (pargasite) in xenoliths of Black Canyon dikes—Continued.

Interstitial amphibole in Iherzolite (L)

Sample No. LA1 LA2 LA3 LA4 LAS LA6 LA7 LAS LA9 LAID 

Analyses (weight percent oxide)

SiO2 — — — -

A12O3 — — —

FfeO 1011 ----- 

MgO --— -

PaO

Na2O— — — - K- n

TiO 2 — —— — 

Cr203 .........

Total - — 

Mgratio= 

Mg/(Mg+SFe)

42.1 

14.9 

6.2 

15.7 

11.7 

2.7 

1.3 

3.3 

0.74

98.64 

.82

42.1 

15.0 

6.1 

15.7 

11.8 

2.6 

1.3 

3.3 

0.74

98.64 

.82

42.0 

15.0 

6.2 

15.7 

11.7 

2.7 

1.3 

3.3 

0.71

98.61 

.82

42.1 

14.8 

6.2 

15.8 

11.8 

2.6 

1.3 

3.3 

0.69

98.59 

.82

41.9 

14.8 

6.2 

15.6 

11.8 

2.6 

1.3 

3.3 

0.74

98.24 

.82

41.9 

14.8 

6.1 

15.7 

11.7 

2.7 

1.3 

3.2 

0.73

98.13 

.82

42.1 

15.0 

6.1 

15.6 

11.8 

2.6 

1.3 

3.3 

0.68

98.48 

.82

42.4 

14.8 

6.2 

15.6 

11.7 

2.6 

1.3 

3.2 

0.73

98.53 

.82

42.3 

14.9 

6.2 

15.6 

11.8 

2.7 

1.3 

3.3 

0.74

98.84 

.82

42.3 

14.7 

6.1 

15.6 

11.8 

2.6 

1.3 

3.2 

0.78

98.38 

.82

Amphibole structural formula — 23 oxygens

a -——.—— AlTM

MTM -———-

Allot 2

ffe11 Jt V

Mg — ---— -

Ti .. ____

Q. ______ 

_ . _ _

NTA ...

K

Papike A/R3 -

6.02 

1.98 

0.53 

2.51 

0.74 

3.34 

0.35 

0.084 

1.79 

0.75 

0.24

A

6.01 

1.99 

0.54 

2.53 

0.73 

3.34 

0.35 

0.083 

1.81 

0.72 

0.24

A

6.00 

2.00 

0.53 

2.53 

0.74 

3.34 

0.36 

0.080 

1.79 

0.75 

0.24

A

6.02 

1.98 

0.51 

2.49 

0.74 

3.37 

0.36 

0.078 

1.81 

0.74 

0.24

A

6.01 

1.99 

0.52 

2.51 

0.74 

3.34 

0.36 

0.084 

1.82 

0.72 

0.24

A

6.02 

1.98 

0.52 

2.50 

0.73 

3.36 

0.35 

0.083 

1.80 

0.75 

0.24

A

6.02 

1.98 

0.55 

2.53 

0.73 

3.32 

0.36 

0.077 

1.81 

0.72 

0.24

A

6.06 

1.94 

0.55 

2.49 

0.74 

3.32 

0.34 

0.082 

1.79 

0.72 

0.24

A

6.03 

1.97 

0.54 

2.51 

0.74 

3.32 

0.35 

0.083 

1.80 

0.75 

0.24

A

6.06 

1.94 

0.54 

2.48 

0.73 

3.33 

0.34 

0.08

1.81 

0.72 

0.24

A

'Total Fe expressed as FeO.

2 Total Al is a plotting parameter in figure 16A.

3 Analysis accepted (A) or rejected (R) by Papike and others (1969) screen for amphibole probe analyses. All "R" analyses listed were rejected on the basis of one 

are indistinguishable from "A" analyses.
22 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

Table 8. Published compositions of Black Canyon kaersutite megacrysts.

[n.d., not determined; —, not calculated]

Sample No. C/S 1 EC-2-24 2 1349243 3 1064343 HD-1' HD-2"

Analyses (weight percent oxide)

Amphibole structural formula—23 oxygens

Papike A/R7 -

HD-3"

Si02 — — — -

A12O 3 -------

FejOj——— - 

VoT\

FeO t°t 5 ......

MgO — — — -

PaO

Nap — — —

K f)

MnO — — — -

Cr203 --~

Total — - 

Mg ratio= 

Mg/(Mg+SFe)

41 46

3.32

5.70

8.69

1 1 £.9

U

£S\

2.29

1.72

5.70

0.08

n.d.

99.81 

.74

Af\ 1

143

n.d.

n.d.

8.3 

14.0

11.0 f\ S

2.0

5.7

0.1

0.1

98.4 

.75

ATI Af.

13.77

n.d.

n.d.

8.98 

13 no

2.51

1.95

n.d.

n.d.

97.85 

.72

40.55

14.59

n.d.

n.d.

8.63

11.03

2.53

1 Q(\

e -78

0.14

n.d.

99.03 

.74

40 3fi

1 A «5C

n.d.

n.d.

8.69

11 ^8

10.93

f\ A^l

9 00

5.49

n.d.

n.d.

97.96 

.74

40.1

1 A f\

n.d.

n.d.

7.9

11.4

2 5

1.9

5.7

0.14

0.19

98.33 

.76

39 5

14.1

n.d.

n.d.

9.7 

132

11.5 f\ S

1.9

5.5

0.16

0.03

98.19 

.71

40.2

14.1

n.d.

n.d.

8.3 

14.0

11.5

f\ S

1.9

5.6

0.13

0.03

98.36 

.75

Si ...._.__._

AlTM — — — -

Al^ ____

Altot6 ___

Fe11 _____

Mg ———...

Mn — — — —

Ti— — ..... ...

rv, _

Ma

K ...... ........

5.93

2.07

0.33

2.40

1.04

2.92

0.10

0.61

1 78

011

2.14

0.32

2.46

1.01

3.04

0.01 f\ f/\

0.01

1.71

0.73

0 17

5.94

2.06

0.33

2.39

1.10

2.84

—

f\ £1

1 78

0.72

O Ifi

c 87

2.13

0.36

2.49

1.04

2.96

0.02

f\ tii

1.71

0.71

n ifi

5.90

2.10

0.38

2.48

1.06

2.96

—

0.60

1.71

0.70

O 17

5 84

2.16

0.27

2.43

0.96

3.10

0.02

A £S)

0.02

1 78

0.70

o i^;

^! BO

2.18

0.26

2.44

1.19

2.90

0.02

0.61

0.00

1 81

0.74

0 Ifi

« Qf.

2.14

0.28

2.42

1.01

3.04

0.02

0.61

0.00

1 8O

0.73

o i^;

Campbell and Schenk (1950): wet-chemical analysis of kaersutite megacryst. Data are presented as anhydrous and FeOtot calculated 

for comparison with microprobe analyses. Total calculated using values for FeO and Fe^.

2Boettcher and O"Neill (1980): microprobe analysis of kaersutite megacryst.

3Garcia and others (1980): microprobe analyses of three kaersutite megacrysts.

4A.J. Irving (1982) written commun.: microprobe analyses of kaersutite megacrysts.

5Total Fe expressed as FeO.

6Total Al values for comparison with those in tables 6-7 and plotted in figure 16 A; these data are not plotted.

7 Analysis accepted (A) or rejected (R) by Papike and others (1969) screen for amphibole probe analyses. All "R" analyses listed were 

rejected on the basis of one criterion and are indistinguishable from "A" analyses.

dikes. These values are mostly higher than the highest 

TiO2 compositions found by us, either for clinopyroxene 

megacrysts or clinopyroxene in xenoliths. Roden and 

Shimizu (1989) also show high contents of strontium and 

rare earth elements (REE) in clinopyroxenes with REE 

patterns that are variably enriched or depleted in light rare 

earth elements (LREE) compared to heavy rare earth elements (HREE).

All clinopyroxenes in table 4 have compositions characteristic of high-pressure origin, notably high values of 

Ca-Tschermak's molecule: 15 to 19 percent in diopsides, 

13 to 24 percent in poikilitic grains of wehrlite, and 16 to

27 percent in megacrysts. The poikilitic clinopyroxenes 

have compositions intermediate between Cr-diopside and 

augite megacrysts (table 4).

Orthopyroxene compositions show less variation (table 5; fig. 15) than clinopyroxene. Orthopyroxene grains 

intergrown with kaersutite in the vein of Iherzolite xenolith BC-2-21 are slightly richer in Fe and poorer in Cr 

than grains from other Iherzolite xenoliths. TiC>2 contents 

of orthopyroxenes in the three Iherzolite samples (table 5) 

range from 0.08 to 0.37 percent, and Orthopyroxene in the 

vein of sample BC-2-21 (table 5) has a TiO2 content within this range (0.17 percent).
COMPOSITION OF DIKES AND INCLUSIONS 

Table 9. Compositions of phlogopite and olivine.

[n.d., not determined]

23

Phlogopite grains (P) intergrown with kaersustite and apatite in kaersutite-phlogopite-apatite cluster 

(KPA)

Sample No. KPA-P1 KPA-P2 KPA-P3 KPA-P4 KPA-P5 KPA-P6 KPA-P7

Olivine 

megacryst 

(OM)

OM

Analyses (weight percent oxide)

SiQ2 — — — -

AljQs ———

13ff)KXl

MgO -— -— -

PaO _

Na2O — — — -

V f~\

m^ ..... ..

MnO — -— —

<~v r\

NiO — — — -

p

Total — — 

Mg ratio= 

Mg/(Mg+SFe)

Na2O/K2O— -

Structural 

formulae

S .—.——_.

A1tOt3.

