The Hallett Volcanic Province, 

Antarctica

GEOLOGICAL SURVEY PROFESSIONAL PAPER 456-C

Prepared on behalf of the 

National Science Foundation
The Hallett Volcanic Province, 

Antarctica

By WARREN HAMILTON

CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

GEOLOGICAL SURVEY PROFESSIONAL PAPER 456-C

Prepared on behalf of the 

National Science Foundation

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 77-187573

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 - Price 70 cents (paper cover)

Stock Number 2401-2054
CONTENTS

Page 

Abstract _________________ C 1

Introduction __________________________

Antarctica _ - ___ 

Ross Sea petrologic province ____________

Other work in northeastern Victoria Land 

Present work ____________________________

Offshore volcanoes ___________________________

General ____ ___ 

Crustal setting __ _______________

Coulman Island _ _ _______

Coulman caldera ___________________

Daniell Peninsula ______________________

Basement rocks __ 

Hallett Peninsula _______ ______

Eastern belt _________ ____

Northern volcano ____ _______

Eastern volcanoes _________

Southeastern volcano ____________

Southwestern volcanoes _____________

Seabee Hook ___________________

Adare Peninsula ________________________

Southern dome ________________

Northern peninsula ______________

Ridley Beach ________________________

McCormick Island ________________

Possession Islands ___________________

Age of volcanic rocks _______________

Bathymetry __________________

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Offshore volcanoes Continued

The breccias _______________ _ C27

Palagonite breccia ______________

Palagonite tuff ________________

Palagonite ___________________

Nodular lavas ____________________

Megapillows __________________

The breccias and glaciation ______________

Prior ice levels ________________

Ice-contact breccias of Iceland ________

Origin of the Antarctic breccias ______

Late Cenozoic glaciation of Antarctica 

Erosion __________________ .

Volcanic rocks of the mainland ______________

Volcanic rocks north of 73° S. latitude ____

Mount Overlord and Mount Melbourne ____

Petrology _________ ___ ___________

Rock classification ______________________

Distribution of rock types _______________

Petrography ____ _ _ __________

Ultramafic inclusions ____________

High-pressure megacrysts __________

Descriptions of analyzed specimens _- 

Chemistry ___________________________

Major oxides ________________

Minor elements _______________

Petrologic comparisons _______________

References cited ____________________

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ILLUSTRATIONS

	Page

FIGURE 1. Map showing tectonic and volcanic provinces of Antarctica ____________________________ C 2

2. Map showing upper Cenozoic volcanic rocks of the Ross Sea region _____________________ 3

3. Photograph of Borchgrevink's huts at Ridley Beach, Cape Adare _______________________ 4

4. Map of northeastern Victoria Land, showing distribution of pre-Tertiary rocks and of upper Cenozoic

	volcanic rocks _______.______________________________________________ 6

o. Aerial view southward over Moubray Bay _____________________________________ 7

6. Map of Coulman Island and the southern part of Daniell Peninsula ______________________ 8

7. Aerial view southward along Coulman Island ____________________________________ 9

8. Photograph showing outward-dipping breccias of northwestern Coulman Island ____________ 9

9. Photograph of young basaltic cinder cone, Coulman Island ____________________________ 10

10. Aerial view northward along Daniell Peninsula ____- -__ -__ - __ 11

11. Aerial views westward over Daniell Peninsula - ___ 12

12. Photograph southward across Tucker Glacier to Daniell Peninsula __ ___.._ 13

III
IV CONTENTS

	Page

FIGURE 13. Photograph of basement rocks beneath basaltic breccias, Daniell Peninsula CIS

14. Shaded-relief map of Hallett Peninsula and northern Daniell Peninsula 15

15. Aerial views westward over ends of Hallett Peninsula 16

16. Aerial view northward over Hallett Peninsula ______ _ 17

17. Shaded-relief map of Adare Peninsula region _ ____ _ _ 19

18. Photograph of Mount Harcourt from Tucker Glacier , ____ 20

19. Aerial view of Cape Hallett and Seabee Hook 20 

20-23. Aerial views:

20. Eastward to Adare Peninsula _ _ __-- 21

21. Shield volcano of Adare Peninsula __ 22

22. Ridley Beach _______________________ _ __ _ ___, 23

23. The islands east of Adare Peninsula 24

24. Bathymetric map of the northwestern Ross Sea - -- - 26 

25-30. Photographs:

25. Breccias of Hallett Peninsula _____________-_ - - - _ 28

26. Breccias of Coulman Island ____________ _ 31

27. Palagonite breccia of Coulman Island ______ ______ _ 32

28. Palagonite tuff ____________________________________________________ 34

29. Nodular lavas _____________________________________________________ 36

30. Megapillows ______________________________________________ _____ 38

31. Schematic profile showing ice levels when continental ice sheet overrode Cape Adare ___ _ 39

32. Aerial views of stratovolcanoes ______________________________ _ 43

33-35. Diagram showing:

33. Contents of K2O and Na2O _______________________________________________ 54

34. Magnesia variation _____________________________________________ 55

35. Iron in the volcanic rocks ________-__________________________________ 56

36. AFM diagram ____________________________________________________r_______ 56

37. Ternary diagram of CaO, Na2O, and K2O ________________________________________ 56

38. Variation diagram of P2O5, Cl, F, and MnO _____________________________________ 57

39. Variation diagram of minor elements _______________________________________ 58

40. AFM diagram for several basalt-and-trachyte provinces _____________________ __ 59

TABLES

Page

TABLE 1. Potassium-argon dates from whole-rock samples of basalt low in the volcanic piles of the Hallett province __ C25

2. Chemical analyses and calculated components of volcanic rocks of Hallett Peninsula _______________ 48

3. Chemical analyses and calculated components of volcanic rocks of Hallett Province, other than Hallett

Peninsula _________________________________.._____________________ 50
CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

THE HALLETT VOLCANIC PROVINCE, ANTARCTICA

By WARREN HAMILTON

ABSTRACT

The Hallett volcanic province of upper Miocene to Holocene 

sodic basalt and trachyte lies along the Ross Sea coast of 

northeastern Victoria Land. The volcanic rocks occur primarily 

in four long offshore piles: one wholly an island (Coulman), 

the other three (Daniell, Hallett, and Adare Peninsulas) 

joined to the mainland by ice-filled troughs. Each pile is a 

broad elongate dome formed by eruptions mostly along a 

crestal fissure zone. The Daniell and Coulman domes remain 

symmetrical, but the Hallett and Adare piles were erupted 

mainly from vents east of the present peninsulas, the eastern 

half of each edifice having been since eroded away. The broad 

conical volcanoes rise gently above the general crests to altitudes of about 2,000 meters and are marked by large calderas.

Each volcanic dome consists mostly of subglacial palagonitic 

breccias and pillow-breccia complexes of spectacular character, 

erupted during late Miocene, Pliocene, and Quaternary times, 

when the Antarctic ice sheet \vas grounded on the Ross Sea 

shelf and \vas far more extensive that it is now. The breccias 

are capped by subaerial lavas and scoria.

Small masses of upper Cenozoic volcanic rocks occur on the 

pre-Tertiary rocks of the mainland, west of the offshore piles, 

and several large volcanoes also are present on the mainland.

The volcanic rocks belong to a sodic basalt-and-trachyte association. Mafic rocks, particularly alkaline olivine basalt and 

trachybasalt, are dominant; but more felsic rocks, including 

latite, trachyte, extremely sodic phonolite, and relatively potassic quartz trachyte, are abundant.

INTRODUCTION

The Hallett volcanic province consists of accumulations of upper Miocene, Pliocene, and Quaternary 

basalt and trachyte along the Eoss Sea coast of 

northeastern Victoria Land. Most of the rocks apparently were erupted under ice which filled the 

present Eoss Sea and which stood several kilometers 

above present glacier levels; the result was the formation of thick piles of breccias. The rocks are in general remarkably high in alkalis and include some of

the most sodic igneous rocks known anywhere. This 

report describes the occurrence and petrology of these 

unusual volcanic rocks, with emphasis placed on physical volcanology.

ANTARCTICA

If its ice cap were melted, Antarctica would consist 

of one large landmass and many small ones (fig. 1). 

The large mass is about the size of Australia or the 

United States and is named East Antarctica because it 

is mostly restricted to east longitudes. The smaller 

masses collectively form West Antarctica, are limited 

to west longitudes, and comprise large and small 

islands rising from a continental platform which 

would be largely submerged even after isostatic rebound. These various large and small masses are now 

bridged by the continental ice cap.

East Antarctica consists of a Precambrian shield 

and, broadly coextensive with the high Transantarctic 

Mountains along the Eoss and Weddell Seas, a late 

Precambrian and Paleozoic mobile belt (fig. 1). West 

Antarctica consists of Paleozoic and Mesozoic geosynclinal and plutonic rocks. For reviews of the geology of these provinces, the reader is referred to recent 

summary reports: Adie (1962), Andersoii (1965), 

Ford (1964), Gunn (1963), Hamilton (1967a), Harrington (1965),Klimov, Eavich, and Solov'yev (1964), 

Eavich (1965), Eavich, Klimov, and Solov'yev (1965), 

Voronov (1964), and Warren (1965). The 76 reports 

on Antarctic geology in the compendium edited by 

Adie (1964) provide much information on detailed 

work, and the fine Soviet atlas of Antarctica (Bakayev, 1966) presents in cartographic form a wealth of 

topographic, geologic, glaciologic, climatic, and 

oceanographic data.

Cl
C2 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

VOLCANIC ISLAND; ' ' AUS

:; MESOZOIC eEOSYNCLINE

>' Cuirtiinatliig jJetermattWi artd m- I \ - :

of diorite, quartz diorite, 

; :;;-! ' and granodiorite during Cretaceous

 \ WEST 

l ANTARCTIQA

; ; Cenozoic andesite, basalt, and decile

widespread on Mesozoic basement

, : ;v roch$

CENOZOIC VOLCANIC TERRANE 

Varied alkaline and calc-alkaline rocks

 "^H^"^1 >^lt>^ -: .- -1 - *

McMURDD VOLCANIC PROVINCE 

Alkaline otivine basalt and trachyte

FIGCRE 1. Tectonic and volcanic provinces of Antarctica, showing location of Hallett Volcanic Province (lower center). Adapted from

Hamilton (1967a, fig. 1). Line pattern, volcanic provinces.

The Hallett volcanic province of upper Miocene to 

Holocene basalt and trachyte lies in northeastern Victoria Land, along the Ross Sea coast of the Transantarctic Mountains south of New Zealand. The prevolcanic rocks of this corner of Victoria Land consist of 

very thick clastic sedimentary rocks, metamorphosed at 

low grade and intruded by numerous small plutons 

of granodiorite of Late Devonian or early Carboniferous age.

ROSS SEA PETROLOGIC PROVINCE

Upper Cenozoic basalt and trachyte form large 

volcanic piles scattered from the McMurdo Sound 

region to the Balleny Islands (fig. 2).

Harrington (1958) proposed that all the Cenozoic 

volcanic rocks of the Ross Sea sector of Antarctica 

be referred to a single formation, the "McMurdo 

Volcanics." The rocks share petrologic characteristics 

 most are alkaline olivine basalts and sodic trachytes
HALLETT VOLCANIC PROVINCE C3

160° 170°

SOUTHERN

INLAND ICE 

PLATEAU

Beaufort 

Island^ 

McMURDO

SOUND 

Mount 

Ereb

MeMURPO 

VOLCANIC 

island PROVINCE

Mount Terra Nova , ,

Mount Terror *' -. 

Hut Point 

Brown Peninsula

White Island 

Black island ,v

MbmaSiuff 

Maant Discovery 

Mount Morning

75

150°

50

I

100 150 200

I

250 KILOMETERS

APPROXIMATE

FIGURE 2. Upper Cenozoic volcanic rocks (shaded) of the Ross Sea 

petrologic province. *, major young volcanic cone. Minor clusters 

of small cones and flows on the mainland are omitted. Base from 

1 : 5,000,000 map of Antarctica by American Geographical Society, 

1965.

and they overlap in age at least in the Quaternary. 

The rocks certainly belong to a broad petrologic province, but referring them all to a single formation is 

of dubious utility, and the designation is not used 

here.

I will here instead refer to all the volcanic rocks 

shown in figure 2 as belonging to the Ross Sea petrologic province, and within this broad category will 

designate three major subprovinces the McMurdo 

volcanic province (Mount Morning to Boss Island), 

the Hallett volcanic province (Coulman Island to 

Adare Peninsula), and the Balleny volcanic province. 

This leaves unattached the Beaufort, Franklin, Melbourne, and Overlord volcanic centers.

Each of the three major volcanic subprovinces so 

classified has a distinctively different occurrence. The 

McMurdo volcanic province is characterized by high 

subaerial volcanoes. The Hallett volcanic province consists of long coastal domes of subglacial breccias, surmounted by low subaerial volcanoes. The volcanoes of 

the Balleny province also form long domes, but these 

rise from the deep ocean.

Imposing volcanoes stand high above broader volcanic platforms in the McMurdo Sound region and 

form the high peaks of Boss Island and also of Mounts 

Discovery and Morning. A noteworthy volcanic form is 

that of the high rounded uncratered summit dome of 

Mount Discovery, which may be a large extrusive 

trachyte dome. Published information consists mostly 

of sample descriptions and is scattered widely through 

the Antarctic literature. During my own brief examinations of Hut Point Peninsula, the southeast slope of 

Mount Terror, White and Black Islands, Brown 

Peninsula, Minna Bluff, and Mount Discovery, I saw 

palagonite breccias, likely products of subglacial 

eruptions, only on Minna Bluff, and at Castle Bock on 

Hut Point Peninsula. The other exposed volcanic rocks 

that I have seen in the McMurdo volcanic province 

are products of subaerial eruptions basalt flows and 

cinders, trachyte flows and domes.

Mounts Melbourne and Overlord are dominant volcanoes farther north in Victoria Land.

Each of the long volcanic pile® Coulman Island 

and Daniell, Hallett, and Adare Peninsulas in the 

Hallett volcanic province consists of a thick foundation of spectacular subglacial breccias and a topping 

veneer of subaerial eruption products and low volcanoes. The breccia piles face the Boss Sea with 

straight, sheer cliffs whose heights reach nearly 2,000 m 

(meters).

The possibility that Boss Island and the other main 

McMurdo volcanic centers are connected to Coulman 

Island and the coastal peninsulas by extensive sub-
C4 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

marine accumulations of volcanic rocks is eliminated 

by results of aeromagnetic surveys; submarine veneers 

of lava, however, could be present. The surveys show 

that high-amplitude, short-wavelength magnetic anomalies in the western Ross Sea are confined largely to 

the exposed volcanic piles and the neighboring areas 

(Eobinson, 1964; Behrendt, 1964; Behrendt and Bentley, 1968, pi. 7).

The Balleny volcanic province consists of three 

elongate islands and a few islets rising from the ocean 

northwest of Cape Adare (fig. 2, this rept,; Dawson, 

1969a, b, c; Mawson, 1950). Like the Coulman, Hallett, and Adare piles, the Ballenys are cliff sided and 

ice capped. Photographs (Hatherton and others, 1965, 

figs. 6, 7) show what appear to be breccias like those of 

the Hallett volcanic province: eruptions beneath ice 

caps may be indicated. Alkaline olivine basalts are 

present (Mawson, 1950).

OTHER WORK IN NORTHEASTERN VICTORIA LAND

In January 1841, a Royal Navy research expedition 

of the two ships Erebus and Terror, commanded by 

James Clark Boss, made the first penetration of the 

Antarctic pack ice and entered the Ross Sea. A landing was made at Possession Island, and the volcanic 

rocks collected were described by Prior (1899).

No one entered the region again until 1894, when 

whale-crewman C. E. Borchgrevink landed at Ridley 

Beach, Cape Adare, and collected volcanic-rock specimens subsequently described by David, Smeeth, and 

Schofield (1896). Borchgrevink later promoted an 

expedition of his own and returned in 1898. Two huts 

were built at Ridley Beach (fig. 3), and Borchgrevink 

and nine others remained there nearly a year. They 

were the first men to winter in Antarctica. Several published reports including that by Prior (1902) describe 

the rock specimens they collected, mostly upper Cenozoic volcanic rocks, about Robertson Bay and along 

the Ross Sea coast.

During Robert Falcon Scott's expedition of 1910- 

13, a six-man party, including geologist Raymond 

Priestley, built another hut at Ridley Beach and remained there from February 1911, until January 

1912, conducting man-haul sledge excursions about 

Robertson Bay. They spent the following summer 

farther south in northern Victoria Land, where they 

were then marooned overwinter in an ice cave on a 

seal-and-penguin diet. Priestley (1923) described some 

of the geologic findings. The volcanic rocks collected 

from the Adare Peninsula and Terra Nova Bay regions 

were well described long afterward by Smith (1959; 

1964a, b).

FIGURE 3. Borchgrevink's huts at Ridley Beach, Cape Adare, as they 

appeared in November 1964. These structures, the first built in 

Antarctica, were occupied by the first party to winter on the continent, during 1898 and 1899. The living-quarters hut (foreground) 

is still in good condition, but the stores hut beyond has lost its 

roof and has partly collapsed.

The modern era of exploration began with the 

establishment by many nations of logistic and research 

stations in the Antarctic for the International Geophysical Year. Hallett Station was built in early 

1957 and is operated jointly by the United States and 

New Zealand. A snow-cleared landing strip on the 

sea ice of Edisto Inlet handles wheeled aircraft each 

spring.

A geologic reconnaissance of the region was carried 

out from Hallett Station by an eight-man New Zealand party led by H. J. Harrington during the 1957- 

58 summer. The party traveled about Edisto Inlet 

and up the Tucker Glacier. Their geologic findings 

were reported by Harrington, Wood, McKellar, and 

Lensen (1967).

Three small New Zealand parties operated in northern Victoria Land during the 1962-63 summer. One 

explored the region from Mount Overlord to the upper 

Rennick Glacier (Gair, 1964, 1967), one the region 

south of Priestley Glacier (Skinner and Ricker 

1968a, b), and the other the region southwest of 

upper Tucker Glacier (Le Couteur and Leitch, 1964). 

A six-man New Zealand party made a far-ranging 

sledge exploration in the summer of 1963-64 (Sturm 

and Carryer, 1970). Small New Zealand geologic parties operated in the southern part of northern Victoria Land during the 1965-66 and 1966-67 summers 

(Adamson and Cavaney, 1967; Nathan and Schulte, 

1967, 1968; Riddolls and Hancox, 1968). The geologic 

map compiled by Gair, Sturm, Carryer, and Grindley 

(1969) incorporates most published mapping.
HALLETT VOLCANIC PROVINCE C5

PRESENT WORK

The late Dwight F. Crowder and Donald A. Coates 

and I made a geologic reconnaissance study of 50,000 

sq km (square kilometers) of northeastern Victoria 

Land during November 1964. The work was done by 

means of helicopters operating from Hallett Station. 

Crowder and Coates worked primarily with the metamorphic and granitic rocks of the mainland, whereas 

I concentrated on the Cenozoic volcanic rocks along 

the coast. Several brief summaries of the geologic results have been published (including those of Crowder 

and Hamilton, 1966, and Hamilton, 1965, 1967b), as 

has one longer report on the prevolcanic rocks (Crowder, 1968).