Fe11 — — — —

\Xa IVlg ............. -————----

Mn-—— ------ 

j^j ______

Ti

Cr— ----- — —

Ca

J^a _______ 

J£ ________

F— — — -— -

35.3 

15.7 

16.3 

11.4 

0.15 

0.78 

8.6 

9.8 

0.15 

0.031 

n.d. 

0.004

98.22 

.56 

.089

5.2 

2.7 

2.0 

2.5 

0.02 

n.d. 

1.1 

0.004 

0.02 

0.22 

1.6 

0.001

35.1 

15.8 

16.3 

11.4 

0.15 

0.82 

8.7 

9.7 

0.14 

0.031 

n.d. 

0.000

98.14 

.56 

.094

5.2 

2.7 

2.0 

2.5 

0.02 

n.d. 

1.1 

0.004 

0.02 

0.23 

1.6 

0.000

35.3 

15.6 

16.3 

11.4 

0.14 

0.77 

8.6 

9.7 

0.14 

0.033 

n.d. 

0.001

97.98 

.56 

.090

5.2 

2.7 

2.0 

2.5 

0.02 

n.d. 

1.1 

0.004 

0.02 

0.22 

1.6 

0.000

35.1 

15.8 

16.5 

11.4 

0.14 

0.77 

8.7 

9.8 

0.14 

0.025 

n.d. 

0.001

98.38 

.55 

.088

22 oxygens

5.1 

2.7 

2.0 

2.5 

0.02 

n.d. 

1.1 

0.003 

0.02 

0.22 

1.6 

0.000

35.0 

15.8 

16.4 

11.3 

0.16 

0.77 

8.7 

9.8 

0.14 

0.032 

n.d. 

0.001

98.10 

.55 

.088

5.1 

2.7 

2.0 

2.5 

0.02 

n.d. 

1.1 

0.004 

0.02 

0.22 

1.6 

0.000

35.0 

15.6 

16.3 

11.3 

0.15 

0.76 

8.6 

9.8 

0.14 

0.026 

n.d. 

0.001

97.68 

.55 

.088

5.2 

2.7 

2.0 

2.5 

0.02 

n.d. 

1.1 

0.003 

0.02 

0.22 

1.6 

0.000

35.0 

15.6 

16.2 

11.3 

0.13 

0.76 

8.6 

9.9 

0.13 

0.030 

n.d. 

0.002

97.65 

.55 

.088

5.2 

2.7 

2.0 

2.5 

0.02 

n.d. 

1.1 

0.003 

0.02 

0.22 

1.6 

0.001

38.9 

n.d. 

19.4 

41.5 

0.32 

n.d. 

n.d. 

n.d. 

0.24 

n.d. 

0.12 

n.d.

100.48 

2R>79 

n.d.

4 oxygens

1.0 

n.d.

0.42 

1.6 

0.005 

0.002 

n.d. 

n.d. 

0.008 

n.d. 

n.d. 

n.d.

'Total Fe expressed as FeO. 

2Fo=Mg ratio x 100. 

3Total aluminum ions.

M.F. Roden (written commun., 1992) has found a 

much smaller range of TiO2 (0.06 to 0.21 percent) and 

A12O3 values for orthopyroxene grains in analyses of 

Black Canyon xenoliths than we report (we found 3.2 to 

5.0 percent A12O3 in the three samples, whereas Roden 

found 4.4 to 5.6 percent A12O3). We also found higher values of MgO (as much as 33.4 percent, compared to 32.8 

found by Roden). For other oxides, Roden's orthopyroxene 

data have larger ranges that completely overlap the values 

reported in table 5. However, compared to either set of 

xenolith data, orthopyroxene grains in the kaersutite vein 

of xenolith BC-2-21 are higher in FeO (7.0 percent).

AMPHIBOLE

We analyzed 76 amphibole samples from xenoliths and 

megacrysts (table 6) with an electron microprobe. To avoid 

bias in favor of large or small grains or of position relative to 

the dike walls, hand samples were taken at measured intervals from exposures X, Y, and Z (location 13). Whole or parts 

of 58 megacrysts were selected randomly from these samples 

for the analyses. In polished thin sections made from samples 

of zones 3, 4, and 5, all mafic mineral grains were traversed 

with the electron beam to test the possibility of compositional 

zoning. All analyzed amphiboles were homogeneous.
24 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

Interstitial amphiboles in peridotite xenoliths (table 7) 

are pargasite (low Ti-values and high Mg ratios). All other 

amphibole samples from xenoliths, including those in the 

KPA cluster (fig. 16A and B\ table 6), are kaersutite (definition of Leake, 1978) with at least 0.5 Ti atoms per formula unit. Black Canyon amphibole megacrysts form a 

chemically coherent group (figs. 16A through C). Compositions from samples of apparently euhedral megacrysts 

and those of matrix-size grains in thin sections (AM7,

0.6

0.4

02

6.0 

5.0 

4.0 

3.0

|

2.0

1.0 

0.8 

0.6 

0.4 

0.2 

0

2.2 2.4 2.6 

TOTAL Al ATOMS

2.8

B

CD

0.6 0.7 0.8 

Mg-RATKD

0.9

12.5 13.0 13.5 14.0 14.5 15.0 

A12O3 (WEIGHT PERCENT)

15.5

Figure 16. Amphibole compositional variations. A, plot of structural Al and Ti (after Best, 1974, 1975). B, Mg-ratio and TiO2. C, 

variations of Cr2O3 and A12O3. Symbols: inverted triangle, 

megacrysts, including supposedly euhedral grains and matrixsized grains; circle with x, fused grain (altered megacryst); filled 

diamond, kaersutite in wehrlitic xenoliths; large open circle, 

kaersutite in kaersutite-phlogopite-apatite (KPA) aggregate; small 

filled dot, vein; upright triangle, Iherzolite xenoliths.

table 6) are well within the compositional range of plotted 

parameters for all amphibole megacrysts.

Similar data plotted by Best (1974) show that amphibole megacryst compositions worldwide have Ti values of 

0.3 to 0.7 atoms per formula unit and Al values from 1.9 

to 2.8 atoms per formula unit (fig. 16A). Compositions of 

megacrysts from Grand Canyon localities alone occupy 

nearly the entire range of amphibole megacryst 11 values 

(Best, 1974). By comparison, all but three Black Canyon 

kaersutite analyses fall into a restricted compositional 

range: Ti from 0.61 to 0.67 and Al from 2.4 to 2.6 atoms 

per formula unit (fig. 16A). Kaersutite grains from the vein 

of xenolith BC-2-21 (table 6; small dots, fig. 16A through 

C) have compositions indistinguishable from most amphibole megacrysts.

Figure 16B displays Mg ratio plotted against TiO2 

content (as weight percent) for all analyzed Black Canyon 

amphibole samples. Of the 61 megacryst compositions 

plotted, most are anhedral grains or cleavage fragments; 

however, three were selected because they appeared to be 

euhedral (table 6; fig. 165). All megacryst samples but one 

have Mg ratios between 0.64 and 0.76. TiO2 values for 

most megacrysts are bracketed between 5.5 and 6.0, although analyses of Black Canyon megacrysts from the literature range to as much as 6.3 TiO2 (table 8).

Three megacryst samples plotted in figure \6B have 

TiO2 values much lower than the dominant range (4.8 to 

5.0) and markedly high contents of Fe. Two of these low-Ti 

megacrysts (circle with x, figs. 16A through C) are parts of a 

single fused grain; thus, the Mg ratios of 0.67 and 0.68, and 

TiO2 values of about 4.0 weight percent probably represent 

compositions that were altered by reaction in the magma. 

The other megacryst with low contents of Ti and Mg is from 

the contact zone; it has very high A12O3 m& a^so may nave 

undergone partial melting, dissolution, or reaction.

Amphibole grains intergrown with phlogopite and apatite (KPA, table 6; large open circles, figs. 16A through 

C) have Ti values and contents of A12C>3 and Cr2C>3 similar to megacrysts, but are distinguished by markedly low 

Mg ratios (0.55 to 0.56) compared to megacrysts. Therefore, the KPA grains do not resemble interstitial pargasite 

from Iherzolite xenoliths (filled diamonds, figure 16A 

through C), which have high Cr2C>3 and A12C>3 relative to 

megacrysts.

Megacrysts vary more widely than other amphiboles 

in A12O3 content (14.3 to 15.7; fig. 16C), at low values of 

Cr2O3 (0.20 to less than 0.01). The alumina contents of 

poikilitic amphibole in wehrlitic xenoliths are lower and 

more restricted than megacrysts, but the Cr2C>3 values vary 

from slightly higher than megacrysts (0.23) to ones higher 

than Iherzolite amphiboles (0.99).

Figure 17 shows the compositions of amphibole megacrysts plotted against position in the dike segment at location 13 (table 1). The average compositions of three 

anhedral and two euhedral kaersutite grains from other
DISCUSSION 25

dikes of the swarm are included for comparison. The 

megacrysts are essentially uniform in Al and Cr across the 

zones of the dike, and all other compositional variations 

show no correlation with position in the dike.

One small amphibole grain in the contact zone is 

markedly different from the bulk of megacrysts in Al and 

Ti values and Mg ratio. However, other zones contain amphiboles with similar low Mg ratios—all these grains are 

fused and probably were altered by reaction with the magma, as discussed above. Other than this grain, Ti- and Alvalues show little variation across the width of the dike. 

Chrome contents and Mg ratios vary most widely in zones 

3 and 4, probably owing to the larger number of analyzed 

grains, which reflects the greater abundance of grains in 

these zones (fig. 135).

Basu (1978) determined K, Rb, Sr, and Ba contents 

and Sr-isotopic ratios for a Black Canyon kaersutite megacryst and part of the surrounding dike matrix. The potassium content determined by Basu (1978) (1.6 weight 

percent K^O) is within the range of microprobe determinations in our study (range 1.3 to 2.0 weight percent K2O) 

for megacrystal and xenolithic kaersutites. A kaersutite 

megacryst from Black Canyon analyzed by Irving and 

Frey (1984) is relatively enriched in LREE compared to 

HREE and has a chondrite-normalized LREE/HREE value

East

Figure 17. Variations of amphibole (kaersutite) compositions plotted against distance across the width of the dike at location 13 for 

exposures X, Y, Z; compared to amphibole megacrysts from other 

Black Canyon dikes and grains that appeared euhedral. Symbols: 

inverted triangles, kaersutite megacrysts from location 13; 

squares, megacrysts from other dikes; circles, euhedral grains. 

Abscissa location of symbols for other dikes is not significant.

of about 3.0. Sr-isotopic ratios for two Black Canyon 

kaersutite megacrysts are 0.70275±0.00005 (Basu, 1978) 

and 0.70273 (Poland and others, 1980). These values from 

different laboratories are in remarkable agreement and are 

comparable to the ratios of mantle-derived kaersutites 

worldwide (Basu, 1978). An amphibole analyzed by Daley 

and DePaolo (1992) has a ENd value of +6.4 and Sr-isotopic ratio of 0.70293, which is slightly higher than those of 

the megacrysts analyzed by Basu (1978) and Poland and 

others (1980), but much lower than values for dike matrix.

OTHER MINERALS

Seven analyzed phlogopite flakes (table 9) in the KPA 

cluster (table 6) have constant TiO2 contents of 9.8 weight 

percent and Mg ratios between 0.39 and 0.55. Thus, all the 

mica compositions lie within the range reported by Irving 

(1977) and are similar to those from secondary phlogopites in peridotites (Boettcher and O'Neil, 1980). Although 

we did not analyze feldspars, some may be of high-pressure origin; for example, Irving (1977) analyzed titanomagnetite and sodic plagioclase (oligoclase-andesine) 

megacrysts from the dike segment at location 13. Poland 

and others (1980) reported anorthoclase megacrysts that 

have a range of 87Sr/86Sr between 0.70298 and 0.70396. 

The higher isotopic ratio of strontium is similar to that determined by Poland (1980) for Black Canyon dike matrix 

(see above); thus, the anorthoclase could have crystallized 

from the dike magma under high pressure conditions.

DISCUSSION

FORMATION OF THE BLACK CANYON 

VENT ARE A

Geologic and magnetic mapping indicate that an eruptive center formed at the south end of the Black Canyon 

dike arrays. Lava flows are absent or are of relatively 

small volume in the vent area; also, fragments of scoriaceous basalt are rare, and no cinder horizons are interbedded either in fanglomerate or tuff breccia. These 

observations imply that the volume of magma was too 

small or conduit pressures were too low to sustain lava 

fountaining.

Many lines of evidence, such as the mixtures of fanglomerate and rapidly chilled, fragmented magma in the 

tuff breccia, accretionary lapilli in layered tuff breccia, and 

pepe"rite zones in the tuff breccia adjacent to some dikes 

indicate a wet depositional environment. Therefore, the 

tuff breccia may be the product of one or more 

phreatomagmatic eruptions, caused by basaltic magma intrusions into a relatively watery part of the fanglomerate 

deposit. However, no maar-bed deposits are preserved in
26 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

the vent area; therefore, the eruptions were not especially 

violent.

The tuff breccia, fanglomerate, and tuff-fanglomerate 

contacts are intruded by dikes and sills; thus, intrusion continued after eruption of the tuff breccia, emplacing multiple 

intrusions or a large intrusive mass that our magnetic survey indicates must be present at depth. Our field observations show that several distinct dikes with a range of 

magnetic susceptibilities crop out at the surface; therefore, 

we conclude that the magnetic source in the vent area consists of many intrusions with variable magnetizations.

Multiple injections of alkalic magma into a small area of 

venting characterize the process of diatreme formation 

(Dawson, 1967). Diatremes are very deeply rooted structures with complex internal relations produced by violent 

eruptions, which are driven by high pressures from deep 

crustal or upper mantle levels. In the Black Canyon vent 

area, features such as accretionary lapilli in layered tuff 

breccia and the steep contacts between eruptive-intrusive 

units and the country rock in the southern part of the area 

support a possible origin of the vent area as a protodiatreme.

The composition of the dikes and the presence of 

mantle xenoliths support derivation of the dike magmas 

from the mantle, but no features of deposits or their contacts at the Black Canyon vent area indicate that eruptions 

were driven by the extremely high pressure of a deep-seated source. Instead, as noted above, we see evidence for a 

relatively few phreatomagmatic eruptions in the vent area. 

If the dikes were injected directly from mantle levels, 

some deficiency—either of magma volume or pressure, or 

both—limited intrusive and eruptive events. We conclude 

that the vent area formed from explosive interaction between intrusive magma and water-bearing sediments near 

the surface. The abundance of volatiles in the host rock 

may have localized or even initiated eruptive activity.

STRUCTURES AND INTRUSIVE PROCESS OF THE 

DIKE ARRAYS

North of the vent area, the localized magnetic expressions of the dikes indicate that they are not underlain by 

larger magmatic masses. No eruptive deposits crop out in 

association with the dike arrays, nor have we seen any deposits interbedded in fanglomerate. The marked relief of 

dike exposures in washes, gaps in outcrops of continuous 

dike segments on ridge tops, the common presence of fanglomerate wall-rock inclusions and of vertical joints related to an upper cooling surface suggest that the present 

erosional surface is close to the upper contacts of the dike 

segments.

The northeastern dike at Shiprock, New Mexico, studied in detail by Delaney and Pollard (1981), provides a 

good model for interpreting the outcrop pattern of Black 

Canyon dike segments. Deflection of dike tips between

offset segments and bulbous swellings are observed at 

both localities. Delaney and Pollard (1981) showed that tip 

deflections are produced by mutually interfering stress 

fields localized around the intrusive tips. These stress 

fields interact because the dike segments were all intruded 

virtually simultaneously and do not each represent discrete, independent conduits connected to a magma source 

in the deep crust or upper mantle.

In the idealized dike depicted by Delaney and Pollard 

(1981; fig. 5), each segment is a sheetlike extension that 

merges downward into a main dike. The main dike grows 

by sending out these smaller extensions (or "fingers"— 

Baer and Reches, 1987) into the country rocks above or 

ahead of the main magma conduit. If the pressure and supply of magma are maintained, the magma extensions may 

coalesce by dilation of the country rocks, and this causes 

the conduit to grow laterally and upward (Delaney and 

Pollard, 1981). If the uppermost extensions never coalesce, the cooled dike consists of a main tabular sheet of 

crystallized magma with subordinate sheets projecting 

from many sites (fig. 5).

Like the bulbous swellings of the Black Canyon dikes, 

"buds" (Delaney and Pollard, 1981) at Shiprock are located at sites where brecciated country rock is seen in the 

dike. According to Delaney and Pollard (1981), the dike 

formed buds by abrasion erosion and brecciation of wall 

rocks during intrusion, a process that allowed the magma 

conduit to increase in width. Delaney and Pollard (1980) 

also suggested that plugs related to the northeastern 

Shiprock dike probably originated as bulbous swellings or 

buds, which enlarged enough to become volcanic vents. 

Buds also might be sites of dike branching (Delaney and 

Pollard, 1981).

Using the model of Delaney and Pollard (1981), the 

Black Canyon dikes probably constitute as few as three 

different intrusive sheets. Dike segments between locations 

1 and 6 (fig. 1) are related to a main northeastern dike, 

segments between locations 7 and 1 IB are upper parts of a 

northwestern dike, and segments at locations 12 and 13 and 

south of Highway 93 are all extensions from the third dike.

Other than in the vent area discussed above, the Black 

Canyon dikes have no observable branches or vents, probably because all exposures are so close to the preerosional 

surface. Bulbous swellings clearly formed from the incorporation of easily eroded fanglomerate masses by dike 

magma (fig. 14). With only one exception, all internal 

chilled zones are adjacent to pods of incorporated fanglomerate. If bulbous swellings initiate plugs, which are 

eruptive vents, as concluded by Delaney and Pollard 

(1981), the evidence of that relation remains unexposed 

beneath the vent area. Although the magnetic anomaly 

over the vent area could be caused by a plug, we prefer to 

interpret the source of the anomaly as many smaller intrusions of variable magnetization, because this relation is 

observed in outcrops.
DISCUSSION 27

Our study found no definitive evidence of the likely 

sequence of intrusive and eruptive events. Campbell and 

Schenk (1950) suggested that the Black Canyon vent area 

formed after injection of the dike swarm, but the evidence 

does not preclude the possibility that intrusions and phreatic eruptions formed the vent area first, after which intrusion shifted to the north.

Measurement of directional indicators of dike propagation is limited by the degree of exposure (Delaney and 

Pollard, 1981). Features such as "cusps" (fig. 5; Delaney 

and Pollard, 1981), or grooves in wallrock at the dike contacts (Baer and Reches, 1987) may be used to determine 

propagation direction for a swarm. However, features such 

as cusps must be exposed below the level of the magmatic 

extensions to be reliable, and the wall rocks must be cohesive enough to preserve measurable striations. None of 

these requirements is fulfilled at Black Canyon.

If inclusion concentrations and the symmetrical arrangement of inclusion sizes in the Black Canyon dikes are 

due to flow sorting (see below), the longitudinal coalescence of disaggregated fanglomerate into the conduit axis 

of the dike segment at location 3 can be interpreted to support a south to north flow of magma in that dike segment. 