The work was supported by a grant to the U.S. Geological Survey from the Office of Antarctic Programs 

of the National Science Foundation. Air transportation to and from Hallett Station, by w^ay of New 

Zealand and McMurdo Station, Antarctica, was provided by the U.S. Navy. The Navy also provided quarters and meals at Hallett.

Transportation in the field was provided by the 

three Bell UH-IB (Iroquois) helicopters of the U.S. 

Army Antarctica Support Aviation Detachment, commanded by Maj. W. C. Hampton. Pilots were Maj. 

J. B. Muck and CWO's J. J. Lockhart, J. S. Eeid, and 

D. M. Shanklin. The cooperation of these men and 

the others in the detachment made possible the rapid 

study of a very large region, despite the difficult field 

conditions.

The high-performance turbine helicopters have high 

cruising speeds and rates of climb and are ideal for 

reconnaissance studies. A typical field day involved 

several hundred kilometers of flying plus perhaps five 

stops for sampling and study of rock outcrops. Geologic mapping was done mostly from the air: snow 

and ice cover is extensive, but rock exposures where 

present are generally superb.

My work on the volcanic rocks utilized 10 field days, 

and Crowder and Coates each worked with volcanic 

rocks on 2 days. Between us, we studied and sampled 

about 60 volcanic localities on the ground. The major 

volcanic piles (Coulman, Daniell, Hallett, and Adare) 

were each sampled in a number of places and were 

examined from the air throughout their extent. Most 

minor volcanic accumulations near the coast and north 

of latitude 73° S. were sampled also.

For field base maps, we used 1: 250,000 enlargements 

of a prepublication edition of the 1: 500,000 shadedrelief Northeastern Victoria Land sketch map, prepared from trimetrogon photographs controlled by

ground tellurometer survey and triangulation (MacDonald, 1968) and later published by the U.S. 

Geological Survey. Topographic maps at a scale of 

1 :250,000 \vere subsequently prepared from the trimetrogon photographs but were published too late for 

incorporation in the maps of the present report. (The 

Hallett volcanic province lies within the area of three 

of the Survey's 1:250,000 Antarctica Reconnaissance 

Series maps: Cape Adare, SR 59-60/13, 1970; Cape 

Hallett, SS 58-60/2, 1970; and Coulman Island, SS 

58-60/6, 1969.) We also used the trimetrogon aerial 

photographs, \vhich had been taken by the U.S. Navy 

for the U.S. Geological Survey, for both field recording and photointerpretation. Of the altitudes noted in 

this report, some are geodetic determinations from the 

Northeastern Victoria Land sketch map, some are approximate altitudes from New Zealand and U.S. Navy 

maps, others are helicopter aneroid altimeter measurements, and some are estimates scaled on photographs 

with known dimensions. Attitudes of rocks on the maps 

were estimated from photographs.

Color slides taken freely yielded much information 

where careful field observation and recording were precluded by the pace of the fieldwork. Telephoto-lens 

pictures, providing closeups within large areas put in 

context with normal and wide-angle photographs, permitted office study of details with results comparable 

to field examination with binoculars. Lenses as long 

as 200 mm (millimeters) were used on hand-held 

35-mm cameras. Photographs in this report not otherwise credited were taken by me.

Daily maximum and minimum air temperatures at 

sea-level Hallett Station during the month of fieldwork were typically about -4° and -12°C (10° 

and 25°F) warm, by Antarctic standards, because 

of the coastal and northerly position of the station. 

Temperatures were far colder inland and at high 

altitude. Winds were generally from the south. Coastal fogs become a problem as open water progresses 

southward during early summer; during our November season, fog was common only in the Adare Peninsula region. Summaries of weather data from 

Hallett were presented by Rudolph (1966) and by 

Harrington, Wood, McKellar, and Lensen (1967, p. 82).

Four potassium-argon age determinations of basalts 

were generously made by Richard Lee Armstrong of 

Yale University in 1968, and are incorporated in this 

report.

This report was largely completed during 1969, although minor corrections and additions were made as 

late as 1971.
C6 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

164° 166° 168° 170°

71°

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FIGURE 4. Northeastern Victoria Land, showing distribution of pre-Tertiary rocks (light shaded) and of 

upper Cenozoic volcanic rocks (dark shaded). Base map adapted from an unpublished compilation 

by the American Geographical Society, 1967. The numbers are sample locality numbers used in the 

text.
HALLETT VOLCANIC PROVINCE C7

OFFSHORE VOLCANOES

GENERAL

The volcanic rocks of the HaFett province occur 

primarily in four long piles along the west side of the 

northern Boss Sea (figs. 4, 5). One of these piles is 

wholly an island (Coulmaii), and the other three 

are peninsulas (Daniell, Hallett, and Adare) which 

are largely separated from the mainland by troughs 

filled with grounded and floating ice. The rocks are 

of late Miocene to Holoceiie age.

Each of these major volcanic piles is a broad elongate dome formed by the coalescing of basalt and 

trachyte erupted mostly from vents along a crestal 

fissure zone. The Daniell and Coulmaii domes remain 

symmetrical, the main vent zones trending along their 

midlines. The Hallett and Adare piles were erupted in 

considerable part from vents east of the present edges 

of the peninsulas, the eastern half of each dome having been since eroded away. The small Possession 

Islands, east of southern Adare Peninsula, may be

remnants from the eastern part of the Adare dome.

Broad conical volcanoes rise gently above the general crestal levels to altitudes typically of about 

2,000 m. Some of these volcanoes are marked by large 

calderas. Recent cinder cones along each crest attest 

to continuing activity. (Harringtoii and others, 1967, 

also recognized some of the volcanic features referred 

to in this report.)

Each volcanic pile consists mostly of subglacial 

palagonitic breccias and pillow-breccia complexes of 

spectacular character, erupted during late Miocene, 

Pliocene, and Quaternary times under the Antarctic 

ice sheet which was grounded 011 the Eoss Sea shelf 

and which was far more extensive than it is now. The 

capping rocks of each pile are subaerial lavas and 

scoria, formed after the eruptions overtopped the ice.

Small masses of upper Cenozoic volcanic rocks occur 

011 the pre-Tertiary rocks of the mainland, west of 

the large volcanic piles, and several large volcanic 

masses occur 011 the mainland farther west and southwest of the southern of the domes.

FIGURE 5. Aerial view southward over Moubray Bay, showing relation of elongate volcanic piles to the mainland. Hallett Peninsula is at 

left center, Daniell Peninsula is beyond its right part, and Coulman Island is on the left skyline (130 km from the foreground ridge). 

Hallett and Daniell volcanic rocks are separated from the pre-Tertiary rocks of the mainland mountains by bays and glacier-filled 

troughs. Mount Herschel (right center) rises precipitously above floating Ironside Glacier, and stands 3,335 m (meters) above the windstreaked sea ice. Photograph TMA 1036 F33, no. 180, by U.S. Navy for U.S. Geological Survey, altitude 7,600 m, 25 November 1962.
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HALLBTT VOLCANIC PROVINCE C9

CRUSTAL SETTING

The high mountains of pre-Cenozoic rocks slope 

steeply into the Boss Sea from altitudes of 2,000 to 

more than 3,000 m (fig. 24), and the offshore volcanic piles of the Hallett province rise from the 

continental shelf, which is typically about 500 m below 

sea level. Presumably normal faults and abrupt flexures 

bound the Boss Sea, although the actual structural 

features have yet to be mapped and can only be 

inferred from the topography. Rocks like those of the 

mainland continue beneath the volcanoes, as indicated 

by an island of granodiorite that projects into the 

basalts of the east side of Daniell Peninsula and by 

granitic xenoliths that occur in a cinder cone on 

McCormick Island, east of Adare Peninsula.

The scarps along the Ross Sea coast must reflect an

FIGURE 7. Aerial view southward along Coulman Island. Coulman 

caldera at the far end is 6 km in diameter. The fast sea ice

f encloses tabular icebergs as seen at the bottom of the picture and 

is darkened by emperor penguin rookeries to the right of the near 

end of the island. Photograph by U.S. Navy for U.S. Geological 

Survey, TMA 1037, F 31, no. 191, altitude 7,600 m, 25 November 

1962.

abrupt westward thickening of the continental crust 

and deepening of the Mohorovicic discontinuity 

(Behrendt and Bentley, 1968). Intense volcanism 

has occurred in the narrow transitional zone between continental-shelf and mountain-region crustal 

structures.

COULMAN ISLAND

The southernmost of the big breccia piles is Coulman 

Island (fig. 6). The island is 33 km long in the northsouth direction, and widens southward from 5 km near 

the north end to 14 km near the south end. Cliffs ring 

the island, whose broad, ice-capped central crest rises 

gradually southward to the caldera-truncated cone 

which dominates the island (fig. 7). Most of the rocks 

probably were erupted from the zone, now marked by 

the axial crest and the caldera, along the center of the 

island.

The lower 200-500 m of the volcanic section exposed about most of the island consists of massiveoutcropping palagonite breccias and pillow breccias. 

This lower section generally forms dark, unbroken 

cliffs that rise abruptly from the sea; this entire lower 

section stands as a vertical wall in many places (figs. 

7, 26). The breccia section above these lower cliffs is 

commonly more thinly bedded and produces cliffs 

sloping typically between 50° and 60°. Much snow and 

thin ice cling to these upper cliffs, which rise to 700- 

1000 m around most of the island. The overall slope 

of the 750-m cliffs along the south coast, westward for 

7 km from Cape Anne, reaches 80° in several places.

Dips in the breccias are low, generally less than 10° 

(fig. 6). The dips tend to be outward from the long 

axis of the island (figs. 7, 8). There are, however,

FIGURE 8. Outward-dipping breccias of northwestern Coulman Island, 

7 km south-southwest of Cape Wadworth. Dips flatten toward the 

observer. The grounded ice apron is fed by avalanches from the 

ice cap; a recent avalanche forms a large lobe. Relief shown in 

picture is about 1,100 m. The foreground sea ice is a rookery 

area for emperor penguins. 7 November 1964.
CIO CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

places, as in the cliffs west of Coulmaii caldera, where 

the section dips gently into the island.

COULMAN CALDERA

Coulman caldera, here named, truncates a high, 

broad cone w^hich stands on the wide southern part 

of the island (figs. 6, 7). The circular caldera rim is 

about 6 km in diameter and has an altitude of 

1,900-2,200 m. The rim forms a sharp ice divide, 

along which project narrow, discontinuous outcrops 

of subaerial trachyte lavas that dip 20°-25° radially 

outward. The broad ice dome in the center of the 

caldera, through w^hich no rock projects, perhaps caps 

a postcollapse trachyte dome. The caldera rim is 

breached by outlet glaciers, w^hich avalanche to the 

sea, on the northeast and south.

The caldera has a depth of at least 700 m. At the 

southern breach the inner rim of the caldera, covered 

by steep ice, has a height exposed above the calderafilling ice of about 300 m. The scarp continues downward between the east wall of the southern breach 

and the outlet glacier for an additional exposed height 

of about 400 m and appears, in an oblique photograph, 

to have a general slope of about 60°.

The caldera cone is exposed in section in the inaccessible cliffs which extend southward for 6 km from 

the south-central breach in the caldera rirn. At the 

north end of these cliffs the east edge of the southern 

outlet glacier the inner rim of the caldera as noted 

previously has a total exposed height of about 700 m, 

but the thinly layered lavas of the caldera cone are 

only about 300 m thick. Beneath them, much more 

massive rocks palagonite breccias? extend down to 

the ice apron. The thin-bedded lavas dip gently southward parallel to the top of the ice-capped ridge. The 

contact of lava over breccia is exposed for about 3 km 

southward along the cliffs, beyond which it is covered 

by ice cascading from the ice cap. The subaerial lavas 

do not reach the south end of the island, where the 

cliffs are entirely of the breccia series. The breccias 

display rough bedding subparallel to that of the overlying lavas in the cliffs that extend south from the 

caldera. The breccias may represent subglacial eruptions from the caldera center before the capping subaerial cone was formed. Or perhaps the breccias include 

downdip subglacial equivalents of the subaerial lavas.

The contact between lavas and breccias is hidden 

beneath ice around most of the caldera. The contact 

was however also observed at the west side of the 

southern outlet glacier, where lava is poorly exposed. The cliffs that extend westward from this locality are entirely of breccia. The lower cliffs along the 

w^est coast of the island also are everywhere of breccia; the upper cliffs west of the caldera appear from 

a distance to be similarly of breccia.

Several small cinder cones project through the 

Coulman Island ice cap. The best preserved and exposed of these cones lies two-thirds of the way dow^n 

on the north slope of the cone of Coulman caldera, on 

the axis of the island (fig. 9). Cinders collected from

FIGURE 9.- Young basaltic cinder cone projecting through the Coulman Island ice cap. This cone is on the north slope of the broad 

cone of Coulman caldera, and lies on the inferred axial fissure zone 

of the island. 7 November 1964.

this small cone are basaltic. The rim of another small 

cinder cone is exposed discontinuously through the ice 

cap, as seen in the low^er left part of figure 7.

The southwestern coast of Coulman Island is indented by a semicircular bay, 7 km in diameter (fig. 

6), w^hich perhaps is another caldera, much modified 

by erosion.

DANIELL PENINSULA

The elongate volcanic pile of Daniell Peninsula 

trends south-southwestward along the coast, south 

from Tucker Glacier (figs. 4, 6, and 14). The peninsula is 70 km long and as much as 20 km wide. The 

northern two-thirds of Daniell Peninsula is a broad 

symmetrical dome (figs. 10, 11), whereas the southern 

third is embayed deeply by erosion. Ice-filled troughs 

separate the peninsula from the mainland mountains 

of Paleozoic rocks. Were the ice to melt, the peninsula 

would be almost an island, connected only by a short 

saddle between the heads of long fiords.

The volcanic pile is ringed by cliffs. Around the 

northern symmetrical part, the cliffs are 100-900 m 

high. On the west they are almost entirely covered by 

ice falls, and on the east they are discontinuously covered. Cliffs are higher in the deeply eroded southern 

part of the peninsula but are largely mantled by ice. 

The slopes and crest above the cliffs are almost everywhere ice covered.
HALLETT VOLCANIC PROVINCE Cll

The domical form of the northern two-thirds of 

the peninsula indicates formation from overlapping 

volcanoes concentrated along a crestal fissure zone. 

From the north end ait Tucker Glacier, the crest rises 

southward to a prominent volcano, about 2,000 m high, 

thence drops to a level of about 1,500 m until the 

2,000-m volcano of Mount Brewster is reached farther 

south. A broad upland just south of the southern high 

point perhaps marks an eroded, ice-filled caldera on 

the crest (fig. 115). A crater indents the north end of 

the peninsula, and opens onto Tucker Glacier (fig. 12). 

The breccias and lavas exposed in the eastern cliffs 

jf the peninsula dip outward, subparallel to the ice3overed surface above the cliffs.

The irregularly embayed southern part of the peninsula appears to be formed of overlapping volcanoes 

broken by two large deep breached calderas. The most 

obvious volcano is small Mount Lubbock, about 1,500 

m high, wThich forms the south end of the peninsula. 

Between Mount Lubbock and the broad dome of the 

central part of the peninsula, two subcircular bays

cut far into the east side of the peninsula (figs. 6, 

10, 1L4, 115) and probably originated as calderas 

centered on the crestal fissure zone.

The eastern cliffs along the northern third of 

Daniell Peninsula are relatively well exposed. The 

lower half of the section is typically palagonite breccias and pillow breccias, whereas the upper half is 

mostly interlayered maroon and gray lavas which 

contain sparse palagonite lenses. The cliffs of the central third are mostly covered by icefalls, but the fewr 

avalanche-cleared sections seen from the air appear to 

mostly have a similar contrast between lower breccias 

and upper lavas. Well-exposed cliffs 550 m high at the 

headland 8 km northeast of Cape Phillips expose only 

assorted breccias and pillow complexes. No field examination was made of the peninsula south of this headland. The few exposures seen of the cliffs on the west 

side of the peninsula, along Whitehall Glacier, are 

breccias. Holocene cinder cones project through the 

ice that covers the high northern volcano.

FIGDRE 10. Aerial view northward along Daniell Peninsula. Coalescing volcanoes along a crestal fissure zone have produced the broad 

dome. The large circular embayment below the center of the photograph probably marks a breached caldera. The floating ice shelf to 

the right of the embayment meets fast sea ice in the right foreground. In line with the peninsula to the north, across the trough of 

Tucker Glacier, is Mount Harcourt volcano of Hallett Peninsula. The higher peaks on the skyline reach altitudes of 4,000 m and are 

170 km away. Photograph TMA 1037-F33, no. 197, by U.S. Navy for U.S. Geological Survey, altitude 7,600 m, 25 November 1962.
C12 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

D

FIGURE 11. Overlapping aerial views westward over Daniell Peninsula. 

Volcanic eruptions occurred mostly along the crest of the peninsula, 

which is 70 km long. The cliffs are formed largely of ice-contact 

palagonite breccias. Glacier-filled troughs separate the peninsula 

from the mainland mountains of pre-Tertlary rocks; the farthest 

skyline ranges are about 300 km distant. A, Most of the southern 

part of the peninsula is embayed deeply by erosion, probably by 

the breaching of two calderas. The young volcano of Mount 

Brewster (~2,000 m) forms the southern tip. B, The broad upland 

left of center stands about 2 km above sea level and may be an

ice-filled caldera. Cape Phillips Is In the left foreground. C, The 

palagonite cliffs on the right are about 1,000 m high. A floating 

ice shelf extends from the foot of the cliffs to the fast sea ice. D, 

Many outcrops mark the flanks of a volcanic dome right of center. 

A dark cinder cone stands on the far side of the ridge near the 

right end (Cape Daniell). Whitehall Glacier fills the trough 

separating the peninsula from Mount Northampton (2,500 m; the 

dominant peak right of center). Photographs TMA 712, F31, nos. 

6, 12, 16, and 20, by U.S. Navy for U.S. Geological Survey, altitude 

6,000 m, 3 November 1960.
HALLETT VOLCANIC PROVINCE C13

FIGURE 12. View southward across Tucker Glacier to the north end of Daniell Peninsula. The breached crater, and the broad volcano, 2,000 

m high, of the skyline, are on the crestal fissure zone of the peninsula. 10 November 1964.

BASEMENT ROCKS

The only prevolcanic rocks exposed beneath any of 

the volcanic piles are present in cliffs 10 and 13 km 

northeast of Cape Phillips (figs. 6, 13), where an

FIGURE 13. Basement rocks beneath basaltic breccias, east side of 

Daniell Peninsula 10 km northeast of Cape Phillips. The contact 

between light-colored Paleozoic granodiorite and dark Cenozoic 

basalt slopes down to the left through the center of the picture. 

The cliff on the right is about 200 m high. 26 November 1964.

island (or two small islands) of Paleozoic granitic 

rocks wT as buried by basaltic breccias. The granitic 

rocks rise from sea level to a maximum altitude of 

250 m in the southern exposure and 350 m in the 

northern one. The rock is light-gray biotite granodiorite, resembling that of the batholith of Mount Northampton on the mainland to the wT est; it is perhaps part 

of the same pluton. The northern exposure displays a 

fair flow structure, sparse flat dark inclusions, and 

a few pegmatite dikes. The southern and larger exposure contains many large, irregular inclusions of 

contact-metamorphosed gneiss and is cut by many very 

irregular and discontinuous dikes of fine-grained dark 

rock.