The limited value of this speculation is further constrained 

by the lack of exposure. Propagation directions may also be 

inferred from fanning of the dike system (Baer and Reches, 

1987), but this inference is statistically based and requires a 

larger number of exposed dike segments and arrays than we 

can find in the Black Canyon area.

ORIGIN OF THE MAFIC-ULTRAMAFIC 

INCLUSION SUITE AND HOST MAGMA

Principal features that support a deep origin for mafic 

inclusions in the Black Canyon dikes include (1) the presence of kaersutite megacrysts in association with magnesian peridotite xenoliths, including kaersutite-bearing 

types; (2) intergrowths of kaersutite and aluminous clinopyroxene; (3) the overwhelming abundance of cleavage or 

irregular anhedral shapes among the kaersutite crystals; 

and (J4) melting or fragmentation of kaersutite megacrysts 

in the host basalt. The absence of correlation between 

megacryst compositional variations and positions of the 

analyzed samples in the dike at location 13 shows further 

that crystallization differentiation did not occur in place.

The compositions of mafic megacrysts in the Black 

Canyon dikes, especially of kaersutite and associated pyroxene, are comparable with those reported for high-pressure megacryst suites worldwide (Wilshire and Trask, 

1971; Best, 1974; Irving, 1974, 1977). The association of 

kaersutite and Fe-rich aluminous pyroxene with peridotite 

and Al-augite-bearing xenoliths in the Black Canyon dikes 

and tuff breccia is common at xenolith-megacryst localities elsewhere in the world (for example, Wilshire and

Binns, 1961; Best, 1970, 1974; Irving, 1974; Wilkinson, 

1975; Wilshire and Shervais, 1975; Wass, 1979; Wilshire 

and others, 1980). The presence of this association in the 

Black Canyon suite further supports the idea of a common 

origin for the mafic megacrysts and xenoliths (Wilshire 

and Trask, 1971; Best, 1974; 1975; Irving, 1980; Wilshire 

and others, 1988).

Kaersutite and kindred high-pressure mafic minerals in 

basaltic lavas may form either from crystallization in the 

host magma at high pressure ("high-pressure phenocrysts"—Binns, 1969; Green and Hibberson, 1970; Binns 

and others, 1970; Wilkinson, 1975; Wass, 1979) or may be 

accidental inclusions from the fragmentation of polycrystalline aggregates (dikes or veins) already present in the mantle (Best, 1970; Wilshire and Trask, 1971; Irving, 1974). 

The shapes, reaction textures, and compositions of the mafic megacrysts, as well as the isotopic disequilibrium between kaersutites and dike rock at the Black Canyon 

locality (Basu, 1978; Poland and others, 1980), indicate 

that these amphiboles are not cognate to the magma and 

thus are xenocrysts.

Clinopyroxene megacrysts are of low abundance in the 

inclusion suite compared to kaersutites, and the compositional variation between clinopyroxenes of the megacryst 

suite and poikilitic grains in wehrlitic xenoliths is not as 

well delineated. Because clinopyroxene megacrysts have 

compositions that overlap the poikilitic grains in peridotite, 

they could have a common origin. Therefore, clinopyroxene megacrysts might be either xenocrysts or high-pressure 

phenocrysts.

Campbell and Schenk (1950) classified the dikes as 

camptonite because they assumed that the large kaersutite 

grains crystallized in place. According to S0renson (1974), 

camptonite is an intrusive alkali gabbro containing cognate 

sodic amphiboles, titanaugite, and biotite±olivine. However, the Black Canyon dikes do not fit these criteria because 

the amphiboles are neither sodic nor cognate. We prefer to 

classify the dikes by the compositions of matrix and the 

main matrix minerals, Ti-augite and olivine. These minerals, the norms of unleached rocks, and the isotopic composition of matrix samples are all characteristic of alkali 

olivine basalt. Therefore, alkali olivine basalt probably is 

the best petrologic designation for the dike rocks.

Mantle xenoliths of the inclusion suite, as well as the 

isotopic composition of the matrix (Basu, 1978; Poland and 

others, 1980) indicate a mantle origin for the Black Canyon 

alkali olivine basalt magma. Numerous studies (for example, Prey and Green, 1974; Hutchison and others, 1975; 

Wass and others, 1980; Boettcher and O'Neil, 1980) have 

shown that alkali basalts cannot be produced by the melting 

of anhydrous peridotites with compositions similar to the 

most common xenolith types in suites from either kimberlite or basalt. At least one precursory event must add the 

incompatible elements—such as Na, K, and Ti and minor 

elements such as U, Th, and LREE—to parental mantle
28 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

peridotite in order for it to produce basaltic magma from 

partial melting.

Geochemical studies of xenoliths show that magnesian 

mantle peridotites can become enriched in incompatible 

trace elements by metasomatism and remain relatively refractory in major-element composition (for example, 

Kempton, 1987; McDonough and Frey, 1989). Composite 

xenoliths of peridotite in contact with kaersutite- or biotiterich rocks, Al-augite pyroxenite, and hybrids of these lithologic types have been shown to be mafic intrusions in peridotite (Wilshire and Shervais, 1975; Irving, 1980; Wilshire 

and others, 1980; Menzies and others, 1985; Nielson and 

others, 1993). These intrusions represent mantle magmas 

that locally metasomatized peridotite wall rock, enriching it 

in incompatible elements, before generation of the xenolith 

host basalt. Xenolith-megacryst suites, including composite 

xenoliths and megacrysts with compositions similar to 

those of minerals in mantle intrusions, are found (1) in 

Arizona at the north rim of the Grand Canyon (Best, 1974, 

1975) and in the San Carlos and Four Corners areas 

(Wilshire and others, 1988), (2) in New Mexico at Kilbourne Hole (Wilshire, Schwarzman, and Trask, 1971; Irving, 1980; Roden and others, 1988), and (3) in California at 

Dish Hill, Deadman Lake (Wilshire and Trask, 1971; 

Wilshire and others, 1980; Nielson and others, 1993), and 

the Cima volcanic field (Wilshire and others, 1991).

Although the most abundant high-pressure inclusions 

in the Black Canyon dikes are amphibole xenocrysts and 

relatively minor peridotite xenoliths, the origin of megacrysts from a source within mantle peridotite is shown by

(1) olivine-rich xenoliths that contain interstitial amphibole,

(2) a composite sample with a thin kaersutite vein, and (3) 

reports of amphibole-bearing pyroxenites (AJ. Irving, written commun., 1983). Clinopyroxene compositions from 

Group I Black Canyon xenoliths have widely variable contents of incompatible elements, including the LREE (Roden 

and Shimizu, 1989). Such wide variations can occur in regions where LREE-enriched magma intruded and locally 

metasomatized refractory peridotite (Wass and others, 

1980; Reisberg and Zindler, 1986; O'Reilly and Griffin, 

1988; Nielson and others, 1993). The kaersutite xenocryst 

analyzed by Irving and Frey (1984) is relatively enriched in 

LREE and could represent a metasomatizing melt. Therefore, the mafic-ultramafic suite of inclusions in Black Canyon dikes could be derived from a mantle source analogous 

to ones rich in pyroxenite xenoliths, such as Lunar Crater, 

Nevada (Bergman and others, 1981).

We conclude that the physical and chemical evidence 

strongly suggests that the xenocryst-xenolith suite in Black 

Canyon dikes probably came from a region of peridotite 

that had been invaded locally by a large volume of hydrous 

alkali basalt magma. The magma crystallized to form a 

dense complex of kaersutite-rich pyroxenites and hornblendite dikes and veins (O'Reilly and Griffin, 1988; Griffin 

and others, 1988; Nielson and others, 1993). Similar to outcrops of hornblendite rock types in the peridotite massif at 

Lherz, France (Conque're', 1970). Coarse-grained dikes 

probably were broken up by the later dike magma, thus 

producing the large kaersutite xenocrysts that are found in 

the Black Canyon dikes.

ORIGIN OF ZONING AND INCLUSION 

DISTRIBUTION PATTERNS

ZONING

Our observations of all the dikes in Black Canyon arrays show that the "zoning" described by Campbell and 

Schenk (1950) is a rare combination of features that are all 

present coincidentally in the dike segment at location 13 

and are all oriented parallel or nearly parallel to the longitudinal contacts and axial planes of dikes. These features 

include alternating fissile and massive matrix-structure 

zones that change in position and symmetry along strike, 

elongation of tabular vesicles, and preferred orientation of 

tabular matrix grains and inclusions. Flow banding (fig. 

10), chilled internal zones, and incorporated fanglomerate 

masses are the only notable internal features of the Black 

Canyon dikes that are not seen in the exposures at location 

13. The dike segment at location 13 also contains abundant inclusions (including rare clasts from the fanglomerate) that are concentrated in the dike axial zone and are 

sorted symmetrically, by size, about the axis.

We believe that the alternations of matrix fissility and 

the alignments of tabular vesicles and xenocrysts are the 

preserved patterns of magma flow during intrusion. Platy 

or elongate rock fragments, bubbles, and crystals being 

carried in the magma were oriented within the longitudinal 

flow planes. The constant matrix grain size across the dike 

segment at location 13 suggests that all internal zones 

cooled at the same rate after the magma had stagnated. 

Shear planes present in the last stage of intrusion became 

flow banding or longitudinal joint planes as the rate of 

flow decreased and cooling began.

Three or more symmetrical, regularly alternating 

zones are rarely observed in the Black Canyon dikes; 

these zones probably represent stable laminar-flow regimes 

that persisted only locally within individual dike segments. 

Enlargement of the magma conduit by erosion of fanglomerate wall rock promoted development of turbulent-flow 

vortices. Bulbous swellings grew at the sites of erosion. 

When the vortices cooled, they were preserved as curved 

joint planes.

INCLUSION CONCENTRATIONS AND SIZE SORTING

Campbell and Schenk's (1950) hypothesis and other 

similar hypotheses about the origin of the supposed zoning 

in the dike segment at location 13 are all based on the
DISCUSSION 29

distribution and size sorting of inclusions. The interpretation of Campbell and Schenk (1950) that the kaersutites 

crystallized in place is clearly refuted by the compositional data summarized above. An alternative idea is that the 

zones at location 13 formed from multiple injections of 

magma into established dike conduits (FJ. Spera, written 

commun., 1984), but this hypothesis is not substantiated 

by the structural and textural relations we recorded in all 

other Black Canyon dike segments.

Black Canyon dike segments contain axial inclusion 

concentrations only where inclusions are abundant. Segments with relatively few inclusions show no particular 

distribution of particles or particle sizes with respect to 

structural zones. All exposed dike tips and most chilled 

margins are relatively barren of inclusions. The original 

dike crests are either eroded or unexposed, but they probably were wedge shaped, like dike tips. At location 13, 

kaersutite grains are the most numerous inclusions, but the 

three other segments with axial inclusion concentrations 

have populations in which fanglomerate clasts predominate. These relations, as well as Delaney and Pollard's 

(1981) study of the northeastern Shiprock dike, lead us to 

conclude that masses of fanglomerate country rocks were 

eroded by the intruding magma and incorporated into the 

Black Canyon dikes through the large surface area at the 

vertical dike/fanglomerate contact walls. To form axial 

concentrations, fanglomerate inclusions must have traversed the relatively barren dike margins after the masses 

became disaggregated.

Bulbous swellings formed at the sites of fanglomerate 

erosion and incorporation. The common presence of fanglomerate masses in tabular dike segments near bulbous 

swellings, such as at locations 2 and 11A (figs. 1, 6A, B), 

show that incorporated clasts may be swept from the enlarging magma conduit into an adjacent tabular dike segment. Regularly alternating matrix structure zones are 

observed in three tabular dike segments that contain a 

large volume of inclusions (tables 1, 2). Measurements at 

location 13 show that the smallest particle sizes are 

present in all zones internal to the dike contacts, whereas 

the size of the largest inclusions increases from the dike 

contacts to the axis, forming a log-normal distribution. 

This particle distribution implies a stable configuration of 

the flow regime in this dike segment. The regular alternation of fissility suggests further that the flow regime was 

laminar. We speculate that large volumes of inclusions 

may produce, or help stabilize, local laminar-flow regimes.

Size-sorted inclusion concentrations (the "zoning" described by Campbell and Schenk, 1950) also occur only in 

dike segments with abundant inclusions (table 2). At location 13, both near-surface fanglomerate clasts and kaersutite xenocrysts from the mantle were concentrated in the 

axial zones, and the largest inclusion sizes are found in the 

innermost axial zone. Therefore, whether or not the dikes 

represent multiple injections of magma, the process that

concentrated and sorted the inclusions must be related to a 

mechanical process in the magma conduits and not to 

melting or extraction of magma in the mantle. We conclude that the characteristics of the axial concentrations 

and size sorting of inclusions in the Black Canyon dikes 

resemble flow-sorting phenomena.

Evidence for efficient flow-sorting processes in the 

Black Canyon dikes is seen at location 2 (figs. 1, IB). The 

breccia at this locality probably formed when a mass of 

friable fanglomerate was incorporated into the contact 

zone at a level not far below the modern surface. At the 

present level of exposure, this partly disaggregated mass 

of wall rock, including clasts, sandy matrix, and chilled 

fragments of dike matrix, lies between the contact and 

dike axial zones. These clasts must have migrated from 

the contact zone toward the dike axis as they were carried 

both laterally and upward by the flowing magma. At location 3, fragments of partly disaggregated fanglomerate are 

found in the dike margin, but a short distance to the north 

they are concentrated into the dike axial zone. This south 

to north change from marginal incorporation to axial inclusion concentration may show that the magma in this 

dike segment was moving northward.

Flow sorting (Drever and Johnston, 1958), both of 

phenocrysts in magmatic bodies and of exotic fragments 

in brecciated intrusive bodies, is a widely reported phenomenon. For example, Baragar (1960) noted that axial 

concentrations of the largest fragment sizes characterize fibers of wood pulp in slurries. A similar phenomenon, sorting of noncognate fragments in intrusions, was reported by 

Reynolds (1954) for subvolcanic breccia at several Irish 

localities; by Wilshire (1961) for sedimentary fragments in 

a dike near Sydney, Australia; and by Wilshire, Offield, 

and Howard (1971) for coarse particles in nonfluid intrusive impact breccia at the Sierra Madera structure, Texas. 

Quasiscale-model experiments by Bhattacharji and Smith 

(1964) and Bhattacharji (1967) demonstrated that particles 

are sorted toward the axial parts of a conduit by flowing 

magmalike fluids.

Concentrations of olivine in the centers of basaltic 

dikes and slightly below the central zones of sills were 

ascribed to flow sorting by Bowen (1928, p. 145), Drever 

and Johnston (1958, 1967), Baragar (1960), Simkin 

(1967), and Gibb (1968). B6bien and Gagny (1979) reported that all phenocryst species (olivine+pyroxene+plagioclase) and even early formed matrix minerals are sorted 

into the central zones of dikes at a Greek ophiolite complex. These examples show that sorting is a common process in flowing magmas. However, current models for 

phenocryst concentration tend to favor accretionary crystallization, rather than flow sorting or flow differentiation, 

because accretion models allow the dike to be interpreted 

as a time profile (Flatten and Watterson, 1987).

Komar (1972, 1976) attributed the inward migration of 

particles in natural conduits to grain-dispersive pressures.
30 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

He also demonstrated that such pressures are larger than 

those related either to velocity gradients in the host fluid, to 

wall effects, or Magnus-type forces. Grain-dispersive pressure is due to grain-fluid or grain-grain interactions, depending on the parameters of the system. These pressures 

become important when a fluid contains more than 8 percent particles (Komar, 1972). The effect of dispersive pressures may also depend upon particle size. These 

characteristics fit our observation that axial inclusion concentrations and size sorting are only seen where inclusions 

are abundant (greater than 10 percent) and where axial and 

near axial concentrations contain inclusion sizes of at least 

20 mm (table 2).

Axial concentrations of mantle xenocrysts may be produced by sorting pressure anywhere between the mantle 

source region and the present erosional surface, but the 

concentrations of fanglomerate inclusions in Black Canyon 

dikes must form between the depositional base of the fanglomerate and the surface. This distance is unknown for the 

Black Canyon area, but the fanglomerate unit is as much as 

several hundred meters thick elsewhere (I. Lucchitta, oral 

commun., 1992). Therefore, long distances of vertical flow 

are not required to produce size sorting of abundant inclusions with an appropriate range of grain size.

Delaney and Pollard's (1981) model of dike growth implies that the sorting in Black Canyon dikes may take place 

over an even shorter vertical distance, depending upon the 

level at which individual dike segments formed as offshoots from the main dike. If the segments connect with the 

main dike above the base of fanglomerate deposits, this 

would imply that sorting processes are extremely efficient.

SUMMARY

The Black Canyon dikes are alkali olivine basalt intrusions and related ejecta; the content of mafic and ultramafic inclusions indicates derivation of the dike magma from 

the mantle. Substantial textural and isotopic disequilibrium 

between the host dike matrix and kaersutite megacrysts 

shows that the amphiboles could not have crystallized 

from the host magma, either in the crust or upper mantle, 

and thus are xenocrysts.

Identification of the kaersutite+clinopyroxene inclusions as xenocrysts requires reinterpreting the petrologic 

classification and petrogenesis of the Black Canyon dikes. 

Kaersutite grains that accompany orthopyroxene in a vein 

in a Iherzolite xenolith have compositions identical to the 

bulk of the xenocrysts, and amphiboles with variable magnesian compositions are found as interstitial grains in altered wehrlitic xenoliths. Thus, the mafic-ultramafic 

inclusion suite may represent a mantle region of peridotite 

that was intruded and metasomatized by hydrous basaltic 

magmas some time before the generation of melts that 

formed the Black Canyon dikes. The mafic megacrysts

were coarse veins and dikes that crystallized in this older 

magmatic episode. Most feldspathic and silicic minerals 

and lithic inclusions in the dikes apparently come from 

fanglomerate host rocks of the dike swarm, although anorthoclase and some plagioclase grains probably derive from 

deep crustal levels.

Zoning in the Black Canyon dikes is commonly defined by irregular and, less commonly, regular alternations 

of massive and fissile matrix structure that resemble flow 

patterns in streams. These zones are joint patterns inherited from shear planes and boundaries between magmatic 

flow regimes in the dike conduits. The joints and other 

features related to flow generally are parallel to the axial 

plane of the dike and may occur individually or in combination. The more regular symmetrical or asymmetrical textural zones are rare, and they probably represent local 

stable-flow regimes that formed and persisted over very 

short distances.