HALLETT PENINSULA

Hallett Peninsula forms an isosceles triangle, whose 

baseline, 22 km long, trends wT est-northwTestward along 

Tucker Glacier and wThose 33-km sides intersect at Cape 

Hallett in the north (fig. 14). This is the best known 

of the peninsulas because of its easy accessibility from 

Hallett Station and because of the quality of its 

exposures. Most of the surface of the peninsula is 

hidden by an ice cap, but rock exposures are spectacular along the eastern cliffs, good along the southern 

cliffs, and fair along the northwest side.

The peninsula is a wTholly volcanic composite pile of 

breccias and lavas erupted partly from an eastern zone 

of centers near the east edge of the present peninsula 

and partly from a southwT estern zone. The constructional upper surfaces of the twT o accumulations meet 

at a swT ale that trends northward from Tucker Glacier 

to the Arneb Glacier (figs. 14,16).

EASTERN BELT

The crest of the peninsula lies along the top of the 

imposing cliff which forms the straight east side. The 

cliff rises directly from the sea at an average slope of 

60° to a height of 1,500-1,700 m along most of its 

length. (The map exaggerates the horizontal width of 

the cliff.) From the top of the cliffs, the constructional 

surface of the volcanic pile slopes gently northwestward 

to Edisto Inlet at the north and gently westward to the 

dividing swT ale at the south (fig. 14).

The rocks of the northern part of the eastern belt 

were erupted largely from a center wT ithin the present 

peninsula, but the rocks of the rest of the belt wT ere 

erupted mainly from centers east of the present crest.
C14 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA
Floating ice tongue

EXPLANATION

/5

Strike and dip of beds

X X 

Sample localities 

Boldface number, chemically 

analysed sample. Italic number, sample not analysed

10 KILOMETERS

O

169° 170°

FIGURE 14. Shaded-relief map of Hallett Peninsula and northern Daniell Peninsula, showing outcrops of volcanic rocks. Outcrops are not distinguished from ice on the mainland,

which is of Paleozoic metasedimentary and granitic rocks except where noted. Base map by U.S. Geological Survey.
C16 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

:.. .^ 1^':-tfe^-^fcS^^A^J^S

FIGURE 15. Aerial views westward over south and north ends of Hallett Peninsula. Late October, 1963. A, Cape Wheatstone. The breccias 

dipping northwestward into the peninsula were erupted from a vent since removed by erosion. The cliff at the cape is 1,200 m high. 

Tucker Glacier is on the left. B, Cape Hallett. Breccias and lavas erupted from the 1,700-m crest, left of center, dip northward to 

the cape.

Along most of the length of the peninsula, more than 

half of the eastern belt has been eroded away from 

the east. The eastern belt before this erosion must have 

resembled present Daniell Peninsula, an elongate volcanic dome.

NORTHERN VOLCANO

The only major volcano of the eastern belt that 

has an apex within the present peninsula forms a 

large dome 10 km south of Cape Hallett and 1 km 

west of the clifftop (fig. 14). The breccias and subordinate lavas of this volcano form the entire 1,600-m 

cliff directly to the east. The dip of the volcanic rocks 

decreases northward, from 15° near the volcano to 5° 

near Cape Hallett, and the crest of the peninsula 

drops correspondingly to a height of only about 200 m 

at the cape (fig. 15B). Hock units tend to thicken, down 

the dip, so that the dip decreases upward in the section. The ice-covered slope northwestward from the 

volcano to Edisto Inlet presumably also is the surface 

of the volcano.

The rocks of the volcano also dip away from it to 

the south. The dip is marked 15° low in the section; 

but the units thicken downdip, so that the dip decreases 

upward in the section, and within a few kilometers 

south of the volcano the dip of the upper units is 

subhorizontal. The general trace along the cliff of the 

layering in the breccias from here southward for 15 

km is also subhorizontal, and in these chaotic materials it was not possible to distinguish the products of 

the different volcanoes.

The cliffs on the west side of the northern volcano 

are much lower than those on the east side, are mostly 

covered by ice, and expose varied palagonitic and 

pillow breccias, lavas, and pillow lavas. The best of 

the western exposures are those around Cape Hallett, 

north from Seabee Hook and Hallett Station (fig.

19). The cliffs here, a few hundred meters high, are of 

palagonite breccias and pillow complexes, which are 

capped by several tens of meters of interlayered scoria 

and subaerial lavas.

EASTERN VOLCANOES

South of the northern volcano, the surface of the 

eastern belt rises gently to its abrupt truncation by 

the eastern cliff, so that only a part of the west slope 

of the volcanoes is preserved. All major centers which 

contributed to the present surface lay east of the 

clifftop. There were no dominant circular volcanoes: no 

radiation of flows and breccias can be inferred from 

the uniform gentle westward slope of the surface, 

from the evenness of the 1,500- to 1,700-m crest, or 

from the subhorizontal trace of bedding in the breccias exposed in the eastern cliff. Perhaps the major 

eruptions were from long fissures; or perhaps they 

were from many centers scattered along a rift zone.

The eastern cliffs expose to their crest palagonitic 

breccias and pillow breccias. Of the rare exposures 

through the ice cap on the summit surface of the 

eastern volcanic pile, however, the several visited are 

of subaerial scoria.

SOUTHEASTERN VOLCANO

The breccias of the southeastern corner of Hallett 

Peninsula dip northwestward, even at Cape Wheatstone (figs. 15A, 16), and hence were erupted from a 

volcano southeast of the present peninsula. These breccias dip beneath those of the main eastern rift belt, 

indicating that this southeastern volcano is somewhat 

older. A minor swale separates the surface of the 

northwest-dipping corner breccias from the rest of 

eastern belt.
HALLETT VOLCANIC PROVINCE C17

FIGURE 16. Aerial view northward over Hallett Peninsula. From the conical volcano of Mount Harcourt (center), lavas slope westward 

to the rugged spurs of the mainland mountains. Most of the peninsula is formed of breccias erupted from a rift zone offshore from 

the eastern crest. Cape Wheatstone, far right, is formed of breccias dipping northwestward from an offshore source. Ice-capped Adare 

Peninsula (center skyline) is 100 km beyond Mount Harcourt, which stands 1,600 m above floating Tucker Glacier. Photograph TMA 

720, F 31, no. 278, by U.S. Navy for U.S. Geological Survey, altitude 6,100 m, 4 November 1960.

SOUTHWESTERN VOLCANOES

The eastern belt of Hallett Peninsula is joined in 

the southwest to the mainland by a triangular mass of 

volcanic rocks, 15 km on a side (figs. 14, 16). From the 

highest, southeastern part of this mass rises the conspicuous conical volcano of Mount Harcourt (fig. 

18). Mount Harcourt is directly in line with the crest 

of Daniell Peninsula (fig. 10), and the southwestern 

volcanic rocks of Hallett Peninsula apparently were 

erupted mostly from the north end of the Daniell rift 

zone. The rift zone is crossed at right angles by Tucker 

Glacier, which has removed any volcanoes that erupted 

in its path.

Young Mount Harcourt volcano dominates the southwestern mass (figs. 16,18). The cone has been glacially 

eroded (presumably after breaching of a crater) back 

to its 1,600-m apex so that its structure is exposed in 

cross section. Eruptions from the volcano produced 

subaerial rocks at high levels but subglacial ones 

downdip.

Subaerial basalt lavas and cinders form the apex 

and veneer the slopes, and on the lower flanks lie unconformably upon older flows and breccias. The rocks 

of the volcano are otherwise entirely subglacial breccias. Between the all-subaerial and all-breccia sections 

is a zone of intertonguing, wherein subaerial rocks give 

way downdip to breccias (fig. 18). The transition-zone 

contact between subaerial and subglacial rocks occurs 

as high as 1,300 m, and as low as about 700 m, thus 

probably defining fluctuating levels of Tucker Glacier,

against which the rocks were erupted. The youngest 

subaerial rocks were not seen to give way to breccias 

at any altitude, hence they represent eruption at a 

time of low ice levels more like those of the present.

The breccias within the erosional embayment dip 

outward from the center of Harcourt volcano and 

hence clearly were erupted from it. To the west, dipping 

breccias give way to interbedded subhorizontal breccias 

and lavas, across whose eroded surface lap subaerial 

flows and cinders. Whether these western breccias and 

subaerial rocks were erupted from Harcourt or from 

some unidentified center is not known. The breccias 

dipping outward from the center of Harcourt volcano 

are exposed southeastward for about 4 km from the 

volcano, at which distance the top of the breccias disappears beneath ice.

Breccias from a volcano centered either south or 

southeast of Mount Harcourt are exposed in cliffs 

east of Mount Harcourt (fig. 14). These remnants of 

a vanished volcano dip eastward beneath a westwardthinning wedge of other breccias, which presumably 

were erupted from a center along the eastern crest of 

the peninsula. The wedge is in turn overlain near its 

west edge by subaerial flows and cinders whose source 

was not established.

Cliffs and bare slopes west of Arueb Glacier expose 

well the north end of the southwestern volcanic mass 

of the Hallett Peninsula. Only palagonite and pillow 

breccias are exposed below an altitude of 300 m. Above 

this breccia complex, thin subaerial lavas and scoria
CIS CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA
Breccia from southern volcan

Basalt. "' 

on rnefasandstone)

. ; -.>. ..

ormick Island

Breccia

ones (summit,300m)

Possession 

Island

Breccia . .,;»:.. '- . -,

ows over .250m 

breccias * Foyn 

Island

Cape Roget

Emperor Cliffs.GOOm 

penguin

10 KILOMETERS

O

M ?D

170° 171°
C20 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

FIGURE 18. Mount Harcourt (1,600 in), looking northward from floating Tucker Glacier. Subaerial lavas and cinders form the apex of this 

young volcano and veneer its slopes, but give way downdip to ice-contact breccias. The dashed line on the right marks the approximate intertonguing contact between subaerial and subglacial rocks. 15 November 1964.

sheets cap the cliffs and cover the upper slopes. Both 

the lower breccia complex and the upper lava series

FIGURE 19. Aerial vi«w, steeply downward to the east, of Cape 

Hallett (far left) and Seabee Hook. The hook is formed of beachworked till. Fast sea ice surrounds hook and cape. Hallett Station 

is at the near (northwest) end of the hook, and the Ad61ie penguin 

rookery occupies most of the remainder. The hook consists of 

volcanic-rock till from a glacier which came down the steep slope 

from the crest of the peninsula and was grounded in this part of 

the inlet, as now is the glacier farther right in the photograph. 

The till of the southeastern part of the hook- -the dark apron at 

the foot of the cliffs preserves its primary angular blocks and 

hummocky topography. The till of the remainder of the hook has 

been variably modified by marine erosion and deposition and by 

ice push, during a stand of sea level higher than the present one. 

The broadly arcuate north edge of the hook has been most modified 

and now consists of a beach-gravel ridge, in which the larger 

boulders commonly have a diameter of half a meter. Low ridges and 

swales extending southward from the beach ridge in the narrow 

part of the hook may be modified from recessional-moraine lines. 

The broad west end of the hook is marked by west-trending beach 

features at the north side, and by irregular low ridges and swales 

roughly concentric to the southern shore. Photograph TMA 713- 

F31, no. 110, taken 3 November 1960 by U.S. Navy for U.S. 

Geological Survey.

dip gently northward, parallel to the constructional 

upper surface of the pile. The topographically highest 

and southermost exposures are at an altitude of 450 m.

SEABEE HOOK

Seabee Hook projects 1 km westward into Edisto 

Inlet from the west side of Cape Hallett (fig. 19, this 

rept.; Harrington and others, 1967, fig. 3 and folded 

map) and is formed of beach-worked till. The hook 

rises a maximum of about 5 m above sea level.

ADARE PENINSULA

The longest (77 km) exposed volcanic pile is that 

of Adare Peninsula. From the saddle by which it is 

attached to the northeastern corner of the mainland, 

the peninsula projects far to the north-northwest and 

a shorter distance to the south-southeast (fig. 17). The 

southern half of the peninsula is about 15 km wide; 

but northward from the middle, the peninsula narrows 

to Cape Adare.

Adare Saddle marks the contact between volcanic 

rocks of the peninsula and the basement rocks of the 

mainland. The sea-level length of the saddle is only 

about 12 km. Moubray Glacier fills the trough extending south from the saddle and is grounded almost to 

Cape Roget at the south end of the peninsula, beyond 

which it projects as a floating ice tongue. Very little 

ice is grounded north of the saddle; from the saddle 

the mainland coast extends northwestward, large Robertson Bay being enclosed between mainland and 

peninsula.

SOUTHERN DOME

The southern two-thirds of the peninsula is a broad, 

elongate, ice-capped asymmetrical dome (fig. 20Z?).
HALLETT VOLCANIC PROVINCE C21

FIGURE 20. Overlapping aerial views eastward to Adare Peninsula. 

A-, The high, narrow northern part of the peninsula is separated 

from the broad shield volcano (right) by a broad saddle. Triangular 

Ridley Beach (beach and moraine) projects into Robertson Bay 

from Cape Adare (left). Length of peninsula at shoreline within 

picture is 30 km. The crest in the center of the picture is 1,400 m 

high. B, The broad shield volcano (center distance) rises 2,100 m

above the sea ice of Robertson Bay. Nameless Glacier spills from 

a breached caldera on this shield. The volcanic pile is separated 

from the folded metagraywacke mountains of the foreground and 

right center by ice-filled Adare Saddle. (Photographs TMA 715, F31, 

Nos. 228 and 238, by U.S. Navy for U.S. Geological Survey, altitude 

6,000 m, 3 November 1960.)
C22 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

The 2,000-m crest of the dome lies east of the midline 

of the peninsula. The long, smooth, gentle south slope 

of the dome is almost entirely ice covered. The north 

slope is much steeper and, facing the midday sun, is 

mantled only thinly by ice, through which project 

many outcrops and cinder cones.

The high part of the dome is a composite of at least 

four major volcanoes. The most obvious of these has a 

caldera, 6 km in diameter, breached and filled by 

Nameless Glacier (fig. 20Z?). The flanks of the caldera 

volcano are relatively steep, and rocks apparently 

erupted from it extend only about 8 km north from 

the rim and an even shorter distance to the south. 

Subaerial basalts were sampled on the high east 

rim, and trachyte of uncertain occurrence on the 

lower southwest rim. The volcano was not examined 

elsewhere.

Two major volcanoes form the crest east of NameFIGURE 21. Aerial view westward over the northern part of the main 

shield volcano of Adare Peninsula to Kobertson Bay and the mainland. The cliffs rise 2,000 m above the sea ice; the lower 1,800 m 

is of palagonitic and pillow breccias, whereas the capping darker 

200 m is of thin-bedded Subaerial lavas. One cinder cone on the left, 

and two on the right, project through the capping ice; exposures 

between them are partly of moraines. Nameless Glacier caldera 

indents the far side of the summit plateau on the left. Photograph 

TMA 712, F 31, no. 61, by U.S. Navy for U.S. Geological Survey, 

altitude 6,000 m, 3 November 1960.

less Glacier caldera, and their products cover those of 

a third volcano, whose original apex probably was 

offshore. The relations among the volcanic rocks from 

the three centers are seen in the cliffs on the east side 

of the peninsula. Breccias and pillow complexes from 

the offshore center extend almost to the 2,000-m top 

of the cliffs, where they are capped by a northwardthickening veneer of subaerial rocks from the northern 

volcano (fig. 21). Navy air photographs indicate that 

the breccias dip more gently northward than the overlying subaerial rocks and are bevelled against them; 

the subaerial rocks appear to reach sea level and are 

so indicated in figure 19. At least five cinder cones are 

exposed along the north slope of the northern volcano 

(figs. 17, 21) and indicate continuing activity along 

a crestal vent zone. All preserve circular rims and closed 

craters but show varying degrees of ice erosion. Breccias from the offshore volcano, dipping about 20° southward, are overlapped by breccias dipping gently outward from the southern volcano. Subaerial basalt and 

trachyte were collected from near the summit of the 

southern volcano, but no veneer of these rocks is apparent in photographs of the cliffs to the east. The 

surfaces of the southern, northern, and offshore volcanoes meet in a swale, from which an outlet glacier 

tumbles to the sea and supplies a grounded ice foot.

The south end of the peninsula is ice capped except 

near Cape Roget, where 600-m cliffs expose breccias 

and pillow complexes. The uppermost 50 m in some of 

these cliffs is of thinly layered dark rocks, which could 

be subaerial. The breccias dip southwesterly, hence the 

rocks probably were erupted from a source near the 

east side of the peninsula.

The smooth southwesterly slope of the southern half 

of the peninsula, little modified by erosion, is the constructional top of the volcanic pile. There is no comparable constructional slope to the east, for, from the 

divide near the east side of the peninsula, ice falls 

much more steeply to the sea. The original vent zone 

and constructional crest must have lain east of the present topographic divide, the eastern half or more of the 

volcanic edifice having been eroded away. The breccia 

platforms of McCormick Island and the Possession 

Islands presumably are remnants of the missing 

edifice. As is discussed subsequently, the Possessions 

may have formed near major vents, so they may mark 

the vent zone of an enormous volcanic structure, of 

which the southern part of Adare Peninsula preserves 

only the lower half or third of the western flank.
HALLETT VOLCANIC PROVINCE C23

NORTHERN PENINSULA

A broad, low saddle marks the beginning of the 

northern peninsula. Warning Glacier tumbles into 

Robertson Bay from the west side of the saddle 

(fig. 2(L4), but sea cliffs several hundred meters high 

bound the east side. As the crest climbs northward 

from this saddle, the peninsula narrows and the 

bounding sides rise and converge at a 1,400-meter apex. 

The crest is close to the seaward east side, where sheer 

cliffs rise several hundred meters above the water, and 

broken cliffs extend to the crest. On the bay side, the 

basal cliff is lower and the upper slopes are moderate. 

The original volcanic crest lay east of the present 

topographic crest.

Gently sloping parts of the crest near the north end 

of the peninsula are veneered by till, which is formed 

largely of local volcanic rocks. Up to an altitude of 

520 meters, however, numerous erratics of mainland 

metasandstone and metasiltstone, and a few of granitic 

rocks, were seen during an air-and-ground inspection. 

Thus, an ice sheet filling Robertson Bay and moving 

northward and eastward away from the mainland at 

one time extended to at least this altitude and may 

well have covered the entire peninsula. Till mantles 

most of the exposed surface of the broad saddle between the high central volcanic dome and the narrow 

northern peninsula, but this till was not examined and 

it is not known whether it contains mainland erratics.

The sea cliff on the west side of Cape Adare consists 

of basalt flows and a massive basalt unit of undetermined character. The northern peninsula was sampled 

only at outcrops through till at the top of the bluffs 

east of Ridley Beach. The lower of these outcrops consists of a subaerial breccia of ropy basalt fragments 

(bombs?), the upper of basalt of undetermined occurrence. Priestley (1923, p. 8-11) reported that the northern part of the peninsula is composed of interbedded 

basalt lava and subordinate breccia, dipping gently 

northward. His photographs (1923, pis. 7, 8) show 

breccias, megapillows, and agglomerate.

Priestley (1923, p. 11 and pi. 11) described a remarkable agglomerate at Cape Adare, which contains in a 

matrix of tuff abundant "foreign boulders . . . which 

both from their heterogeneity and the shape of individual boulders are undoubtedly glacierborne erratics." 

The dominant erratic type is "green quartzite," but 

schist, granitic rocks, and varied volcanic and porphyritic rocks are present also. I infer subglacial 

eruption through morainal debris at the base of an ice 

sheet extending from the mainland.

RIDLEY BEACH

Triangular Ridley Beach projects westward into

Robertson Bay from Cape Adare (figs. 20, 22, this 

rept.; see also map by Priestley, 1923, pi. 2). It conFIGUKE 22. Aerial view southward over Ridley Beach, which projects 

1 km westward into Robertson Bay from Cape Adare. The ridges 

along the near shore have been produced by beach processes, but 

the arcuate ridges subparallel to the far shore, and forming most 

of the area, may be recessional moraines. The low terrace along 

the foot of the cliffs is of protalus ramparts and of till from past 

hillside glaciers. 14 November 1964.

sists of two sets of ridges standing a few meters above 

sea level and separated by swales. One set forms concentric arcs parallel to the southwestern shore, curving 

northwestward from initial trends almost tangential to 

the peninsula. These ridges are truncated at high 

angles by the second set, which consists of less regular 

ridges along the northwest edge in a belt 150 or 200 m 

wide. The beach is composed of gravels dominated by 

volcanic rocks but containing numerous erratics from 

the mainland. Sounding and bottom sampling by 

Priestley (1923, p. 2 and pi. 2) showed that similar 

gravels extend at least TOO m to the northwest and 

500 m to the west of the exposed beach.

The concentric arcuate ridges which form most of 

the beach may be recessional moraines from an ice 

sheet that once filled Robertson Bay. All the arcuate 

ridges have been modified uniformly by beach processes and ice push along the north edge of the triangle 

(fig. 22); the arcuate ridges are older than the northern beach ridges and did not form concurrently with 

them.

McCORMICK ISLAND

McCormick Island (Cape McCormick on older 

maps) is joined to southern Adare Peninsula by 

grounded ice. The island consists of a platform of 

breccia, ringed by a sea cliff and surmounted by two
C24 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

B

FIGURE 23. Aerial views of the islands east of southern Adare 

Peninsula, 8 November 1964. A, Northward across McCormick Island. Two Holocene cinder cones lie upon a sea cliff-ringed platform of breccia. The unbreached crater contains a lake. Summit 

altitude is about 300 m. B, North-northeastward over Foyn Island 

(center) and stacks to Possession Island (distant). The high point 

of Possession Island, 200 m high, is held up by a basalt dike that 

dips toward the swale in the center of the island.

very young basalt cinder cones, one breached and the 

other not (fig. 23^4). The breccia platform could have 

been beveled by either sea or ice erosion, but the cinder 

cones have not been eroded by ice, and hence they are 

younger than all prior periods of glaciation appreciably more extensive than the glaciation of the present 

time. The northern cone was sampled and found to 

contain abundant xenoliths of white granitic rock.

POSSESSION ISLANDS

Volcanic remnants form the small Possession Islands, east of southern Adare Peninsula (figs. 17, 

23Z>). Four islands and four stacks form a group 10 

km long in a northerly direction and 3 km wide. All 

the islands are ringed by sea cliffs. The two main 

islands, Possession and Foyn (fig. 23Z>), bear permanent snowfields, but none of the islands has an ice cap. 

The rocks that were seen are entirely basaltic. Names

of the individual islands have been used inconsistently; 

the convention followed here is that of the Northeastern Victoria Land Sketch Map of the U.S. Geological 

Survey.

Possession Island is the northernmost of the group 

and, with a diameter of about 2.5 km, is also the 

largest. A prominent rib trends along the west side of 

the island to form its 200-m crest, from which cliffs 

fall directly to the sea. The rib is formed by a dike of 

basalt, about 50 m thick, that dips 35° eastward and is 

well exposed in the sea cliffs; the east slope of the rib 

is the stripped upper surface of the dike. Beneath the 

dike (or perhaps part of it) is a megapillow complex 

(fig. 30Z>). A sharp low swale separates the rugged 

western third of the island from a rolling platform, 

formed of nearly horizontal basalts, that rises gently 

eastward to the top of sea cliffs 60-100 m high.

Foyn Island (fig. 23Z>) is an uneven platform 2 km 

in diameter that rises to a 250-m peak at the north 

end. The high northern sea cliffs expose basaltic 

breccias, pillow complexes, and a megapillow (fig. 

306y ). The surface of the island where examined in its 

southern part is formed of apparently subaerial basalt 

 mostly dense lava and partly scoriaceous lava. Small 

cinders are abundant, and a large pile of them may 

represent an ice-eroded cinder cone, but other than this 

possible cone no vents for either flows or cinders were 

recognized.

No landings were made on Heftye Island (fig. WA) 

or on the small unnamed southern island of the Possession group, but telephotographs taken from Foyn 

Island show their structure clearly. Both islands consist of breccias and megapillow complexes. Heftye has 

a rolling surface from which vertical cliffs fall 60-80 

m to the sea, whereas its unnamed neighbor has a 

rugged summit of about 250 m.

Possession, Foyn, and Heftye Islands have rolling 

surfaces, and the basaltic rubble that covers most of 

the surfaces of at least Possession and Foyn has been 

much redistributed by ice. No mainland erratics were 

'noted. Whether the ice consisted of local caps or was 

part of a large Ross Sea ice sheet is unknown. As no 

elevated beaches or raised sea cliffs were recognized, 

marine planation is not called upon to explain the 

rolling erosion surfaces.

The Possession Islands expose in general much more 

massive rocks than do any of the large coastal volcanic 

piles. Palagonite breccias and thin flow units, which 

dominate all the coastal complexes, are a minor component of the islands, whereas massive megapillows, 

at least 50 m in diameter, are conspicuous on the 

islands (fig. 30). The islands presumably owe their 

preservation to the resistance of these massive rocks
HALLETT VOLCANIC PROVINCE C25

to erosion, any surrounding palagonitic and thinly 

layered complexes having been eroded away.

The Possession Islands may mark the vent region 

of an old pile of breccias like those of the large 

coastal accumulations. The massive megapillows perhaps formed near the source, and the breccias away 

from it. The northerly alinement of the islands is the 

general direction to be expected for a vent zone in 

this region.

AGE OF VOLCANIC ROCKS

The volcanic rocks of the Hallett province are of 

very late Miocene, Pliocene, and Quaternary age, and 

all major volcanic piles are still active. Table 1 presents potassium-argon whole-rock determinations of 

the age of basalt samples as analyzed by Kichard Lee 

Armstrong (written commun., 1968) of Yale University. The general reliability of such whole-rock determinations of age of unaltered basalts is demonstrated 

by the concordance between determinations from separated minerals and those from whole rocks (Burke 

and others, 1969).

Three of the dated samples are from topographically 

and structurally low positions in the volcanic piles of 

Coulman Island and Hallett Peninsula and are of 

latest Miocene and early Pliocene 1 ages 7.3, 6.6, and 

5.4 m.y. (million years). The volcanoes rise from a 

continental shelf 300-600 m deep; this depth is small 

relative to the 1,500- to 2,000-m altitudes of the crests, 

so presumably volcanism began within very late Miocene time.

The fourth sample is from the south end of Adare 

Peninsula and has an age of 2.6 m.y. late Pliocene, 

if we accept the age of 1.8 m.y. favored by Bandy and 

Wilcoxon (1970), Kennett, TVatkins, and Vella (1971), 

and others for the Pliocene-Pleistocene boundary. The 

sample is from the base of the 600-m cliffs at Cape 

Roget. This represents middle rather than basal levels 

in the exposed volcanic structure: older rocks are exposed in the much higher cliffs farther north. The 

lower part of the Adare volcanic pile must be of Miocene or early Pliocene age.

The volcanic structures of Coulman Island and 

Hallett and Adare Peninsulas thus have been built

1 In these designations, I am following the time scale of Berggren 

(1969), which places the Miocene-Pliocene boundary at about 6 m.y.; 

see also Chariot and others (1967). This age is thought to be that of 

the boundary between the Epochs as denned by marine invertebrates 

in the Mediterranean region, although ambiguities permit a boundary 

within the range 5.5-7 m.y. The 12 m.y. age of the boundary established in North America between the Barstovian and Clarendonian 

vertebrate stages, long assumed to be late Miocene and early Pliocene, respectively, apparently is much older than the type European 

Miocene-Pliocene boundary.

TABLE 1. Potassium-argon dates from whole-rock samples of 

basalt low in the volcanic piles of the Hallett province

[Analyses by Richard Lee Armstrong, Yale University, 1968. Constants used for calculations of dates: Kj^g, 4.72 x-10-10 year; 

KXe , 0.584X10-10 year; K40/K, 0.0119 atom percent. Sample localities 

are shown on figures 6, 14, and 19. Radiogenic argon calculated 

at standard temperature and pressure]

Field 

No.

Type of 

volcanic rock

Radiogenic Ar«x

Cm3g-l

Air 

correction

(per- Potassium 

cent) (percent)

Age 

(106 years)

220C Pillow in palagonite 

breccia, west side 

Coulman Island __ 0.609 85 2.09, 2.10

247G Massive basalt,

grades into palagonite breccia, east 

side Hallett Peninsula __________

249B Pillow in palagonite 

breccia, Cape 

Wheatstone, Hallett Peninsula ___

233D Pillow in palagonite 

breccia, Cape 

Roget, Adare

Peninsula. ____ .072, 95 0.732, 0.717, 

.078 96 0.726

.277 82 1.04, 1.06

.448 55 2.07, 2.08

7.3 ±0.48

6.6 + 0.37

5.40±0.15

2.60 + 0.4

during the same late Miocene to Holocene time span 

insofar as their ages can be defined.

BATHYMETRY

The volcanic peninsulas and Coulman Island rise 

from a continental shelf which has a depth of mostly 

between 300 and 600 m (fig. 24). At the north end of 

the Ross Sea, the shelf break is at about 500 m, the 

continental slope trends northwestward, and the ocean 

floor at its foot has a general depth of about 2,200 m. 

The relatively deep shelf break is characteristic of 

Antarctica and is generally attributed to isostatic depression of the continent under the load of its ice cap.

The Adare Peninsula volcanic field appears from 

the submarine topography to extend far to the southeast, east, and north from the exposed peninsula: 

volcanism has extended the continental slope northeastward by building upon it. The northward underwater projection of the peninsula continues to the edge 

of the continental slope. East of the peninsula, the 

continental slope trends northward, perhaps there also 

expanded by volcanism. The 400-m isobath may 

roughly outline the volcanic pile and if so the volcanic 

axis trends north-northwestward, passing through the 

Possession Islands and near the east side of the exposed 

peninsula.

The 400-m isobath lies close to the southern ends of 

both Daniell and Hallett Peninsulas, but swings far
C26 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

71°S

are Penlnsuia: \

.... _^'_ \ ;

£ . OS

U i f V

73

FIGURE 24. Bathymetric map of the northwestern Ross Sea. Contours in meters ; dashed where control poor. The major exposed 

volcanic piles are marked by a pattern. The coastline shown is the subice shoreline as interpreted beneath grounded ice where 

present. Contoured from soundings reported on U.S. Navy Hydrographic Office Charts 6626 (1962), 6627 (1966). 6628 

(1966), 6636 (1966), 6663 (1959), and 6665 (1963).
SALLETT VOLCANIC PROVINCE 027

eastward from central Daniell and from northern 

Hallett without obvious relation to known and inferred vent zones. Coulman Island is closely surrounded by deep water, and depths between it and the 

mainland exceed 600 m. There is no suggestion in the 

bathymetry that any underwater volcanic pile connects the island with Daniell or Hallett Peninsulas. 

Nor does a submarine ridge connect Adare and Hallett 

Peninsulas to suggest continuity of volcanism between 

them; on the contrary, the peninsulas are separated 

by a west-trending submarine low, which has a depth 

of more than 600 m. Erosion by an enlarged Ironside 

Glacier is inferred.

THE BRECCIAS

Each of the offshore volcanic piles largely consists 

of breccias and lavas apparently formed by eruptions 

beneath ice sheets and melt-water lakes. The chaotic 

varicolored volcanic complexes are exposed spectacularly in cliffs that reach heights of 2,000 m. Many of 

the rock characteristics are shown in the photographs 

(figs. 25-30) and are described by the photograph 

captions.

The complexes consist mostly of irregularly anastomosing layers and lenses, or marble-cake chaoses, of 

nodular basalt in palagonite breccia, and include minor 

amounts of bedded palagonite tuff. Dikes, sills, and 

megapillows intrude these complexes, which are interpreted to have formed in contact with ice and melt 

water. More evenly layered units of lava flows and 

reddish scoria and breccias also occur.

The paucity of throughgoing bedding markers and 

the complicated lateral and vertical gradations and 

mixing of contrasted rock types apparently indicate 

that thick sections formed during single episodes of 

continuous volcanism. Figure 265 illustrates a 400-m 

section formed mostly of two volcanic-episode units. 

The upper 200 m of figure 26J. represents one unit. 

The only obvious break in the section of figure 26C 

occurs at a height of about 250 m in the 600-m section. 

Still thicker units can be inferred in much higher 

cliffs such as those of figure 25. The clear definition of 

volcanic-episode units of Daniell Peninsula illustrated 

by figure 29J. is exceptional.

PALAGONITE BRECCIA

Palagonite breccia consists of clasts, nodules, and 

granules of basalt in a palagonitic matrix. The lightcolored breccia occurs primarily as lenses intercalated, 

interfingered, and anastomosed with dark nodular 

flows and pods of basalt to form thick composite units. 

This section describes the breccia component of these 

units. The amount of breccia in the composite units is 

generally between 20 and 70 percent, but the content

drops to 5-10 percent in some units, in which it adds 

an irregularly striped or marble-cake appearance to 

the otherwise relatively massive basalt, or discontinuously separates thin pods or lenses of lava (figs. 26, 

27, 28, 29).

The breccia lenses are mostly yellowish or brownish 

gray and range in thickness from less than 1 m to 

more than 50 m. Throughgoing bedding planes, separating composite units, are commonly hundreds of 

meters apart. The units separated by such discontinuities consist of breccia and lava intertongued at all 

levels; each unit consists of two rock types that 

formed simultaneously and accumulated without 

major break in volcanism.

Basalt clasts vary greatly in size within single 

lenses, typically from 1 cm (centimeter) to 1 m in 

maximum dimension, but reaching 10 m. Varying 

concentrations and sizes of clasts define obscure, discontinuous bedding within breccia lenses (fig. 27A).

Clasts vary widely in texture and appearance. They 

are dense to richly vesicular, the vesicles being either 

empty or lined with secondary minerals but not commonly filled (figs. 275, C). Concentric rims of vesicular basalt on blocks of more dense basalt (figs. 275, 

C) demonstrate that fragmentation and fluid eruption 

overlapped in time. Clasts, like the rock of the lenticular flows intercalated with the breccias, are of gray 

not reddish and oxidized basalt.

Fragmentation of the lenses and pods of nodular 

basalt to produce clasts like those in the breccia is apparent along most contacts between breccia and lava 

(figs. 277?, E). The nodular lavas are closely jointed, 

and many parts of them are fractured to granule size; 

the lavas grade into breccias as their marginal 

fracture-bounded chunks become separated and the 

interstices are filled by granules of palagonite and of 

varied basalt. The breccias are the most fragmented 

parts of the lava flows.

Clastic dikes of palagonite breccia and palagonite 

tuff cut through the breccia sequences and have exposed heights of hundreds of meters in many places. 

Some, like those of the east side of Coulman Island 

(fig. 26£7), are as thick as several tens of meters. The 

abundance of these clastic dikes emphasizes the mobile 

character (due to water lubrication and "slippery" 

mineralogy ?) of the tuffs and breccias during the volcanic episodes.

PALAGONITE TUFF

The brightest colors of the volcanic piles, the yellows and subordinate reds and oranges, are provided 

by the palagonite tuffs. The tuffs are bedded to massive and occur as large masses of relatively pure tuff,
C28 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

FIGURE 25. Breccias of east side of Hallett

A, Palagonite breccia, nodular lavas, and subordinate amounts of palagonite tuff, with varying dips due to superposition of products 

from s.everal vent areas. Note the paucity of throughgoing bedding planes. Center of peninsula.
HALLETT VOLCANIC PROVINCE C29

B

Peninsula, exposed in cliffs 1,400-1,500 m high.

B, Palagonite breccia, nodular lavas, and palagonite tuff. No bedding plane can be traced with confidence across the picture. The wellbedded lavas of the lower left, for example, merge right of center with marble-cake breccia and lava which grades upward into 

interlayered breccia and lava. Twelve km north of Cape Wheatstone.
C30 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

B
HALLETT VOLCANIC PROVINCE C31

il

FIGURE 26. Breccias of Coulman Island. A, Palagonite breccia (light) 

and nodular lava (dark). West side of Coulman Island; locality 

220 is just to the right of the illustrated area. The foreground 

cliff is 350 m high, the background peak 800. Se« figs. 29C and 

29.D for closer views of parts of the section. B, Palagonite breccia 

(light) and nodular lava (dark). The upper half of the section 

consists of chaotically jumbled palagonite breccia, and pods and 

irregular masses of lava, and encloses large autoliths of lightcolored palagonite tuff. Below this is a thin section of well-bedded 

breccia and nodular lava. These intertongue downward in a thin 

zone (mostly out of the picture area to the left) with lenticularly 

bedded breccias and lavas which extend to the base of the exposure,

and are striped by palagonite tuff. Within this lower sequence, 

only the thickest and lowest bed of light tuff can be traced across 

the exposure well beyond the photographed area, all other units 

anastomosing or lensing out. The section is interpreted to have 

formed during three eruptive episodes, the conspicuous light tuff 

and the top of the thinly layered rocks marking the contacts between the eruptive units. North end of Coulman Island, locality 

216; the cliff is 400 m high. C, Marble-cake palagonite breccias 

and irregular lavas, cut by clastic dikes of palagonite tuff. Note 

the lack of continuity of bedding in most of the exposure. Cliff 

600 m high, near center of east side of island.
C32 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

A

D

E

FIGURE 27. Palagonlte breccia, base of cliffs at west side of central 

part of Coulman Island, locality 220. 7 November 1964. A, Rudely 

bedded breccia containing fragments and spheroids of basalt in a 

soft palagonltlc matrix. B, Closer view of part of same outcrop, 

showing basalt clasts which are variously dense, vesicular, and 

scorlaceous. Two spheroids, one above the center and one at bottom 

center, have concentric structure. C, Close view of another spheroid 

in outcrop shown in A. A block of vesicular basalt Is rimmed by 

a shell of more dense basalt containing small partly filled vesicles. 

D, Breccia containing a large block (left) of much-fractured dense 

basalt, fragmentation of which provided clasts for the breccia. E, 

Closer view of the same outcrop, showing gradation (across center 

of picture) from fractured basalt to separated clasts.
HALLETT VOLCANIC PROVINCE C33

as the finer grained parts or beds in palagonite breccias, and as inclusions in basalt flows.