The rare axial concentration and size sorting of inclusions affects both mantle- and near-surface-derived inclusions from Miocene and Pliocene fanglomerate wall rocks 

in the best exposed dike (location 13; fig. 1) and other 

Black Canyon dikes. The log-normal distribution of the 

largest inclusion sizes in the dike segment at location 13 

indicates that mantle- and crustal-derived fragments were 

carried in a stable laminar-flow regime. Most inclusion concentration filaments are parallel to other flow-generated 

structures; the filaments are present only where inclusions 

are abundant and where maximum particle sizes reach 20 

mm or greater and, except at location 13, the most common 

inclusions are fanglomerate clasts. Thus, the most likely 

origin for the size distributions and concentration of inclusions is from flow sorting of particles in magma in the dike 

conduit and is unrelated to deep-seated magmatic processes 

or repeated injections of magma into near-surface conduits.

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Table 4. Compositions of clinopyroxene.

[Analyses by electron microprobe, J.E. Nielson, U.S. Geological Survey, analyst. Determined on ARL model SEMQ, with 3 scanning and 6 fixed spectrometers; 15 kV acceleratin

count times 50-100 s. On-peak backgrounds; analyses monitored by internal standards. All grains examined for homogeneity; each analysis represents at least 5 analyzed spots per 

are average compositions of several grains. Data reduced using modified Bence-Albee corrections]

Matrix clinopyroxene (MC)

Sample No. Z4-MC1 Z4-MC2 Z4-MC4 Y1-CM1 Y1-CM2 Y2-CM1 Y3-CM1

Clinopyroxene megacrysts (CM)

Y3-CM2 Y3-CM3 Y5-CM1 Y5-CM2 Y

Analyses (weight percent oxide)

A12O3 ——— 5.7

peQtot 2 ___ 7 I

MgO - ———— 12.5

Na->O -— - 0 46

TJQ ___ _ 34

MnO3 ——— 0.16

rV_.O -.-.... O (\f\

Total —— - 99.68 

Mg ratio= 

Mg/(Mg+SFe) .76

43.8 

9.5 

7.8 

10.9 

23.1 

0.68 

4.7 

0.14 

0.02

100.64 

.71

48.6 

4.7 

7.3 

12.9 

23.1 

0.46 

3.4 

0.15 

0.02

100.63 

.76

48.1 

7.7 

6.6 

14.1 

20.6 

1.2 

1.7 

n.d. 

0.57

100.61 

.79

48.0 

7.7 

6.6 

13.7 

20.5 

1.2 

1.8 

n.d. 

0.41

99.95 

.79

48.8 

7.7 

6.6 

13.9 

20.2 

1.2 

1.7 

n.d. 

0.51

100.65 

.79

49.6 

7.2 

5.8 

14.0 

19.5 

1.1 

1.7 

0.13 

0.32

99.35 

.81

49.8 

7.2 

5.8 

13.8 

19.4 

1.1 

1.7 

0.13 

0.35

99.28 

.81

48.0 

8.0 

6.8 

13.6 

21.0 

1.2 

2.0 

n.d. 

0.41

100.93 

.78

49.2 

7.3 

5.8 

13.8 

19.8 

1.1 

1.8 

0.13 

0.31

99.24 

.81

49.6 

7.1 

5.7 

13.9 

19.6 

1.1 

1.7 

0.13 

0.35

99.18 

.81

4

1

1

9

Pyroxene structural formula

c: 1 70

yylV ____ _ 0 22

Al^- __ — - 0.039 

Fe11 ————— 0.210

\/f n ______ _ n OflS

Ti- -- — — 0.097

Q. ______ o 002

Ca _____ o 895

Na - n (YM.

En _____ jg 94 

ps ___ _ 1 1 56

Wr» 40 SO

CaTs4 — ----- 21.55 

Papike A/R5 - A

1.63 

0.37 

0.046 

0.233 

0.604 

0.004 

0.132 

0.001 

0.921 

0.049

36.44 

8.04 

55.52

18.95 

A

1.80 

0.20 

0.009 

0.061 

0.713 

0.005 

0.095 

0.001 

0.918 

0.033

39.04 

10.70 

50.26

19.69 

A

1.75 

0.25 

0.082 

0.190 

0.765 

n.d. 

0.047 

0.016 

0.804 

0.085

46.98 

3.66 

49.35

28.65 

A

1.76 

0.24 

0.095 

0.190 

0.749 

n.d. 

0.050 

0.012 

0.806 

0.085

45.68 

5.18 

49.14

27.40 

A

1.78 

0.22 

0.109 

0.192 

0.755 

n.d. 

0.047 

0.015 

0.789 

0.085

45.60 

6.75 

47.65

25.99 

A

1.83 

0.17 

0.142 

0.179 

0.769 

0.004 

0.047 

0.009 

0.770 

0.079

44.87 

10.20 

44.93

20.25 

A

1.84 

0.16 

0.150 

0.179 

0.759 

0.004 

0.047 

0.010 

0.767 

0.079

44.51 

10.50 

44.99

20.71 

R

1.74 

0.26 

0.086 

0.1% 

0.736 

n.d. 

0.055 

0.015 

0.817 

0.085

45.19 

4.64 

50.17

28.64 

A

1.82 

0.18 

0.135 

0.164 

0.760 

0.004 

0.050 

0.009 

0.784 

0.079

44.54 

9.52 

45.94

21.13 

A

1.83 

0.17 

0.142 

0.176 

0.765 

0.004 

0.047 

0.010 

0.776 

0.079

44.56 

10.26 

45.18

19.94 

A

4

1

4

1
Table 4. Compositions of clinopyroxene—Continued.

Clinopyroxenes in Iherzolite xenoliths (L-C)

Sample No. L1-C1 L1-C4 Ll-CA6 L3-C2 L3-C4 L7-C1 L7-C3 L7-C6 L7-CA6 L4-C1 L4-C2 L4-C3 L4-C4 L4-C5 

Analyses (weight percent oxide)

Si02 —- —— ~

A12O3 — — — -

FeOtot2 - —— —

\M f*f\

r*aO

NajO — — — —

Tin

MnO — — — —

Cr D

Total — — -

Mg ratio=

Mg/(Mg+SFe) -

51.2

5.9

3.2

16.1

19.7

1.0

0.32

0.10

0.96

98.48

.90

51.2

5.9

3.3

16.0

19.9

1.0

0.32

0.10

0.93

98.65

.90

51.3

6.0

3.2

16.0

19.9

1.0

0.33

0.10

1.00

98.83

.90

50.9

6.1

3.2

15.9

19.7

1.0

0.59

0.09

1.00

98.48

.90

51.4

5.9

3.2

16.1

19.7

0.97

0.57

0.09

0.99

98.92

.90

52.1

5.4

3.3

16.6

19.9

0.92

0.32

0.10

1.1

99.74

.90

52.2 52.3 52.3 51.4

5.4 5.5 5.4 4.3

3.2 3.3 3.3 4.7

16.2 16.2 16.2 15.4

100 9fl 0 100 99 9

0.92 0.93 0.92 0.66

0.31 0.32 0.32 0.69

0.10 0.10 0.10 0.11

1.1 1.1 1.1 0.46

99.33 99.75 99.54 99.92

.90 .90 .90 .85

50.6

4.4

4.6

15.6

0.64

0.63

0.10

0.50

99.37

.86

50.7

4.4

4.7

15.6

0.63

0.65

0.10

0.47

99.65

.85

51.0

4.4

4.7

15.4

0.64

0.64

0.10

0.48

99.86

.85

51.3

4.4

4.7

15.5

22.5

0.64

0.69

0.11

0.49

100.33

.85

Pyroxene structural formula

Si ...... __ ...

AjIV ________

Al^ — - -

pgD

Mg ------

Mn— — — —— -

•pj ______

Cr ———————

\^a C ——— — — ——— —

Na

En —— - —— -

Pg ______

Wo — —— ——

CaTs4 — — — -

PapikeA/R5 —

1.88

0.12

0.135

0.097

0.881

0.003

0.009

0.028

0.775

0.071

50.54

5.00

44.46

18.27

A

1.88

0.12

0.133

0.095

0.874

0.003

0.009

0.027

0.782

0.071

50.22

4.87

44.91

18.48

A

1.88

0.12

0.137

0.098

0.873

0.003

0.009

0.029

0.780

0.071

50.11

5.08

44.81

18.41

A

1.87

0.13

0.135

0.098

0.871

0.003

0.016

0.029

0.776

0.071

50.00

5.45

44.54

18.40

A

1.88

0.12

0 I'Vt

0.098

0.878

0.003

0.016

0.029

0.772

0.069

50.22

5.60

44.18

17.85

R

1.89

0.11

0.121

0.100

0.897

0.003

0.009

0.032

0.774

0.065

50.81

5.39

43.79

16.60

A

1.90 1.90 1.90 1.88

0.10 0.10 0.10 0.12

0.132 0.132 0.132 0.065

0.097 0.100 0.100 0.138

0.879 0.876 0.877 0.839

0.003 0.003 0.003 0.003

0.008 0.009 0.009 0.019

0.032 0.032 0.032 0.013

0.776 0.777 0.775 0.870

0.065 0.065 0.065 0.047

50.15 49.95 50.06 46.59

5.56 5.71 5.72 5.13

44.29 44.34 44.21 48.28

17.19 17.23 17.19 14.84

R R R A

1.86

0.14

0.048

0.132

0.853

0.003

0.017

0.015

0.877

0 04fi

47.93

2.81

49.26

17.08

A

1.86

0.14

0.046

0 134

0.851

0.003

0.018

0.014

0.879

0045

47.78

2.90

49.32

17.03

A

1.86

0.14

0.055

0.136

0.839

0.003

0.018

0.014

0.882

0045

46.92

3.79

49.29

16.25

A

1.87

0.13

0.057

0.136

0.841

0.003

0.019

0.014

0.878

0045

46.91

4.13

48.%

14.65

A
Table 4. Compositions of clinopyroxene—Continued.