The tuffs consist of sand- and granule-sized fragments of glassy basalt and palagonite in a soft, porous, 

earthy palagonitic matrix. The small clasts sho\v varying palagonitization, being mostly fresh in some tuffs, 

\vholly palagonitized in some, and marginally altered 

in others. Adjacent clasts can vary widely in degree of 

palagonitization. Crystal fragments form minor clasts. 

Color boundaries cross bedding layers (figs. 2&4, B, 

C), indicating that postdepositional processes have 

caused variations in the oxidation, hydration, and 

concentration of iron.

Much of the palagonite tuff is bedded and forms 

water-laid horizontal and inclined sheets, cones, and 

fragments of cones, deposited on and covered by breccias and lavas. Relatively even and subhorizontal units 

of bedded tuff (fig. 28/7) are uncommon.

The bedded palagonite tuff occurs primarily as 

abundant lenses and cones intercalated in, and intertonguing with, complexes of palagonite breccia and 

nodular basalt. Irregular lenses of palagonite tuff are 

visible as the light-colored rocks in breccia complexes 

in figures 26-6 and 28F. The largest masses of bedded 

palagonite tuff occur as cones, 100-300 m high (figs. 

28A, B, C, D). The cones are truncated at the top and 

cut a\vay by erosion, presumably by subaqueous slumping, bulldozing by lavas and intrusions, and cutting 

by water currents set up by nearby hot lava. Internal 

erosional unconformities are common.

The tuff cones are all buried by, and interfingered 

downward with, palagonite breccias and nodular lavas 

(figs. 28A, D, E), showing that magmatism was synchronous with subaqueous deposition of the tuff beds. 

The beds in the cones dip at angles up to 35° a\vay 

from masses of breccia and lava, demonstrating that 

these masses had steep sides and \vere at least as high 

as the 300-m height of the taller cones. Eruptions built 

steep-sided masses, do\vn which cascaded lavas and 

palagonitic tuffs and breccias. It is inferred that the 

steep-sided masses were table mountains which filled 

cylindrical caverns melted upward into the ice sheet 

by volcanic heat, and that the tuff cones \vere formed 

in the surrounding melt water \vhen melting widened 

the hole about the table mountain.

Masses of palagonite tuff form contorted inclusions 

from a few centimeters to a hundred meters or more 

in diameter in thick lava flows. At least some of the 

inclusions were formed by the incorporation of masses 

of tuff from the cones into the lavas. Tuffs and lavas 

obviously were mobile simultaneously. Figures 28#, 

F, and G illustrate stages in the formation of tuff 

autoliths.

PALAGONITE

The term "palagonite" has two meanings, one specific and mineralogic, the other general and lithologic. 

The mineralogic meaning is that of a nearly isotropic 

mineraloid formed by the hydration of basaltic glass 

(sideromelane). The lithologic meaning, \vhich is that 

primarily employed in this paper, is that of a soft, 

brown or yello\v material derived largely by the 

hydration and alteration of basaltic glass but including clay, zeolite, carbonate, and other secondary minerals in addition to the mineraloid palagonite. A 

detailed study by X-ray and other laboratory methods 

of these secondary minerals in the Hallett volcanics 

would shed light on the important problems regarding 

the temperature and time of alteration, but no such 

study is attempted here.

The mineraloid palagonite can form by wret-tropical 

weathering of basaltic glass (Hay and lijima, 1968) 

and by slow hydration of sea-floor lava at a rate of 

something like 1 mm per million years (Moore, 1966). 

Bonatti (1965) argued that such low-temperature 

hydration is subordinate to rapid hydration at high 

temperature during subaqueous eruption, but his conclusion is disputed by others.

An explanation by high temperature seems more 

likely to apply to the Hallett rocks than does one by 

low temperature. Permafrost must severely retard 

hydration in the Antarctic. In the Hallett province, 

there is no apparent increase in degree of hydration 

with increasing age. Thus, tuffs from the north tip of 

Cape Hallett, stratigraphically high in the Hallett 

Peninsula section, and from Cape Roget, high in the 

A dare Peninsula section and dated as about 2.6 m.y. 

old, are as palagonitic as the tuffs from the oldest 

parts of the various volcanic piles. And on the other 

hand, some of the oldest tuffs examined contain basaltglass sand and granules showing almost no palagonitization. The alteration in the Hallett province 

involves the formation of various secondary minerals, 

but detailed information regarding them is lacking.

NODULAR LAVAS

Pods, lenses, and sheets of nodular lava form most 

of the nonbreccia component of the breccia complexes. 

These nodular lavas are illustrated by figure 29 and by 

many of the preceding photographs in this report. 

The nodular lavas occur primarily as anastomosing 

lenses a few meters thick. Many are evenly interlayered with breccia, whereas many others are in 

chaotic complexes of contorted, broken lava masses in 

breccia.

The pods of lava approach pillow shapes, but welldeveloped small pillows in piles of nested spheroids
C34 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA
HALLETT VOLCANIC PROVINCE C35

FIGURE 28. Occurrences of palagonlte tuff. A-D, cones of bedded 

tuff; E-F, intermediate stages in formation of large autoliths of 

tuff; G, autolith; H, subhorizontal bedded tuff. A, Two cones of 

tuff, with apexes in center and at right edge of picture, overlain 

by, and intertonguing downward to the left with, nodular basalt 

and palagonite breccia. The exposure is about 400 meters high; 

sea level is at the base. Hallett Peninsula, 11 km north of Cape 

Wheatstone. B, Closer view of the right-hand cone in A. A basalt 

dike cuts into, but not through, this cone from the right. C, Gently 

dipping nodular basalt and palagonite breccia (lower left) and 

nodular basalt and scoria (upper left) lap onto bedded palagonite 

tuff, which dips moderately left in the lower-right third of the 

picture. The tuff is partly yellow (photographs light) and partly 

moderate red (photographs dark), the color boundary cutting across 

bedding. An irregular basalt dike cuts steeply through the section 

on the right. The exposure is about 200 m high, the base being 

near sea level. Daniell Peninsula, 9 km northeast of Cape Phillips. 

D, Eroded right limb of a cone interflngering downdip with nodular basalt, which laps onto the depositional right side and eroded 

left side of the tuff mass. The exposure is 200 m high, and the 

altitude of its base is 300 m. Hallett Peninsula, 8 km north of Cape 

Wheatstone. E, Light-colored palagonite tuff in very irregular contact with dark basalt on the right, and interflngered with nodular 

basalt on the left. Nodular basalt lava underlies and overlies the 

tuff. The extremely irregular contact on the right is interpreted 

to indicate that the tuff accumulated simultaneously with the 

swelling of basalt pods. The exposure is several hundred meters 

high, and its base is several hundred meters above sea level. East 

side of central part of Coulman Island. F, Bedded tuff (light colored) has an upward protrusion (center) that contains basalt 

masses. The accumulation of tuff and the formation of basalt apparently were contemporaneous. Height of exposure, 200 m, base 

near sea level. Hallett Peninsula, 8 km north of Cape Wheatstone. G, Irregular mass of light-colored tuff enclosed in basalt, and 

in turn enclosing contorted masses of basalt with chilled margins. 

It is inferred that tuff from a bedded cone was engulfed in and 

carried along by a very thick lava flow, some of the lava from 

which was mixed into the churning tuff while still molten. Height 

of exposure 50 m, base near sea level. Hallett Peninsula, 11 km 

south of Cape Hallett. H, A thick bed of palagonite tuff, high in a 

section of breccias and nodular lavas, contains lava lenses. The 

cliff rises about 400 m above the sea ice. Daniell Peninsula, 8 km 

northeast of Cape Phillips.

were nowhere seen. Many clasts in the breccias display 

concentric structures (figs. 275, C) and hence must 

have hardened slowly in a hot environment after detachment from larger masses of partly molten lava. 

Breccias that, contain such detached pillow7 clasts are 

referred to as pillow breccias.

There is no clear distinction between lava pods and 

breccia clasts where irregular pods and lenses of lava 

occur in breccia. Pods are intricately fractured, and 

their margins display arrested stages in the breaking 

awray of clasts into the breccia (fig. 27Z>). Contorted 

lava lenses within the palagonite breccia tend to be 

thoroughly fragmented (fig. 29Z>). Apparently the 

breccias were mobile, and a churning produced many 

of the clasts by breaking up lava masses.

The nodular lavas of layers and pods in many 

places display chilled margins (fig. 295), but more 

commonly do not. Presumably the lack of chilled margins indicates that the breccias generally wrere hot at 

the time the lavas formed. This accords wdth the 

conclusion that palagonitization was the result of

high-temperature hydration, not of low-temperature 

weathering.

Many cliff sections in all the volcanic piles display 

breccia-and-lava units that appear to be products of 

single eruptions. Each unit consists of a lower chaotic 

breccia which grades or intertongues upward into 

intercalated nodular lavas and reddish breccias and 

scoria. A series of five such units is exposed in the 

east-central part of Daniell Peninsula (figs. 29^4, 

28(7). The lower part of each unit consists of massive 

or marble-cake lava and dark breccia, marked by irregular seams of yellowish-gray palagonite tuff. The 

upper part consists of lenses (either thin and regular 

or thick and contorted) of light-colored nodular lava, 

interlayered with palagonite tuff low in this part of 

the unit but interlayered with red breccia and scoria 

high in it. The iron-oxide coloring of the red scoria is 

generally superficial rather than pervasive. Nearby to 

the south, these five rhythmic units give way, by way 

of intertonguing, variable dips, and gradational and 

abrupt transitions, to the common chaotic assemblage 

of breccias, lavas, and tuffs (fig. 28/7).

Similar units consisting of lower chaotic breccias 

and upper nodular lavas and reddish breccias and 

scoria were seen in many other exposures (figs. 265, 

29#). Only at the Daniell Peninsula locality, however, 

was there found a series of clearly defined rhythmic 

units; many cliff sections display no such units at all, 

but only the more chaotic breccias.

The reddish scoria and relatively even layering of 

the upper parts of these units cannot be taken as evidence that this part formed subaerially, above the 

level of surrounding water or ice. The levels of transition from lower to upper parts are stratigraphic, not 

horizontal, and dip with the units. The cyclic units 

give way laterally to the usual breccia chaoses: the 

upper well-layered parts do not continue far laterally. 

Each unit shows an upward progression similar to 

that of the adjacent units, and an explanation based 

on water level would have to postulate that water 

depth changed between eruptions by just the amount 

needed to place the surface halfw^ay up the potential 

thickness of the products of the next eruption to come.

The reddish breccia and scoria have hardened under 

oxidizing conditions. Such oxidation can be accomplished in air or steam but probably not in liquid 

water. Oxidation by air is improbable for the reasons 

just noted; oxidation by steam of lava erupted beneath 

ice is inferred. (That ice several kilometers thick was 

present in this region during much of late Miocene, 

Pliocene, and Quaternary time is indicated by the 

character of the breccias, by the occurrence of mainland erratics on northern Adare Peninsula, and by the
C36 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

FIGURE 29. Nodular lavas in the breccia piles. A, Rhythmic brecciaand-lava units. Units (separated by lines at right edge of picture) 

each about 100 m thick consist of lower zones of contorted lenses 

of breccia and lava and upper zones of long, thin lenses of reddish 

(dark on the photograph) breccia and scoria and light-colored lava. 

Each composite unit presumably represents an episode of continuous 

volcanism. Figure 28C shows a closer view of the lowest of these 

units in a nearby section. Daniell Peninsula near locality 277. B, 

Block of breccia (light) surrounded by pods of vesicular basalt. 

Selvages of black basaltic glass about 1.5 cm thick mark contacts 

between pods and breccia, and between adjacent pods. The exposure 

is about 1 m wide. East side of Hallett Peninsula, locality 247. 

C, Intertonguing, relatively well bedded palagonite breccia (light) 

and nodular lava (dark). This is a 50-m section in the top-center 

part of the Coulman Island cliff of figure 26A. D, Marble-cake 

contorted lenses of lava and palagonite breccia. The contortions 

appear to be primarily flow folds rather than irregular intrusions.

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This is a 50-m section in the central part of the Coulman Island 

cliff of figure 26A. E, Vertical dike and horizontal lenses of lightcolored nodular lava in dark palagonite breccia. The exposure is 

about 30 m high and is midway up the cliff at the north end of 

Hallett Peninsula, and it represents the upper part of a lava-andbreccia unit.
HALLETT VOLCANIC PROVINCE C37

glacial topography of the mainland matters discussed 

elsewhere in this report.) It is postulated that eruptions beneath the ice melted a vault that did not, 

within the time span represented by the rhythmic 

breccia-and-lava units, extend to the surface. Einarsson (1966) argued on physical grounds that such limitation of melting to a basal vault should characterize 

many subice eruptions. Early eruption products were 

in contact with ice and with liquid water, and they 

formed the breccias of the lower part of each unit. 

Later in each cycle, a void over the lake in the vault 

was filled with steam, which oxidized the fragmental 

eruption products and allowed the fluid lava to spread 

out into thin flows instead of quenching it in pods and 

breccia.

MEGAPILLOWS

Large, ellipsoidal, concentrically structured masses 

of basalt occur in the breccia piles and are referred to 

here as megapillows. Particularly well developed 

megapillows were noted at the north end of Coulman 

Island and on Possession, Foyn, and Heftye Islands 

of the Possession group (fig. 30). Megapillows less 

well exposed were seen elsewhere about Coulman Island and at several places along the cliffs bounding 

Daniell and Hallett Peninsulas.

The megapillows are irregular ellipsoids of concentrically structured basalt. They typically show an 

inward progression from irregularly jointed basalt 

through small radial columns to large radial columns 

(fig. SOf), with or without a core of concentrically 

jointed basalt (fig. 30Z?). Shapes vary from subspherical (fig. 30Z?) to flat ellipsoidal (fig. 30f) and may 

be highly irregular. Thicknesses (or diameters) reach 

at least 150 m (figs. 30Z?, C). The megapillows form 

parts of thick units of breccias and nodular lavas, and 

appear to be intrusive into these units where wellexposed contacts were seen.

The concentration of megapillows in the exposures 

of the small Possession Islands is interpreted, as discussed previously, to be due partly to the resistance to 

erosion of these masses. The islands are interpreted 

to be near the vent region of an initially very large 

volcanic pile: the greater fluidity of lava near the 

vents, and the smaller proportion of breccia within it, 

may have facilitated the formation of megapillows. It 

will be recalled that the Possession Islands lie near 

the center of a broad submarine high of which Adare 

Peninsula is the exposed western one-quarter. Only a 

few megapillows were seen away from the Possession 

Islands.

The megapillows appear similar to those illustrated 

by Snyder and Fraser (1963, fig. 5) in a sill that intruded semiconsolidated volcanic mud in the submarine 

complex of Unalaska Island in the Aleutian arc.

The Antarctic megapillows apparently formed, 

simultaneously with the breccias they intrude, from 

large masses of lava that swelled within the unconsolidated and mobile breccias. The megapillows are parts 

of the breccia complexes, not unrelated younger 

intrusions.

THE BRECCIAS AND GLACIATION

The breccias are inferred to have formed largely by 

eruption of lava beneath a continental ice sheet that 

lay on the Koss Sea continental shelf during most 

of late Miocene, Pliocene, and Quaternary time. 

Grounded ice on the shelf far beyond present limits 

can be demonstrated by geologic data independent of 

arguments regarding the origin of the breccias.

PRIOR ICE LEVELS

The mainland valley glaciers of northeastern Victoria Land now all reach the sea, but the valleys display hanging tributary valleys, glacially overridden 

topography, and upper limits of valley-side planation 

and oversteepening far above present ice levels. The 

upper limit of altitude of these features decreases toward the coast, but the relative altitude above present 

ice increases: the inland level of the continental ice 

sheet was little higher than the present level. Near the 

coast, main-valley ice levels 1,100-1,200 m above present ice levels are shown clearly by well-preserved 

features of glacial erosion; older, subdued, and more 

ambiguous features suggest levels at least an additional few hundred meters higher. Projection of 

standard Antarctic ice profiles (see fig. 31 and following discussion) to the 1,200-m level requires grounded 

ice to have extended at least 50 km into the Ross Sea 

beyond the present coastline.

Past glaciations high above present levels characterize the valleys of Victoria Land along the rest of the 

Ross Sea to the south of this region also (fig. 2). In 

Taylor Valley in the McMurdo Sound region, for 

example, till is widespread up to 1,000 m above the 

floor, now ice free, of the valley (Pewe, 1960), and 

valley-glacier sculpture extends to at least 1,500 m 

above the floor (Armstrong and others, 1968). Mainland erratics have been found as high as altitudes of 

600 m on Ross Island and on the 200-meter crest of 

Beaufort Island (Harrington, 1963).

Cape Adare lies 30 km northeast of the present limit 

of grounded ice along the mainland coast of Robertson
C38 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

B

Bay (fig. 17) and, as noted previously, mainland erratics occur as high as 520 m above sea level on the 

Cape. As also noted previously, an older glaciation 

beyond Cape Adare is indicated by Priestley's finding 

of glacial erratics within volcanic breccia in the Cape 

section. Figure 31 illustrates maximum and minimum 

ice profiles which can account for the high erratics.

FIGURE 30. Megapillows of the Possession Islands. A, North face of 

Heftye Island. Irregularly interswirled scoria, breccia, and lava 

on the left give way to irregular megapillows on the right. The 

summit is about 80 m high. B, Basalt megapillow at the southwest 

end of Possession Island. Concentric zones define a semicircle on 

the left that is part of a megapillow whose left half has been 

eroded away. The outer zone is massive and dark, the intermediate 

one is radial-jointed and dark, and the large core is irregularly 

jointed and light colored. The top part of a smaller megapillow,

- not obvious on the photograph, forms the lower half of the central 

part of the picture area; dark breccia lies above and to the right 

of the two megapillows. Locality 226; the cliff is about 150 m 

high. C, Megapillow at the northwest end of Foyn Island. Concentric zones of varying types of radial-jointed basalt define a long 

pod that thickens gradually to the left across the entire picture 

area. The megapillow is intrusive into palagonite breccia around 

the corner to the left. The cliff is about 150 m high.
HALLETT VOLCANIC PROVINCE C39

sw Adare Peninsula NE

+ 2

LU +1

O

^ SEA

t LEVEL HMainland mountains

Range of possible ice surfaces at time 

of glaciation of Cape Adare

o 

-2

FIGURE 31. Schematic profile across Robertson Bay, Cape Adare, and the continental shelf, showing ice levels at the time the continental 

ice sheet overrode Cape Adare. The ice-cap profile (shown in maximum and minimum positions) is that now typical of the Antarctic ice 

sheet (Bakayev, 1966, pis. 21, 22). Isostatic depression due to more extensive glaciation is not included but would increase maximum 

ice thickness above Cape Adare by several hundred meters. Vertical exaggeration X 10.

If the erratics were carried on the top of the ice sheet 

from whicji they were melted, then projection of 

standard ice-sheet profiles, disregarding isostatic altitude changes, indicates that the ice sheet extended 

about 15 km north of Cape Adare and that it stood 

about 800-1,000 m above present ice levels at the mainland margin of Robertson Bay. It is of course unlikely 

that the erratics were at the top of the ice sheet. The 

outer limit for grounded ice is provided by the shelf 

break, which is only about 15 km beyond the minimum 

limit of the ice. Projection of a standard profile from 

the shelf break provides about 300-400 m more ice 

at Cape Adare and perhaps 200 m more at the mainland coast (fig. 31). Adding the allowance for isostatic 

depression of Robertson Bay and the continental shelf 

by the load of the expanded ice sheet into these calculations increases the thickness of ice that is permitted at Cape Adare by the shelf-break limitation by 

something like 300 m, or to a height of about 1,200 m 

above present sea level.

The central Adare Peninsula breccias inferred to be 

of ice-contact origin to the present altitude of 1,800 m 

are 40-50 km from the shelf break (fig. 24). Projection of a standard ice profile (fig. 31) from the shelf 

break would put ice to 1,000-1,200 m above sea level

at east-central Adare Peninsula, and to this height 

should be added approximately 500 m for isostatic 

depression of the continental shelf. This gives a total 

of about 1,600 meters of ice above present sea level. 

This calculation, using uncertain variables, thus yields 

an ice thickness about the same as that inferred from 

the upper limit of the breccias.

ICE-CONTACT BRECCIAS OF ICELAND

Palagonite breccia complexes strikingly like those 

of the Hallett province were produced in Iceland by 

eruptions beneath Quaternary ice caps. These basaltic 

complexes form about an eighth of the surface of Iceland and have been described and interpreted by various geologists, including Einarsson (1966), Jones 

(1969a, b, 1970), Kjartansson (1967), Noe-Nygaard 

(1940), Peacock (1926), van Bemmelen and Rutten 

(1955), and Walker and Blake (1966).

The most distinctive occurrences are in steep-sided 

table mountains, which consist largely of piles of massive to thinly interbedded palagonite breccia and tuff. 

The breccias contain abundant but disconnected pillowlike nodules of basalt, and fragments derived from 

them, in a matrix far richer in glass and palagonite 

than that of subaerial Icelandic tuffs. Breadcrust
C40 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

bombs, scoria, airborne ash, and lapilli are lacking in 

the palagonitic complexes. Masses of pillow lavas, 

with primary dips to 30°, are abundant. Overlying 

many of these piles of palagonite breccia are irregular 

nodular flows, which in turn are overlain by normal 

subaerial basalt flows. Published descriptions of the 

various tuff, breccia, and nodular occurrences could 

largely be applied to the analogous complexes in the 

Hallett region, but the proportion of palagonitic breccias and tuffs low in the section is much greater in 

the Antarctic volcanic piles than in the Icelandic ones, 

and the Antarctic piles lack good pillow lavas.

The steep sides of the table mountains are regarded 

as constructional, not erosional, by most Icelandic 

geologists (but not by Einarsson, 1966), and as generally interpreted by them require accumulation 

against ice walls: the mountains were built by volcanism in cylindrical chambers that were melted in the 

ice from beneath by volcanic heat. The first eruptions 

must have occurred in vaults at the base of the ice, 

and the final subaerial lavas must have formed after 

the structures were built above the ice level or after 

the ice had receded. The nodular lavas just beneath 

the capping subaerial lavas presumably hardened at 

shallow depths beneath the lake surfaces. The many 

geologists studying the palagonite complexes agree 

that they were deposited wholly under water that was 

in contact with ice but disagree on details, such as 

which of the breccias were erupted under water and 

which were erupted explosively above the melt-water 

lakes from lava that was quenched by its rise through 

the saturated pile.

ORIGIN OF THE ANTARCTIC BRECCIAS

Like the Icelandic breccias, the breccias of the 

Hallett region formed in contact with water and were 

hydrated when hot. The palagonite tuffs were water 

laid. Fragmentation and hydration of lava produced 

palagonite breccias. Some of these were hot and mobile 

and moved as thick masses that contained molten or 

solid lava lenses which were deformed and fragmented 

by the motion of the whole. Concentrically structured 

spheroids of lava, now clasts in the breccias, crystallized from detached globs of magma in hot, moving 

breccias. Other breccias were less mobile and grew 

upward and outward primarily by the outflow of new 

material on their surfaces rather than by motion of 

the body as a whole. Lava within the hot breccias intruded them complexly as dikes, sills, and megapillows; small intrusions may have had little relation to 

vent areas, representing instead only migrations of 

magma within mobile breccias. The mobility of the 

breccia is further demonstrated by the abundant clastic

dikes of palagonite breccia. Many eruptive units display an upward succession from chaotic breccias to 

thinly interlayered lava and breccia, showing that 

fluidity of extrusions in such units increased during 

the eruptive episodes. Units hundreds of meters thick 

formed during single episodes of eruption. The cones 

of moderately dipping palagonite tuff demonstrate 

that some of the breccia units had steep sides at least 

several hundred meters high, down which the tuff 

cascaded.

The steep temporary sides of the breccia units recorded by the cones perhaps occur where extrusions 

were dammed against the ice walls of the melt-water 

vaults, the cones having formed after the ice wall 

melted back. Violent convective currents in the water 

around the hot breccias may have winnowed out the 

fine clasts and carried them to the sides of the masses 

to what became the apexes of the cones. Continuing 

growth of the breccias buried the cones. Breccias may 

also have been extruded upon ice and may have then 

been jumbled when the ice was melted.

Basalt magma, chilling from its liquidus to 0° C, 

could melt ice to about ten times its own volume 

(Goranson, 1942). Actual melting would be less, for 

much heat would be lost to the atmosphere through 

steam escaping to the surface and through evaporation 

of hot water after melting had produced a lake reaching the ice surface. Presumably the melting would 

tend to form an upward-widening conical chamber 

within the ice. The thinner the ice cap above the vent 

and the more voluminous the eruption, the greater the 

likelihood that melting would proceed to the surface 

and produce a lake rather than a melt-water vault at 

the base of the ice.

A melt-water vault, pressurized and partly sealed 

by the overlying ice, might contain very hot water 

with or without steam, or even supercritical water, in 

contact with the eruptive mass. Rapid loss of heat 

from magma should produce a violently convecting 

water mass varying greatly in temperature. (This 

situation is not to be compared with eruption into a 

lake or the ocean, for the water volume would be small 

proportional to the lava volume, and a large allowance must be made for melting inertia of the ice and 

loss of heat to the atmosphere.) On the other hand, 

insulation of the igneous mass by a thick chilled crust 

would retard the release of heat, and the vault or 

lake could then be filled with cool water.

An origin of the breccias by submarine eruptions is 

not indicated. Breccias of this type are not known 

elsewhere in submarine complexes; and compact pillow 

lavas are lacking here. Were the breccias submarine, 

they would have had to be erupted in water 2,000 m
HALLETT VOLCANIC PROVINCE 041

deep fully oceanic depths yet continental basement 

rocks lie beneath them; and all of the uplift to present 

altitudes would have to have occurred in late Quaternary time.

The contrast between the Antarctic breccias and the 

products of submarine eruptions is perhaps due in 

considerable part to the presence of very hot water in 

contact with the lavas. The breccias were saturated 

with water liquid, steam, or supercritical from the 

times of their initial fragmentation, which presumably 

was at a temperature near their solidus, throughout 

their cooling histories. The slower the cooling, the 

more thorough would have been the palagonitization 

of small clasts. Water fluidized the breccias and permitted them to flow. Chilled margins were produced 

on masses of lava mixed into cold breccias, but not 

where breccias were hot.

The altitudes of the breccias provide minimum 

thickness for the past ice sheet of the Ross Sea. The 

upper limit of exposed ice-contact breccias is at an 

altitude of about 1,500 m at the .southwest end of 

Hallett Peninsula (fig. 18), 1,500 m on Coulman Island, 1,700 m on the seaward side of Hallett Peninsula, 

1,800 m on the seaward side of central Adare Peninsula (fig. 21), and higher than 600 m on the outer 

coast of Daniell Peninsula. Ice grounded on the continental shelf of the Ross Sea, about 500 m below 

present sea level, reached to at least these altitudes 

above sea level. It was shown previously that even the 

Adare Peninsula limit is compatible with formation 

against an ice sheet grounded across the continental 

shelf.

There are few volcanic rocks which could be interpreted as subaerial I recognized none that are certainly subaerial below the capping veneers of the 

various volcanic piles. Throughout most of the period 

of volcanism in the region, then, the Antarctic ice 

sheet was much more extensive than it is at present, 

and grounded ice thickly filled the Ross Sea region.

LATE CENOZOIC GLACIATION OF ANTARCTICA

The late Miocene and Pliocene age determinations 

for basalts in subglacial breccias low in the Hallett 

and Coulman volcanic piles indicate that ice grounded 

on the continental shelf of the Ross Sea, far beyond 

present ice limits, existed throughout late Cenozoic 

time. This conclusion is in accord with much information obtained in the last few years from Antarctica 

and the Southern Ocean.

In the McMurdo Sound region of South Victoria 

Land, most of the glacial sculpturing of valleys now 

largely free of ice occurred before the eruption of

basalts 2.7-3.7 m.y. ago (Armstrong and others, 1968; 

Denton and others, 1970), and hence within Tertiary 

time. In Marie Byrd Land, ice-contact breccias of several early (the oldest date is given as 42±9 m.y.), 

middle, and late Cenozoic ages have been found by 

Le Masurier (1970), indicating at least intermittent 

glaciation beyond present ice levels during much of 

the Tertiary.

Antarctic and Arctic waters are now characterized 

by sinistrally coiled Globigerina, pachyderma (a 

planktonic foraminifer). This foram had major expansions toward the equator in the middle Pliocene 

and very late Miocene, indicating that the Greenland 

and Antarctic ice sheets were probably then much 

more extensive than they are now (Bandy, 1968). No 

period markedly warmer than the present is recorded 

in the sediments representing the last 5 m.y. in the 

Southern Ocean (Goodell and others, 1968).

The Antarctic Convergence is marked by its high 

biological productivity and correspondingly high rate 

of pelagic sedimentation. The thickest pelagic sediments of the Southern Ocean lie between 50° and 

55° S., considerably north of the present convergence, 

and indicate that during most of the past 10 m.y. or 

so the convergence has been well north of its present 

position (Ewing and others, 1969). This accords with 

the concept that Antarctica was ice covered well beyond present ice limits during most of late Miocene 

and Pliocene time.

Margolis and Kennett (1971) studied subantarctic 

deep-sea cores and identified early Eocene, late-middle 

Eocene, and Oligocene episodes of Antarctic glaciation 

on the basis of the presence of ice-rafted sand (recognized by electron microscopy) and of low-diversity 

foraminiferal faunas in the sediments. They found a 

general warming recorded through the early and middle Miocene by increasing species diversity and by 

lack of rafted sand. A sharp cooling is recorded in 

the late Miocene sediments, and continued cold since.

A worldwide drop in sea level during late Miocene 

time is suggested by many data from some relatively 

stable coastlines, and the drop presumably accompanied the onset of major glaciation in Antarctica 

(Alt, 1968; Kennett, 1967). Shorelines in the southeastern United States record a marked eustatic drop 

of sea level following late Miocene time, from a level 

of about 70 m above present sea level; Pliocene levels 

were at their highest about 30 m above present sea 

leA^el, and Quaternary ones fluctuated from 15 m above 

to far below the present level (Alt, 1968). The late 

Miocene withdrawal of water needed to cover Antarctica with an ice sheet would account quantitatively 

for the Miocene and Pliocene sea levels.
C42 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

The extensive and prolonged late Miocene and Pliocene glaciation of Antarctica renders untenable the 

speculation by Hollin (1962) and Grindley (1967) 

that Antarctic glaciation markedly more extensive 

than that of the present could occur only when sea 

level was lowered by widespread glaciation in the 

Northern Hemisphere. The Antarctic data give no 

support to the more general assumption by some 

geologists (for example, Pewe, 1966) that Antarctic 

glacial advances have been synchronous with the 

glaciations of middle northern latitudes.

Ice-contact breccias such as characterize the volcanic 

piles of the Hallett province are, as noted in the introduction, uncommon in the McMurdo volcanic province 

at the south end of the Boss Sea. I infer from this that 

the exposed McMurdo volcanic rocks are largely of 

Quaternary age and that they postdate the great late 

Miocene and Pliocene ice sheet of the Ross Sea.

EROSION

The offshore volcanic piles have constructional 

upper surfaces formed of upper Quaternary lavas and 

tuffs but largely covered by ice caps. These surfaces 

where exposed show evidence of only minor glacial 

erosion.

The sides of the volcanic piles by contrast are mostly 

erosional cliffs which fall sheer from the summit surfaces to sea level. The volcanic structures are formed 

mostly of poorly consolidated tuffs and breccias which 

are subject to rapid erosion. Marine and glacial erosion have both obviously contributed to the formation 

of the cliffs, although the proportion of each is uncertain. These cliffs are highest on the seaward (east) 

sides of the piles and reach a height of 2,000 m on the 

east face of central Adare Peninsula. The height of 

the cliffs is largely a measure of the amount of lateral 

erosion into the volcanic structures, although steep 

sides of primary "table mountains" may have contributed. Each pile, if complete, would be a symmetrical elongate dome with a maximum crestal altitude 

of about 2,000 m. Coulman Island and the northern 

two-thirds of Daniell Peninsula preserve this symmetry and have been cut back only moderately from 

the sides. Hallett and Adare Peninsulas by contrast 

have been eroded from the east to or beyond their 

crestlines: more than half of each volcanic pile has 

been removed by erosion.

Erosion by the Ross Sea ice sheet may have caused 

much of the erosion of the seaward sides of the peninsulas and of both sides of Coulman Island. The highest cliffs that are clearly attributable to glacial erosion, 

however, are those on the south side of Hallett Peninsula, where Tucker Glacier has cut cliffs as high as

1,200 m (fig. 16). The lower cliffs on the west sides 

of Daniell and Hallett Peninsulas must also have been 

cut largely by ice.

Marine erosion must have contributed to all the 

seaward cliffs and may have been the dominant factor 

in their formation. Antarctic storms are the most 

violent on earth and wave attack must be correspondingly severe during open-water periods. Strong currents flow northward along the west side of the Ross 

Sea and may serve to carry away and redistribute 

debris eroded from the volcanic piles. The cliffs 

bounding the islands and stacks of the Possession 

group (fig. 23) are obviously sea cliffs and reach altitudes of 200 m, limited only by the elevations of the 

island summits.

Calderas have been breached by erosion, chiefly 

glacial, on Adare Peninsula (fig. 205), Daniell Peninsula (figs. 10, 11J., 12), and Coulman Island (fig. 7). 

The floors of the southern Daniell calderas are near 

sea level, so the breaching of these calderas gives their 

sector of the peninsula a very irregular map configuration. The walls of the calderas stand as cliffs where 

not buried by ice and reach heights of 2,000 m.

VOLCANIC ROCKS OF THE MAINLAND

Small masses of upper Cenozoic volcanic rocks lie 

on the Paleozoic rocks of the mainland west of the 

large offshore volcanic piles (figs. 4, 14, 17; the size 

of some of the exposures is exaggerated in fig. 4 to 

permit their depiction). All exposures shown north 

of 73° S. and east of 166° E. were seen during the 

present work; three of the localities were sampled on 

the ground, but the others were only mapped from the 

air. Larger masses of volcanic rocks are present in the 

coastal region south of 73° S. These were not visited 

in this work, but published information on them is 

summarized briefly.

VOLCANIC ROCKS NORTH OF 73° S. LATITUDE

The small mainland exposures of volcanic rocks 

north of 73° S. and east of 166° E. are of basalts and 

subordinate trachyte, which have been much eroded 

by ice.

The small mass between Whitehall and Borchgrevink Glaciers, west of central Daniell Peninsula 

(fig. 14), consists of basaltic aa breccia, which fills a 

small saddle on a ridge in Paleozoic metasandstone. 

The source of this remnant has been removed by 

erosion.

A minor vent area for olivine basalt eruptions is 

exposed near upper Trafalgar Glacier (loc. 215, fig. 

4). A bench eroded in metasandstone is partly covered
HALLETT VOLCANIC PROVINCE C43

by the glaciated remnant of a red scoria cinder cone, 

from which flowed an aa breccia flow. The metasandstone ridge crest above the bench is capped by a flow 

remnant of massive basalt and by an agglomerate of 

spatter, cinders, and bombs; the agglomerate remnant 

dips northwestward across the ridge, and the proportion of spatter increases updip, demonstrating that the 

vent from which it came and which has been removed 

by erosion lay to the southeast.

Vent-filling basalt in Paleozoic granodiorite is exposed at the northwest edge of Moubray Bay (loc. 210, 

fig. 17). The vent is exposed in the eastern cliffs of the 

ridge from an altitude of 50 meters to the crest at 200 

meters, and it widens upward to a diameter of 150 

meters. Harrington, Wood, McKellar, and Lensen 

(1967, p. 60-61) described the basalt and palagonite 

tuff and breccia of this vent.

The other small mainland masses of volcanic rocks 

shown on the maps were seen only from the air. They 

consist mostly of dark basalts capping minor ridges 

or benches and lacking obvious relationship to the 

present topography.

MOUNT OVERLORD AND MOUNT MELBOURNE

Two high, young volcanoes Overlord and Melbourne stand above low volcanic piles west and 

southwest of Coulman Island (fig. 4). Mount Overlord 

(fig. 32 J.) has been described briefly by Gair (1964, 

1967) and by Nathan and Schulte (1968). They found 

varied highly alkaline rocks: trachybasalt, trachyandesite, phono] ite, syenite, and alkaline gabbro. The 

symmetrical cone of Mount Melbourne (fig. 32Z?) also 

has been visited by New Zealand geologists who collected trachyandesite in the summit area and found 

active fumaroles and alkaline basalt, trachyandesite, 

and trachyte in other parts of the volcano (Nathan 

and Schulte, 1967, 1968). Smith (1964a, b) described 

erratics of basalt and trachyte collected by Priestley 

from Campbell Glacier.

Mount Overlord and Mount Melbourne resemble the 

main young volcanoes of the McMurdo Sound region 

in rising high and steep sided above their surroundings. They contrast correspondingly with the low central volcanoes that stand on the long coastal volcanic 

piles of the Hallett province. Harrington, Wood, McKellar, and Lensen (1967) suggested that such differences are due to a greater volcanic maturity of the 

dominant-cone terranes and that high, steep volcanoes 

may ultimately be built on the Hallett piles.

PETROLOGY

The volcanic rocks of the Hallett province constitute 

a very sodic assemblage containing approximately 70

B

FIGURE 32. Aerial views eastward over stratovolcanoes toward Wood 

Bay. A, Mount Overlord. The caldera rim of this highly alkaline 

volcano has an altitude of about 3,400 m. Mount Murchison stands 

on the center skyline and Coulman Island on the left. Photograph 

by U.S. Navy for U.S. Geological Survey, TMA 710, F 31, no. 342, 

altitude 6,000 m, 31 October 1960. B, Mount Melbourne. Summit 

altitude is about 2,500 m. Photograph by U.S. Navy for U.S. Geological Survey, TMA 325, F 31, no. 48, altitude 5,000 m, 3 December 

1956.

percent of alkaline olivine basalt and subordinate 

olivine trachybasalt, 15 percent of trachyte, and no 

more than a few percent each of basanite, andesine 

basalt, latite, phonolite, and quartz trachyte. Included 

are some of the most sodic igneous rocks yet reported 

anywhere. The assemblage is strongly bimodal: only 

a small amount of rock is intermediate between basalt 

and trachyte.
C44 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

Of the 250 hand specimens collected of the volcanic 

rocks, about 65 were selected for petrographic study, 

and 34 of those were used for whole-rock chemical 

analysis. A little X-ray work was done also. This 

reconnaissance study permits characterization of the 

broad features of the petrologic province.