Clinopyroxenes poikilitically intergrown with kaersutite in wehrlitic xenoliths (D-C)

Sample No. D1-C1 D1-C2 D1-C3 D1-C3 D4-C3 D4-C2 D4-C3 D6-C1 D6-C2 D

Analyses (weight percent oxide)

Si02 -------

A12O3 — — -

FeO tot2 - ——

MgO ————

CaQ ~ —— ~

Na2O ——— -

TiO 2 ————

MnO ————

Cr2O3 ———

Total ——

Mg ratio=

Mg/(Mg+SFe)

51.8

4.6

4.3

15.2

22.3

0.65

0.74

0.14

0.13

99.86

.86

51.7

4.6

4.2

14.8

22.4

0.78

0.72

0.13

0.13

99.46

.86

51.9

4.7

4.4

14.8

22.2

0.73

0.71

0.14

0.13

99.71

.86

51.8

4.5

4.5

14.4

22.1

0.82

0.71

0.14

0.13

99.10

.85

48.9

7.5

6.1

13.3

19.7

1.1

1.8

0.15

0.30

98.85

.79

48.8

7.4

5.9

13.5

19.4

1.1

1.6

0.15

0.52

98.37

.80

48.8

7.3

5.9

13.4

19.3

1.1

1.6

0.15

0.51

98.06

.80

47.6

8.1

6.3

12.8

19.8

1.1

2.0

0.15

0.20

98.05

.78

48.0

8.1

6.3

12.8

20.0

1.1

2.0

0.16

0.21

98.67

.78

Pyroxene structural formula

a ......„___._.

AlIV

AlVl

Fe11 ————

Mg-—— —— -

Mn —————

nri

Cr ___ ——

Ca —————

Na —— - ——

a ____ .

Fs —————

Wo ————

CaTs 4 ———

PapikeA/R5 -

1.89

0.11

0.092

0.130

0.828

0.004

0.020

0.004

0.874

0.046

45.56

6.38

48.06

13.18

A

1.90

0.10

0.097

0.127

0.810

0.004

0.020

0.004

0.881

0.056

44.92

6.21

48.88

13.77

A

1.90

0.10

0.105

0.134

0.808

0.004

0.020

0.004

0.872

0.052

44.57

7.36

48.07

13.01

A

1.91

0.09

0.107

0.139

0.792

0.004

0.020

0.004

0.874

0.059

43.88

7.70

48.42

13.07

R

1.82

0.18

0.146

0.188

0.737

0.005

0.050

0.009

0.785

0.079

43.22

10.75

46.03

21.15

A

1.82

0

1 8 

.18

0.146

0.183

0.750

0.005

0.045

0.015

0.775

0.080

44.11

10.31

45.58

21.44

A

1.83

0.17

0.149

0.185

0.747

0.005

0.045

0.015

0.774

0.080

43.81

10.82

45.37

20.89

A

1.79

0.21

0.144

0.195

0.716

0.005

0.056

0.006

0.7%

0.080

42.67

9.88

47.45

23.80

A

1.79

0.21

0.146

0.194

0.711

0.005

0.056

0.006

0.799

0.080

42.29

10.19

47.51

23.34

A

4

4

2

'Sample numbers are for the dike segment at location 13: letter in prefix designates exposure Y or Z; prefix number refers to structural zone 1-5 (see table 

2Total Fe expressed as FeO. 

3N.d., Mn not determined. 

4Content of calcium-Tschermak's molecule.

3 Analysis accepted (A) or rejected (R) by Cameron and Papike (1981) criteria. All "R" analyses listed were rejected on the basis of one criterion and are 

indistinguishable from "A" analyses. 

6 Average of several analyzed grains.
Table 5. Compositions of orthopyroxene.

Orthopyroxene in Iherzolite (L-O)

Orth

Sample No. L1-O1 L1-O2 L1-O3 L1-O4 L5-O1 L5-O2 L5-O3 L5-O4 L5-O5 L6-O5 Ol 

Analyses (weight percent oxide)

SiO2 -— — —

Al203 --~

R0totl ---

MgO — -— -

vxHbJ ———————

Na2O — ----- ~

IHJ 2 ------ ———

MnO — — -—

Cr2O3 ———

Total ——

Mgratio=

Mg/(Mg+SFe)

54.3

5.0

6.2

32.6

1.3

0.10

0.10

0.12

0.55

100.27

.90

54.3

4.9

6.3

32.5

1.3

0.10

0.10

0.13

0.55

100.18

.90

54.5

5.0

6.3

32.5

1.3

0.10

0.10

0.12

0.55

100.47

.90

53.9

4.9

6.3

32.4

1.3

0.10

0.10

0.12

0.55

99.67

.90

55.0 55.0

3.6 3.6

5.8 5.8

33.5 33.6

1.3 1.3

0.11 0.12

0.09 0.11

0.12 0.12

0.71 0.67

100.23 100.32

.91 .91

54.9

3.6

5.7

33.4

1.3

0.11

0.08

0.12

0.71

99.92

.91

54.2

4.3

5.8

33.0

1.2

0.12

0.37

0.12

0.61

99.72

.91

55.0

3.6

5.8

33.2

1.3

0.11

0.10

0.12

0.72

99.95

.91

54.8

3.2

6.2

33.1

1.2

0.08

0.23

0.13

0.65

99.59

.90

54.1

5.2

7.0

32.2

1.2

0.1

0.1

0.1

0.4

100.5

.8

Pyroxene structural formula

S

AlTM -—— ——

AlVi ..... __ .

RJI

Mg ------

Mn .............

Ti 11 --—-.......

G __

Ca **& -----

Na _______

fij ...._.....„

R ..

Wo - ——— —

(Vr<;2 VXll. S — — — TM

Papike A/R3 --

1 87

0.13

0.073

0.175

1.673

0.004

0.003

0.015

0.048

0.007

89.08

Q 40

2.52

13.43

A

1 87

0.13

0.072

0.180

1.670

0.004

0.003

0.015

0.048

0.007

87.91

9.56

2.52

13.15

A

1 QQ

0.12

0.077

0.178

1.666

0.003

0.003

0.015

0.048

0.007

87.91

Q Sfi

2.52

12.%

A

1 87

0.13

0.068

0.178

1.673

0.004

0.003

0.015

0.048

0.007

87.88

9.59

2.53

13.63

A

1 SO 1 fiO

0.11 0.11

0.037 0.034

0.161 0.161

1.716 1.719

0.003 0.003

0.002 0.003

0.019 0.018

0.048 0.048

0.007 0.008

88.89 88.92

O £. A Q £.\

2.48 2.47

11.43 11.69

A A

1 fiO

0.11

0.039

0.159

1.716

0.004

0.002

0.019

0.048

0.007

88.99

fi ^O

2.49

11.25

A

i 07

0.13

0.049

0.163

1.701

0.004

0.010

0.017

0.044

0.008

88.91

6.39

2.39

12.59

A

1.90

0.10

0.044

0.164

1.707

0.004

0.003

0.020

0.048

0.007

90.71

6.74

2.55

10.70

A

1.90

0.10

0.032

0.176

1.711

0.004

0.006

0.018

0.045

0.005

90.43

7.22

2.36

9.93

A

I

Q

0.1

0.0

0.1

1.6

0.0

0.0

0.0

0.0

0.0

89.3

a "

2.4

14.0

A

'Total Fe expressed as FeO.

2Content of calcium-Tschennak's molecule.

3 Analysis accepted (A) or rejected (R) by Cameron and Papike (1981) criteria All "R" analyses listed were rejected OB the basis of one criterion and are indistinguishable from 
Table 6. Compositions of amphibole (kaersutite).

Amphibole megacrysts from location 13 (exposures X, Y, Z-AM)'

Sample No. X1-AM1 X1-AM2 X1-AM3 X2-AM1 X2-AM2 X3-AM1 X3-AM2 X3-AM3 X4-AM1 X4-AM2 X4-AM3 X4-AM4 

Analyses (weight percent oxide)

Si02 —— —

Aljv/j ———•»-—-

FeO** 2 ——

MoO _____

CaO _____ 

K O

TiO

v,r2vJ3

Total —— 

Mgratio= 

Mg/(Mg+SFe)