ROCK CLASSIFICATION

Alkaline volcanic rocks vary greatly in mineralogic 

and chemical compositions. The following rock-name 

classification, used in this report, is based primarily 

on mineralogy, but available chemical analyses are 

integrated particularly for their information regarding the relative amounts of occult alkali feldspars and 

feldspathoids. Numbers refer to those reported in the 

tables of chemical analyses (tables 2, 3).

Felsic rocks

Trachyte leucocratic rock composed largely of 

alkali feldspar, \vhich may be sodic oligoclase, albite, 

aiiorthoclase, or sanidine, alone or in combination. 

(Analyses 8, 12, 23.)

Quartz trachyte trachyte containing quartz. 

(Analyses 13, 14, 19.)

Phonolite leucocratic rock composed mostly of 

alkali feldspar and feldspathoids. (Analyses 6, 7.)

Hydrated trachyte glass. (Analysis 9.)

Intermediate rocks

Latite contains moderate to large amounts of both 

alkali feldspar and andesine or calcic oligoclase and a 

small or moderate amount of mafic minerals; may 

contain a minor amount of feldspathoids. (Analyses 

22, 30.)

Mafic rocks

Basalt contains abundant plagioclase more calcic 

than andesine, and clinopyroxene. (No analyzed 

specimens.)

Andesine basalt mafic rock containing abundant 

clinopyroxene and little alkali feldspar, and in which 

the plagioclase is andesine rather than a more calcic 

variety. (No analyzed specimens.)

Trachybasalt contains plagioclase more calcic 

than andesine, abundant clinopyroxene, and a moderate amount of alkali feldspar. (Analyses 1-5, 11.)

Any of the above mafic rock types can contain small 

amounts of olivine, feldspathoids, or alkali feldspars. 

All carry substantial quantities of opaque minerals.

Olivine basalt contains abundant clinopyroxene 

and plagioclase more calcic than andesine, and more 

than 5 percent of olivine. Most is alkaline. (Analyses 

10, 15-18, 20, 21, 24-28, 32-34.)

Palagonite hydrated basalt glass. (Analysis 29.)

Ultramafic rocks

Basanite pyroxene-rich rock, containing olivine, 

minor feldspathoids, and little or no plagioclase. 

(Analysis 31.)

DISTRIBUTION OF ROCK TYPES

Field designations of rock type generally w^ere attempted only as to "trachyte" and "basalt," which 

correspond approximately to the "felsic" and "mafic" 

groups of rock types. Many of the trachytes are lightgray rocks, with or without an olive or yellowish 

cast; they display a bright sheen reflected from floworiented feldspars and can be identified at a glance. 

Many of the basalts are dark gray and contain conspicuous phenocrysts of pyroxene and olivine; hence 

they also are easily recognized. Between these twTo 

populations of readily distinguished rocks is a large 

family of medium-gray rocks, which include both 

mafic and felsic types and which where aphanitic and 

nonporphyritic were, in many instances, incorrectly 

designated in the field. The light-colored rocks w^ere 

purposely collected in more than their true proportion 

to the dark-colored ones. These factors and the small 

number of samples studied petrographically preclude 

the making of quantitatively accurate statements regarding frequency distribution of the rocks.

The occurrences of the trachytes and the other felsic 

rocks are in general the same as those of the mafic 

rocks. Trachyte forms hydrated breccias and tufi's, 

nodular lavas, megapillows, dikes, and plugs, just as 

does basalt in the breccia sections. The large calderas 

however may be produced only by trachytic eruptions: 

the rim of Coulman caldera is formed exclusively of 

trachyte where sampled, and in the rim of the similarly large caldera of southern Adare Peninsula 

trachyte and basalt occur together. Abundant trachyte 

was found both low and high in the Hallett pile, and 

a minor amount of trachyte wTas found low in each of 

the other piles.

The proportion of mafic to felsic rocks may be 

higher in the small mainland accumulations than in 

the large ofi'shore volcanoes.

PETROGRAPHY

The dominant rock types, alkaline olivine basalt and 

olivine trachybasalt, vary greatly in thin-section appearance. Many samples are holocrystalline, but even 

most of these are exceedingly fine grained, are clouded 

by opaque dust or tiny granules, and contain much 

material that cannot be fully identified by petrographic methods. Interstitial alkali minerals, glass and
HALLETT VOLCANIC PROVINCE C45

hydrated glass, and brownish secondary materials vary 

greatly in abundance. Many specimens are mostly 

vitric, the glass being either fresh or hydrated.

Olivine is present in most specimens of basalt and 

trachybasalt, but in these occurs mainly in amounts of 

only a trace to 5 percent; it was not seen to constitute 

much more than 10 percent of a specimen. Olivine is 

greenish yellow to nearly colorless where fresh and 

occurs entirely as small phenocrysts in some specimens 

and as phenocrysts and groundmass granules in others. 

The phenocrysts are variously euhedral, fragmental, 

and resorbed, only one of these types being abundant 

in any one specimen. The phenocrysts are altered in 

various degrees to iddingsite(?) in some specimens, 

and the groundmass granules in some samples are 

completely altered.

The pyroxene in the basaltic rocks is exclusively 

monoclinic and pale colored. Most of the phenocrysts 

are yellowish gray or dusky yellow in thin section. 

Phenocrysts in some specimens have narrow yellowishbrown rims. Groundmass granules and microprisms 

are faintly green or pale yellowish brown. Pleochroism 

is weak, and extinction angles mostly moderate. Some 

of the basalts and trachybasalts contain abundant 

phenocrysts of augite that is black and of almost 

vitreous appearance in hand specimen.

Plagioclase in the basaltic rocks occurs primarily as 

groundmass laths but also forms sparse phenocrystic 

tablets or fragments in many specimens. The composition is typically labradorite, but andesine is common 

and some bytownite was found. Interstitial anhedra 

of alkali ieldspar are present in amounts up to about 

15 percent in many specimens; the grains are too small 

to be satisfactorily identified optically, but X-ray examination of specimens by George M. Fairer (written 

commun., 1967) revealed the common presence of 

high-temperature anorthoclase. Anhedral nepheline 

was recognized in only a few sections. Analcite is 

common both as a filling or lining of vesicles and as an 

anhedral groundmass mineral.

Much of the basalt and trachybasalt occurs as palagonite tuff and breccia. The tuff and breccia consist 

of clasts of all sizes, from less than a millimeter to 

many meters, of widely varied basalts, in porous 

frameworks whose interstices are partly filled by clays, 

calcite, and analcite and other zeolites. The smaller 

clasts typically have groundmasses of yellowish-orange 

nearly isotropic hydrated glass palagonite. Most of 

the larger clasts are much less altered, even though 

they too contain considerable clay, carbonate, and 

zeolite. Most of the clasts display rapid chilling in 

their fabrics.

Most of the trachytes are porphyritic with wellshaped or resorbed phenocrysts of oligoclase (uncommonly andesine) or anorthoclase, or both. Groundmasses are mostly dominated by flow-alined laths of 

alkali feldspar that is variously oligoclase, albite, 

sanidine, and anorthoclase. Interstitial material consists of anhedra of alkali feldspar, analcite, and 

nepheline(?), glass, and unidentified secondary minerals. The dominant mafic silicate is clinopyroxene, 

generally greenish, limited to the groundmass, and 

variously acicular, granular, and anhedral. Some 

specimens contain long prisms of brown hornblende, 

which are more or less replaced by opaque granules. 

A little olivine, or reddish iddingsite(?) after it, is 

present in some of the trachytes, and a little brown 

biotite occurs in others. Opaque dust and granules are 

generally abundant, and they render the groundmasses 

of some trachytes nearly opaque, as seen in thin section.

The trachytes also form hydrated tuffs which occur 

in the same manner as the basaltic palagonites. Clasts 

of trachyte varying widely in texture and mineralogy 

are much altered to clay, analcite, and other secondary 

minerals.

Latites are common but subordinate in amount to 

trachytes. The latites contain phenocrysts of andesine 

and either augite or brown hornblende, or both. 

Groundmasses display laths of andesine or oligoclase, 

abundant microprisms of clinopyroxene and granules 

of opaque minerals, generally some olivine or iddingsite, and much alkali feldspar, glass, analcite, and secondary minerals.

The three specimens of quartz trachyte that were 

examined all contain phenocrysts of anorthoclase, 

which shows at most poorly developed grid twinning. 

Groundmasses are dominated by flow-alined laths of 

alkali feldspar, mostly sanidine in one specimen, but 

mostly albite in two others which contain also abundant anhedral interstitial anorthoclase. Quartz occurs 

as veinlets, tiny pods, and interstitial anhedra in two 

of the specimens, and the chemical analysis of the 

third indicates the occult presence of quartz in glass. 

One of the quartz trachytes contains sparse microphenocrysts of green clinopyroxene, one contains a 

fibrous secondary amphibole, and the third has a 

barkevikitic.(?) amphibole. Opaque minerals, as dust, 

granules, and interstitial or replacement anhedra, are 

abundant in all three specimens.

Phonolite was recognized in only one occurrence 

an intrusive megapillow on the east side of Hallett 

Peninsula but it presumably is present elsewhere. 

The holocrystalline specimen that was examined consists of about one-third nepheline, one-third sanidine, 

and one-third total clinopyroxene, opaque minerals, 

oligoclase, hornblende, natrolite, and analcite.
C46 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

Only one specimen that was identified certainly as 

basanite was studied in thin section. This is a pyroxenerich olivine-bearing ultramafic volcanic rock which 

contains no visible feldspar or feldspathoid, although 

its chemical analysis indicates that a little calcic 

plagioclase and considerable feldspathoid are occult in 

the brown glass that forms about a quarter of the 

specimen.

A single specimen of a possibly ultramafic volcanic 

rock type was examined in thin section but was not 

analyzed chemically. This rock contains about 10 percent of tiny grains of augite, 25 percent of yellowishbrown hornblende, and 5 percent of fresh olivine, in 

glassy matrix clouded by opaque material. No feldspar is visible.

ULTRAMAFIC INCLUSIONS

The only ultramafic inclusions found are sparse 

granule-sized aggregrates, presumably cumulates, of 

olivine and augite in some of the basaltic rocks.

HIGH-PRESSURE MEGACRYSTS

The rocks in which the small ultramafic aggregates 

occur typically also contain abundant large separate 

crystals of minerals which are more likely to be products of deep-crustal or upper-mantle crystallization 

than of shallow crystallization. Large to at least 1 

cm equant crystals of augite, black and nearly vitreous as seen in hand specimen and lacking conspicuous cleavage, typically occur in these rocks. So do 

corroded or reaction-rimmed crystals of olivine, 

smaller than the augites but larger than is typical in 

most of the other basaltic rocks. Sparse, large to as 

much as 2 cm hornblende prisms are present. A single 6-mm octahedron of dark-gray spinel was noted. 

These minerals resemble the high-pressure megacrysts 

described by Binns (1969) from compositionally similar basalts and basanites in Australia. Binns deduced 

that the pressure at the site of crystallization of the 

megacrysts was between 10 and 18 kb, indicating a 

depth between 35 and 65 km. The large corroded crystals of plagioclase and anorthoclase in many basaltic 

and trachytic rocks of the Hallett province may also 

be products of crystallization at depth.

DESCRIPTIONS OF ANALYZED SPECIMENS

The 34 rock specimens for which chemical analyses 

are reported in tables 2 and 3 are described briefly in 

this section. Two numbers are given for each specimen: 

the first is the column number of the sample in the 

tables, and the second, in parentheses, is the field number. The sample localities are indicated on the maps

(figs. 4, 6, 14, IT) by the field numbers without the 

suffixed letters (which distinguish types at each 

locality).

Hallett Peninsula 

Nos. 1-14 (table 2)

1 (213A). Nepheline-andesine trachybasalt. Dense mediumdark-gray rock, studded by small black crystals of hornblende 

and augite. Contains about 5 percent of seriate phenocrysts of 

olivine, pleochroic to dusky yellow; 1 percent of phenocrysts 

of labradorite with narrow rims of andesine; and less than 

1 percent of phenocrysts of brown hornblende rimmed by 

opaque granules. Groundmass consists of subequal amounts 

of tiny (0.02 mm long) prisms of greenish clinopyroxene and 

of alined laths (0.05-0.6 mm long) of andesine (^Anss), 

with abundant granules (0.004-0.5 mm) of opaque minerals 

and abundant poikilitic anhedra of anorthoclase and nepheline. 

Sparse nepheline crystals are euhedral. Apatite and carbonate 

occur in minor amounts. Subaerial flow capping ridge west of 

Arneb Glacier at altitude 450 m (fig. 14).

2 (214B). Nepheline trachybasalt. Dense medium-dark-gray 

rock studded by small black phenocrysts. Seriate augite 

euhedra to 3 mm long are faintly pleochroic in pale olive 

and form 3 percent of the rock; phenocrysts of brown hornblende rimmed by opaque granules form 1 percent. Plagioclase 

(^Anso) laths, most shorter than 0.2 mm, form 10 percent of 

the groundmass, which consists largely of dark and extremely 

fine grained holocrystalline material containing very abundant 

0.002-mm granules of opaque minerals, granules and tiny 

prisms of green clinopyroxene, and very poikilitic finely granular nepheline and alkali feldspar. This specimen is almost identical chemically to number 1 and may be from the same 

lava flow, but it is very different petrographically, for it contains little plagioclase, and that markedly more calcic than 

in the other specimen, so the granular feldspars must differ 

markedly. Subaerial flow capping ridge west of Arneb Glacier 

at altitude of about 600 m (fig. 14).

3 (212C). Olivine-andesine trachybasalt. Dense mediumlight-gray rock. Holocrystalline and nonporphyritic. Contains 

about 40 percent andesine ('^ A.nss) in laths 0.1-0.5 mm long, 

in part enclosed in ophitic plates of titaniferous (?) paleyellowish-brown augite (about 20 percent of the rock), and 

in part separated by anhedra of sodic anorthoclase (refractive 

index «* balsam; confirmed by X-ray methods; about 20 percent of rock). Small grains of slightly altered yellowish 

olivine form about 5 percent of the rock, and opaque granules 

about 8 percent. Nepheline appears in the norm (4 percent) 

but was not recognized petrographically. This rock is similar 

in bulk composition to samples 1 and 2 and may belong to 

the same flow, but it is quite distinct petrographically from 

either of the others. Subaerial flow capping ridge west of 

Arneb Glacier at an altitude of about 300 m (fig. 14).

4 (212A). Analcite-olivine trachybasalt. Medium-gray rock 

that contains sparse small vesicles. Nonporphyritic, holocrystalline, fine grained. About half the rock consists of laths 0.1-0.5 

mm long of plagioclase (' A.n50 ), and about 15 percent consists of yellowish-gray to greenish-yellow clinopyroxene in 

needles and short prisms shorter than 0.03 mm. Variably 

iddingsitized olivine crystals smaller than 0.1 mm form 5 

percent of the rock; analcite constitutes a similar amount, 

occurring both as a groundmass mineral and as vesicle linings. 

Anorthoclase anhedra constitute about 15 percent of the rock,
HALLETT VOLCANIC PROVINCE C47

and opaque granules about 7 percent. Analcite, anorthoclase, 

and phillipsite were identified by G. M. Fairer by X-ray 

methods; phillipsite was not recognized optically. Pillow-clast 

in palagonite breccia, at altitude of about 275 m on ridge west 

of Arneb Glacier (fig. 14).

5 (211B-2). Olivine-andesine trachybasalt. Dense mediumdark-gray rock speckled by lighter spots 2-3 mm in diameter. 

Holocrystalline, fine grained. About 50 percent of the rock 

consists of plagioclase one-third of it in seriate tabular phenocrysts to 2 mm long of labradorite (' Anao), the rest in 

0.1-mm laths of andesine (< An40 ). Olivine, partly altered to 

iddingsite, constitutes 5 percent of the rock and occurs mostly 

as groundmass granules but partly as microphenocrysts. About 

15 percent of the rock consists of 0.005- to 0.01-mm granules 

and microprisms of pale-olive clinopyroxene, a like amount 

consists of poikilitic 0.01-mm anhedra of anorthoclase, and 10 

percent consists of opaque granules and microphenocrysts. 

Apatite, calcite, and analcite are present in amounts of a 

percent or so each. Pillow (?) -lava complex in the palagonite 

breccia section, altitude 180 m on the ridge west of Arneb 

Glacier (fig. 14).

6 (247A). Augite-sanidine-nepheline phonolite. Massive, 

medium-light-gray holocrystalline rock. The texture is chaotic, 

with patchy distribution of masses of varying texture and 

mineralogy, a dominance of anhedral and poikilitic shapes, 

and an abundance of replacement relationships. Phenocrysts: 

oligoclase, about 3 percent, in tablets to 4 mm long, variably 

replaced by granular nepheline and zeolites; augite, about 5 

percent, pleochroic in olive green, with or without duskyyellow cores; and pseudormophs, about 3 percent, of finely 

granular augite and opaque minerals after brown hornblende, 

which remains as ragged cores in some pseudomorphs. The 

groundmass consists mostly of ragged-edged tablets of sanidine, typically about 1 mm long, composing about 35 percent 

of the rock, and anhedra of nepheline, also about 35 percent, 

which partly are interspersed with sanidine and partly occur 

in purer masses of ragged anhedra. Natrolite and analcite 

each composes about 5 percent of the rock, and occur in part 

in masses of these two minerals alone or with calcite, and 

in part as groundmass anhedra throughout the rock. Small 

ragged anhedra of augite constitute about 5 percent of the 

rock and are dispersed throughout it, as are small granules 

of opaque minerals. Interior of an intrusive megapillow, east 

side of Hallett Peninsula (fig. 14).

7 (247B). Phonolite. Light-olive-gray rock, seamed by a 

fine network of white to olive veinlets of analcite or calcite, 

or both. The rock consists largely of a fine-grained (' '0.01 

mm) hash of high-birefringence clay, clinopyroxene granules, 

zeolites, and unidentified felsic minerals. Scattered through 

this are several percent each of microphenocrystic laths of 

sanidine and euhedra of nepheline and their argillitic pseudomorphs, and a few percent of tiny needles of hornblende 

pseudomorphed by finely granular clinopyroxene and opaque 

minerals. Margin of intrusive megapillow (same mass as no. 

6), east side of Hallett Peninsula (fig. 14).

8 (236B). Olivine - clinopyroxene - anorthoclase - oligoclase 

trachyte. Dense aphanitic holocrystalline medium-gray rock. 