37.7 

15.7 

11.7 

12.2 

12.2 

2.7 

1.3 

3.9 

0.04

97.44 

.65

38.4 

14.5 

9.8 

13.1 

11.5 

2.6 

1.9 

5.5 

0.02

97.32 

.70

37.8 

14.8 

9.4 

13.9 

12.2 

2.6 

2.0 

5.9 

0.03

98.63

.72

38.8 

14.6 

8.5 

13.9 

11.5 

2.5 

2.0 

5.6 

0.04

97.44

.74

38.1 

14.7 

9.5 

14.1 

12.2 

2.5 

2.0 

5.9 

0.04

99.04

.73

40.7 40.6 38.5 

14.7 14.5 14.6 

7.9 8.7 8.8 

13.8 13.4 13.7 

10.9 11.0 11.6 

2.3 2.3 2.5 

2.0 2.0 2.0 

5.7 5.6 5.6 

0.23 0.03 0.02

98.23 98.13 97.32 

.76 .73 .74

38.5 

14.9 

9.0 

14.1 

12.0 

2.6 

2.0 

5.8 

0.11

99.01

.74

37.8 

15.0 

8.9 

13.9 

11.9 

2.6 

2.0 

5.9 

0.12

98.12 

.74

37.9 

15.1 

9.0 

13.8 

11.7 

2.6 

2.0 

5.9 

0.12

98.12 

.73

37.5 

15.0 

8.9 

13.8 

12.1 

2.6 

2.0 

5.9 

0.11

97.91

.73

Amphibole structural formula — 23 oxygens

Si . _

AlTM

AjVI

Al*"* 3 „

Fcn

Mo __ - mg 

•j| _______

Cr- - —

PI , -,

Wo

If

5.64 

2.36 

0.41 

2.77 

1.47 

2.72 

0.44 

0.005 

1.96 

0.78 

n?5

5.72 

2.28 

0.26 

2.54 

1.22 

2.91 

0.62 

0.002 

1.83 

0.74 

nvi

5.57 

2.43 

0.14 

2.57 

1.16 

3.05 

0.65 

0.004 

1.93 

0.74 

n^s

5.73 

2.27 

0.27 

2.54 

1.04 

3.05 

0.62 

0.005 

1.82 

0.71 

n-*«

5.59 

2.41 

0.13 

2.54 

1.16 

3.08 

0.65 

0.005 

1.92 

0.71

OT7

5.90 5.92 5.71 

2.10 2.08 2.29 

0.42 0.41 0.26 

2.52 2.49 2.55 

0.96 1.06 1.09 

2.98 2.91 3.03 

0.62 0.61 0.62 

0.03 0.003 0.002 

1.69 1.72 1.84 

0.64 0.65 0.72 

n T? n vi n ^R

5.63 

2.37 

0.19 

2.56 

1.10 

3.07 

0.64 

0.013 

1.88 

0.74 

OT7

5.58 

2.42 

0.19 

2.61 

1.10 

3.06 

0.66 

0.014 

1.88 

0.74 

n^R

5.59 

2.41 

0.22 

2.63 

1.11 

3.03 

0.65 

0.014 

1.85 

0.74 

n^R

5.55 

2.45 

0.17 

2.62 

1.10 

3.05 

0.66 

0.01

1.92 

0.75 

n^R

Papike A/R4 -
38 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

•s

o 

.o

I

I

' •*' oo ro ^1

^-H 1-* ^-H

vq vqcn o\cnr- 

' p

p •* oo CO-H

^ ^H ^H 1-H

O TfOO CO-H

^ 1-H 1-H l-H

ilvv —

i ! U.

\l

3

>o«s o «s -H CSOO-HOO <;

l-HCv|'—IOO

i p vopOvr-;
Table 6. Compositions of amphibole (kaersutite)—Continued.

Amphibole megacrysts from location 13 (exposures X, Y, Z-AM) 1 — continued

Sample No. Z1-AM1 Z2-AM1 Z3-AM1 Z3-AM2 Z4-AM1 Z4-AM2 Z4-AM3 Z4-AM4 Z4-AM5 Z4-AM6 Z4-AM7 Z4-AM8 

Analyses (weight percent oxide)

olv/2 """"• "-*— — TM

FeO^ 2 ———

MoO - - ——

CaO ______ 

Na->O

VQ __

TjQ, _______

Cr n

Total — — 

Mg ratio= 

Mg/(Mg+SFe)

40.0 

14.4 

7.9 

13.7 

10.8 

2.3 

2.0 

5.6 

0.20

96.90 

.76

40.0 

14.4 

8.1 

13.7 

10.8 

2.3 

10 

5.6 

0.14

97.04 

.75

39.5 

14.4 

9.8 

12.6 

10.9 

2.4 

2.0 

5.5 

0.03

97.13 

.70

39.6 

14.4 

9.2 

13.0 

10.8 

2.4 

2.0 

5.6 

0.04

97.04

.72

40.0 

14.5 

8.2 

13.7 

10.8 

2.4 

2.0 

5.8 

0.08

97.48 

.75

39.8 40.6 40.9 

14.4 14.5 14.7 

8.5 9.0 8.8 

13.4 13.2 13.6 

10.9 11.0 11.0 

2.4 2.3 2.4 

2.0 2.0 2.0 

5.7 5.6 5.7 

0.04 0.03 0.03

97.14 98.23 99.13 

.74 .72 .73

41.0 

14.8 

8.3 

13.9 

11.0 

2.3 

2.0 

5.7 

0.04

99.04

.75

40.8 

14.7 

8.7 

13.6 

11.0 

2.3 

2.0 

5.6 

0.03

98.73 

.74

40.6 

14.6 

8.2 

13.7 

11.0 

2.3 

2.0 

5.6 

0.05

98.05

.75

41.1 

14.6 

8.6 

13.8 

11.0 

2.3 

2.0 

5.7 

0.04

99.14

.74

Amphibole structural formula — 23 oxygens

Si — - - —

^ylV _____

Affi .„„ _ „

Al"*3 _____

pgH _____

j^|g _____

Ti ————~— 

£- ______

Ca

Na

|£ ______

5.89 

2.11 

0.39 

2.50 

0.97 

3.01 

0.62 

0.023 

1.70 

0.66 

0.37

5.88 

2.12 

0.38 

2.50 

1.00 

3.00 

0.62 

0.016 

1.70 

0.66 

0.38

5.86 

2.14 

0.38 

2.52 

1.22 

2.79 

0.61 

0.004 

1.73 

0.68 

0.38

5.86 

114 

0.38 

2.52 

1.14 

187 

0.62 

0.005 

1.71 

0.69 

0.38

5.86 

2.14 

0.37 

151 

1.00 

2.99 

0.64 

0.009 

1.70 

0.68 

0.37

5.87 5.92 5.90 

2.13 2.08 2.10 

0.37 0.41 0.40 

2.50 2.49 2.50 

1.05 1.10 1.06 

2.94 2.87 2.92 

0.63 0.61 0.62 

0.005 0.004 0.003 

1.72 1.72 1.70 

0.69 0.65 0.67 

0.38 0.37 0.37

5.90 

2.10 

0.42 

152 

1.00 

2.98 

0.62 

0.005 

1.70 

0.64 

0.36

5.91 

2.09 

0.42 

2.51 

1.05 

2.93 

0.61 

0.003 

1.71 

0.65 

0.37

5.91 

2.09 

0.41 

2.50 

1.00 

2.97 

0.61 

0.006 

1.72 

0.64 

0.37

5.92 

2.08 

0.40 

2.48 

1.04 

196 

0.62 

0.00

1.70 

0.64 

0.37

Papike A/R4-
40 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA

1

i

I

m -o

e!

— O

C>

8 P.

%

§;

85

§;

£

al —— o= 

g+SFe

Mg

23

•&

' — d o <

— 00 <

% g 5 S

•>C>»OCS--«SOC>-HOO <;

— O O oj

— O O p^

— 00 <

SS^SSSSPJS^

' —' o o <

— o o <
Table 6. Compositions of amphibole (kaersutite)—Continued.

Amphibole vein in Iherzolite xenolith (BC-2-21)

Sample No. Al A2 A3 A4 A5 A6

Amphibole of 

phlogopite-apa

(KPA

A7 KPA-A1 

Analyses (weight percent oxide)

MoO — _

CaO ———— 

NajO ————

IvyJ •»»««"•»••-

Cr2<$ 3 ———

Total —— 

Mg ratio= 

Mg/(Mg+SFe)

40.2 

14.7 

9.3 

13.4 

11.0 

2.4 

2.0 

5.6 

0.03

98.63 

.72

40.1 

14.7 

9.3 

13.4 

11.0 

2.4 

2.0 

5.6 

0.03

98.53 

.72

40.0 

14.7 

9.3 

13.3 

11.0 

2.4 

2.0 

5.6 

0.04

98.34 

.72

40.1 

14.7 

9.3 

13.4 

11.0 

2.4 

2.0 

5.6 

0.02

98.52 

.72

39.9 

14.7 

9.3 

13.3 

11.0 

2.4 

2.0 

5.5 

0.03

98.13 

.72

40.1 

14.7 

9.3 

13.4 

11.0 

2.4 

2.0 

5.6 

0.03

98.53 

.72

39.9 

14.5 

10.2 

12.8 

11.0 

2.4 

1.9 

5.6 

0.03

98.33 

.69

39.5 

14.4 

14.2 

9.9 

10.8 

2.6 

1.8 

5.2 

0.03

98.43 

.56

Amphibole structural formula — 23 oxygens

Si _ _ . _

AiFV __ ______

A] VI _____ _ ____

TJ __________

Na— ——— 

Papike A/R4 -

5.85 

2.15 

0.38 

2.53 

1.13 

2.91 

0.61 

0.003 

1.72 

0.67 

0.37

A

5.84 

2.16 

0.37 

2.53 

1.13 

2.91 

0.61 

0.004 

1.72 

0.68 

0.37

A

5.84 

2.16 

0.37 

2.53 

1.14 

2.89 

0.62 

0.005 

1.72 

0.68 

0.37

A

5.85 

2.15 

0.37 

2.52 

1.13 

2.91 

0.61 

0.002 

1.72 

0.68 

0.37

A

5.84 

2.16 

0.38 

2.54 

1.14 

2.90 

0.61 

0.004 

1.73 

0.68 

0.37

A

5.84 

2.16 

0.37 

2.53 

1.13 

2.91 

0.61 

0.004 

1.72 

0.68 

0.37

A

5.85 

2.15 

0.36 

2.51 

1.25 

2.80 

0.62 

0.004 

1.73 

0.68 

0.36

A

5.89 

2.11 

0.42 

2.53 

1.77 

2.20 

0.58 

0.004 

1.73 

0.75 

0.34

R

'Numbering of amphibole megacrysts (AM) from dike: prefix X, Y, Z refers to exposures, and numbers 1-5 are zones. 

2Total Fe expressed as FeO. 

3Total Al is a plotting parameter in figure 16A.

4 Analysis accepted (A) or rejected (R) by Papike and others (1969) screen for amphibole probe analyses. All "R" analyses listed were re

basis of one criterion and are indistinguishable from "A" analyses.



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