Sparse phenocrysts of oligoclase as thin tablets, anorthoclase 

as stubby, resorbed, poikilitic crystals, variably altered olivine, 

and green aegerine-augite (?), which is pleochroic in pale 

olive and has a large +2V. Groundmass consists of laths of

oligoclase, granules of green clinopyroxene, iddingsite, and 

opaque minerals, and very poikilitic small anhedra of anorthoclase and possibly feldspathoids. Large lava pod in palagonite 

breccia, altitude 280 m, west side of Hallett Peninsula (fig. 

14).

9 (249E). Hydrated trachyte tuff. Earthy yellowish-gray 

rock. Consists of poorly defined clasts, mostly a few millimeters 

in diameter, of texturally varied trachytes, greatly altered to 

clay, analcite, and other minerals. Most clasts contain tiny 

laths of sanidine, small equants of anorthoclase, and opaque 

granules. The thin section contains one cluster of small 

clinopyroxene phenocrysts pleochroic in green. Matrix for 

breccia, east side of Hallett Peninsula near Cape Wheatstone 

(fig. 14).

10 (274-1). Olivine basalt scoria. Mottled grayish-red and 

reddish-gray finely scoriaceous rock. Seriate phenocrysts of 

pale-olive augite, and fewer of olivine, are set in a groundmass 

of laths of labradorite, granules of clinopyroxene, fewer granules of iddingsite, minute crystals of unidentified alkali minerals, and hematite-clouded glass. Cinder cone, altitude 1,700 

m, east of crest of Hallett Peninsula (fig. 14).

11 (249D). Porphyritic trachybasalt. A rock of striking 

appearance: abundant black equant euhedra of augite to 1.5 

cm in diameter are set in a grayish-red groundmass. The 

augite phenocrysts are pleochroic in pale olive and have narrow rims pleochoric in pale yellowish brown. There are sparser 

phenocrysts of yellowish pseudomorphs after olivine and of 

calcic labradorite. The groundmass is holocrystalline and consists of laths of sodic labradorite, anhedral anorthoclase, subophitic augite, pleochroic in pale yellowish brown, and granules of iddingsite and of opaque minerals. Center of steep 

dike about 5 m thick, intrusive into trachyte breccia; east 

side of Hallett Peninsula, near Cape Wheatstone (fig. 14).

12 (246C). Trachyte. Medium-gray microvesicular rock 

containing sparse euhedral phenocrysts of andesine. The dominant mineral is oligoclase, which forms seriate laths 0.02-0.5 

mm long, the larger ones showing marked flow parallelism. 

The groundmass also contains tiny anhedra of anorthoclase(?), 

minute needles of greenish clinopyroxene, abundant opaque 

granules, irregular volumes in which hematite is concentrated, 

masses of highly birefringent light-brown material, and a 

little glass. Interior of dike, half a meter thick, cutting 

trachyte plug, east side of Hallett Peninsula (fig. 14).

13 (246A). Quartz trachyte. Dense yellowish-gray rock peppered with dark minerals. Fractures parallel to strong flow 

structure display bright sheen. Euhedral phenocrysts of 

anorthoclase make up a few percent of the rock. The groundmass is formed mostly (about 80 percent) of densely packed 

well-oriented laths of sanidine, typically about 0.3 mm long 

and having smooth side pinacoids and less regular other 

faces. Other minerals are ragged and interstitial and are 

irregularly distributed. Extremely irregular quartz constitutes 

about 5 percent of the rock. There are two amphiboles a 

dusky-yellow nonpleochoric low-birefringence fibrous one that 

contains rare cores of altered clinopyroxene, and an extremely 

pleochroic (dark-green, yellowish-brown, nearly opaque bluishgreen) high-birefringence amphibole which in part occurs as 

separate anhedra and in part occurs as tips and margins of 

anhedra of the fibrous amphibole. The dark amphibole may 

be a barkevikitic hornblende; the two amphiboles together 

make up about 5 percent of the rock. A few percent of the
TABLE 2. Chemical analyses and, calculated, components of volcanic rocks of Hallett Peninsula

[Specimens described in text; sample localities shown on fig. 14. Samples 1, 2, 3, 4, 5, 10, 11, 13, and 14 analyzed in U.S. Geol. Survey labo

oxides by Ellen S. Daniels by gravimetric methods, and 6-step semiquantitative sp eetrographic analyses by A. L. Sutton, Jr. Samples 6, 7, 

Geol. Survey laboratories, Washington, D.C., 1965; major oxides by X-ray fluorescence and colorimetric methods by P. L. D. Elmore, Samue

6-step semiquantitative speetrographie analyses by J. L. Harris, n.d., not determined. Looked for but not detected : Ag, As, Au, B, Bi, Cd, Eu, 

Re, Sb, Sm, Sn, Ta, Te, Th, Tl, V, and W]

Trachybasalt flows

Field No.

1

. _ 213A

2 

214B

3 

212C

Trachybasalt

nodular lavas

4 5 

212A 211B-2

Megapillows 1

Phonolite Trachyte

Interior

6 

247A

Margin

7 8 

247B 236B

lydrated Olivine 

brachyte basalt 

tuff scoria

9 10 

249E 274-1

Di

Trachybasalt

11 

249D

Major oxides as analyzed, weight percent

SiO2

AbOs ___ -

Iron : 

FeaOs ____ 

FeO

MgO -

PnO

Na2O

K2O

H2O+

H2O

TiO2

PsOs ___ _____________

MnO

CO2

Cl

F

Less O

Total

45.30

. _ 17.77

4.30

. _ 6.66

_ _ (10.5)

4.09

9.07

5.26

1.96

.40

.34

. _ 2.49

. _ 1.16

.24

.78

.16

_ _ .13

. _ 100.11

. _ .09

100.02

45.86 

17.99

4.06 

7.13 

(10.8) 

4.07 

9.17

5.37

1.84 

.33 

.10 

2.56

1.14 

.24 

.02 

.13 

.14

100.15 

.09

100.06

46.25 

17.45

6.04 

6.03 

(11.5) 

4.33

8.80

4.41 

1.81 

.17 

.15

2.89

1.07 

.23 

.31 

.09 

.11

100.14 

.07

100.07

45.64 48.51 

17.28 17.71

8.3 4.85 

3.69 6.25 

(11.1) (10.6) 

4.20 3.45

8.7 8.00

4.0 5.07 

1.80 1.80 

1.14 .27 

.73 .10 

2.78 2.47

1.08 1.16 

.22 .24 

.22 .16 

.08 .03 

.10 .09

100.02 100.16 

.06 .05

99.96 100.11

51.7 

20.6

2.4 

2.3 

(4.5) 

1.0 

3.5

10.0 

3.1 

2.9 

.17

.72

.21 

.30 

.49 

n.d. 

n.d.

99

53.0 56.1 

20.9 17.7

3.0 5.3

.80 2.8 

(3.5) (7.6) 

.2 1.2 

1.9 3.4

10.2 7.0 

3.9 3.4 

3.9 .70 

.28 .40 

.24 .94

.02 .38 

.31 .35 

.80 .15 

n.d. n.d. 

n.d. n.d.

99 100

58.2 45.97 

12.5 16.25

3.3 9.38 

.14 1.73 

(3.1) (10.2) 

.7 6.88 

2.3 9.92

5.1 4.19 

3.0 1.69

8.4 .18 

5.2 .08 

.24 2.76

.02 .64 

.13 .20 

.69 .07 

n.d. .12 

n.d. .11

100.17

.08

100 100.09

42.85 

14.05

10.45 

2.25 

(11.7) 

6.90 

10.56

2.55 

1.33 

1.29 

1.54 

3.00

.47 

.18 

2.35 

.10 

.09

99.96 

.06

99.90

Minor elements, weight percent

Ba

Be

Ce

Co

Or

Cu

On

La _ .

Mo

Nb

Nd

Ni

Pb

Sc

Sr

V

Y

Yb

Zr

. _ 0.1

. _ 0

.02

. _ _ .002

.002

. _ .003

. _ .003

.01

0

.01

.015

. _ .002

- - _ 0

. _ .001

.2

. _ .02

. _ .002

.0003

.03

0.1 

0 

0 

.002 

.001

.005 

.003 

.01 

0 

.01

.015 

.002 

0 

.001 

.15

.02 

.002 

.0003 

.03

0.05 

0 

0 

.003 

.002

.003 

.003 

.01 

0 

.007

.015 

.002 

0 

.0015 

.15

.02 

.002 

.0003 

.02

0.07 0.07 

0 0 

0 .015 

.003 .002 

.002 .0007

.003 .002 

.003 .003 

.01 .01 

0 0 

.007 .01

.015 .02 

.002 .001 

0 0 

.0015 .001 

.15 .15

.03 .015 

.003 .002 

.0003 .0003 

.03 .03

0.1 

.0005 

.05 

0 

.0003

.0007 

.002 

.03 

.001 

.007

.02 

0 

0 

0 

.15

0 

.003 

.0003 

.02

0.1 0.1 

.0005 .0003 

.07 .05 

0 0 

0 .0003

.00015 .002 

.002 .002 

.05 .03 

.0007 .001 

.01 .01

.02 .02 

.02 0 

.0005 .0015 

0 0 

.1 .1

0 0 

.003 .003 

.0003 .0003 

.03 .1

0.03 0.07 

.0003 0 

.03 0 

0 .005 

0 .07

.00015 .007 

.0015 .003 

.015 .007 

0 .001 

.005 .01

0 .007 

.005 .015 

.0003 0 

0 .001 

.01 .15

0 .03 

.003 .002 

.0003 .0003 

.07 .03

0.03 

0 

0 

.005 

.02

.01 

.003 

.003 

0 

.005

0 

.01 

0 

.002 

.1

.05 

.002 

.0002 

.015

Major oxides, recalculated to 100 percent for components listed, weight percent

SiO2

AkOs

Fe2Os

FeO

MeO

46.0

18.0

. _ _ 4.4

. _ 6.8

4.2

46.0 

18.0 

4.1 

7.2 

4.1

46.5 

17.5 

6.1 

6.1 

4.4

46.6 48.7 

17.7 17.8 

8.5 4.9 

3.8 6.3 

4.3 3.5

54.0 

21.5 

2.5 

2.4 

1.0

56.1 56.9 

22.1 18.0 

3.2 5.4 

.9 2.8 

.21 1.2

68.0 46.0 

14.6 16.3 

3.9 9.4 

.16 1.7 

.8 6.9

45.2 

14.8 

11.0 

2.4 

7.3
CaO _ _ 9.2

NasO 5.3 K2O 2.0

TiO2 2.5 P2Os 1.2

MnO .24

9.2

5.4

1.9

2.6

1.1

.24

8.8

4.4

1.8

2.9

1.1

.23

8.9

4.1

1.8

2.8

1.1

.22

8.0

5.1

1.8

2.5

1.2

.24

3.7

10.4

3.2

.8

.22

.31

2.0

10.8

4.1

.25

.02

.33

3.5

7.1

3.5

1.0

.39

.36

2.7

6.0

3.5

.28

.02

.15

9.9

4.2

1.7

2.8

.6

.20

11.1

2.7

1.4

3.2

.5

.19

Normative composition

Salic :

Q (SiOs) 0

Or (K2O- AbOs'6SiO2 ) ___ 11.8

Ab (NasO- AbO3-6SiO2 ) __ 21.3

An (CaO- AbOs 2SiO2 ) ___ 20.0

Ne (Na2O« AbOs 2SiO2 ) __ 12.2

HI (NaCl) .27

Femic :

Ac (NasO'Fe2O3.4SiO2 ) __ 0

Wo (CaO-SiO2 ) 7.3

En (MgO SiOa) 4.6

Fs (FeO SiO2 ) 2.2

Fo (2MgO SiO2 ) 4.1

Fa (2FeO SiO2 ) 2.2

Mt (FeO Fe2Os) 6.3

Hm (FeaOs) 0

11 (FeO TiO2 ) 4.8

Tn (CaO TiO2 SiO2 ) 0

Pf (CaO«TiO2 ) 0

Ap [3(CaO-P2O5 ) »CaF2 ] __ 2.8

Fr (CaF2 ) .16

S Salic 65.6

g 

Femic 34.4

ifferentiation index :

(Q + Or + Ab + Ne) ___ 45.3

0

10.9

21.8

20.1

12.3

.22

0

7.3

4.3

2.6

4.1

2.7

5.9 0

4.9 00

2.7

.18

65.4

34.6

45.1

0

10.8

28.8

23.0

4.4

.15

0

5.6

4.3

.7

4.6

.8

8.8 0

5.5 00

2.6

.13

67.0

33.0

43.9

0

10.9

30.7

24.5

2.0

.14

0

5.0

4.3 0

4.5 0

4.7

5.3

5.4 00

2.6

.11

68.2

31.8

43.5

0

10.7

34.8

20.5

4.3

.05

0

4.8

3.1

1.4

3.9

1.9

7.0 0

4.7 00

2.8

.08

70.3

29.7

49.8

0

19.1

32.6

2.3

30.2 00

6.0

2.6

1.7 00

3.6 0

1.4 00

.5

0

84.1

15.9

81.9

0

24.4

36.7 0

29.3 00

4.1

.5

000

3.1 0

.5

00

.05

0

90.4

9.6

90.4

0

20.4

51.5

7.0

4.7 00

3.2

2.8 0

.19

0

7.6

.17

1.8 00

.9

0

83.4

16.6

76.5

15.3

20.7

50.4

2.8 000

4.4

2.0 000

.21

3.7

.5

00

.06

0

89.1

10.9

86.4

0

10.0

22.9

21.1

6.3

.20

0

8.9

7.7 0

6.6 00

9.4

4.1 0

1.0

1.5

.17

60.5

39.5

39.3

0

8.3

22.0

24.7 0

.17

0

10.8

9.6 0

6.0 00

11.0

5.4

.8

0

1.2

.15

55.1

44.9

30.3
C50 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

TABLE 3. Chemical analyses and calculated components of volcanic

[Specimens described in text; sample localities shown on figures 4, 6, 14, and 17. Samples 15, 16, 20, 22-28, and 31-34 analyzed in U.S. 

analyses by A. L. Sutton, Jr. Samples 17-19, 21, 29, and 30 analyzed in U.S. Geol. Survey laboratories, Washington, D.C., 1965: 

tative spectrographic analyses by J. L. Harris, n.d., not determined. Looked for but not detected: Ag, As, Au, B, Bi, Cd, Eu, Ge,

Mainland Coulman Island

	Olivine 

	basalt 

	plug

Sample No. _ ___ ___ 15

Field No. ____________ 210B

SlOa ________________ 44.89

AhOs _______________ 13.20 

Iron:

FteOs _____________ 2.40

FeO ______________ 8.26

(Total as FeO) ______ (10.4)

MgO _______________ 12.86

CaO _______________ 9.67

Na2O _______________ 3.11

K2O ________________ 1.15

H2O+ .79

HaO- _________________ .25

TiOa ________________ 2.31

PsOs ________________ .54

MnO ________________ .19

COa _________________ .38

Cl __________________ .04

F __________________ .07

Sum ___________ 100.11

Less O _________ .04

Total __________ 100.07

Ba ________________ ^05

Be _________________ 0

Ce _________________ 0

Co _________________ .005

Cr ___________ ___ .07

Cu ________________ .015

Ga ________________ .002

La ________________ .007

Mo _________________ 0

Nb ________________ .005

Nd _________________ 0

Ni __________________ .05

Pb _________________ 0

Sc ____ ____________ .002

Sn ________________ 0

Sr _________________ .1

V _________________ .05

T _______________ .002

Yb ___ .0002

Zr _ _______________ .015

SiOa ________________ 4575

AhOs _______________ 13.4

Fe2Os _______________ 2.4

FeO __________ 8.4

MgO ________________ 13.0

CaO ________________ 9.8

Na2O ________________ 3.2

K20 _________________ 1.2

TiO2 _________________ 2.3

P2Os ________________ .6

MnO ________________ .19

SaUcl

8

(SiO2 ) _________ 0

r (K2O« Al2Os«6SiO2 ) _ 6.9

Ab (Na2O« A12O8 «6S1O2 ) 14.2

An (CaO« AhOs 2SiO2 ) _ 19.1

Lc (K2O AhOa 4SiO2 ) _ 0

Ne (Na2O Al2Os 2SiO2 ) 6.6

HI (NaCl) __________ .07

Femic:

Ac (Na2O FezOa 4SiOa) 0

Wo (CaO SiO2 ) ______ 10.7

En (MgO«SiO2 )______ 7.5

Fs (FeO SiOa) ______ 2.3

Fo (2MgO«SiO2 ) ____ 17.5

Fa (2FeO SiO2 ) _____ 5.8

Mt (FeO«Fe2O8 ) _____ 3.5

Hm (FteOa) _________ 0

II (FeO-TiO2 ) ______ 4.4

Tn (CaO«TiO2 «SiO2 ) __ 0

Pf (CaO-TiOa) ______ 0

Ap [3(CaO'P2O8 'CaF2 )] 1.3

Fr (CaF2 ) __________ 0.1

2 Salic ________ 46.8

2 Femic _______ 53.2 

Differentiation index:

_____(Q + Or + Ab + Lc+Ne) 27.7

Olivine basalt 

aa flows

16 

215C

17

223

Olivine 

basalt

in palagonlte

18 

251C

Quartz 

trachyte

19 

252-3

Olivine

basalt

pillow

lava

20

216

Olivine

basalt

cinder

cone

21

217

Latite 

lens in 

breccia

22 

220C

Trachyte 

lava

23 

218-1

Major oxides as

43.12

13.20

2.87

9.09

(11.7)

11.51

11.41

2.80

1.30

.18

.10

3.45

.57

.20

.02

.05

.10

45.4

14.2

5.7

6.5 

(11.6)

9.3 

11.0

2.7 

.93 

.46 

.34

2.2 

.49 

.19 

.05

n.d.

n.d.

47.6

18.0

3.3 

8.3 

(11.3) 

4.6 

8.1 

4.4 

1.7 

1.2 

.44 

.27 

.95 

.21 

.08 

n.d. 

n.d.

14.7

1.8 

1.5 

(3.1) 

.0 

.62 

6.5 

4.5 

.30 

.07 

.17 

.02 

.11 

<.05 

n.d. 

n.d.

44.50

16.07

4.89

7.94

(12.4)

5.22

9.07

4.29

1.52

1.25

.44

3.34

.95

.23

.19

.13

.12

47.6

16.6

10.4 

1.5

(10.7) 

4.1 

7.3 

4.9 

1.7 

.60 

.40 

2.5 

1.9 

.25 

.11 

n.d. 

n.d.

52.37

17.67

6.19

2.50

(8.1)

2.12

5.44

5.72

2.61

1.29

.85

1.84

.62

.27

.19

.15

.13

60.87

17.37

3.21

1.62

(4.5)

.57

1.06

7.53

4.80

1.11

.32

.66

.11

.23

.19

.08

.15

99.97

.05

100.15

.08

99.96

.08

99.88

.08

99.92 99 99 100 100.07 100 99.88 99.80

Minor elements,

.07

.0007

.02

.07

.005

.07

.01

.002

.005

)

.007 

.007 

.05

5 

.003

)

.15 

.05 

.002 

.0002 

.015

0

0

.03 

.0001

5

.007 

.07 

.007 

.001

)

.0005 

.003 

.02 

.05 

.0015 

.003

)

.05 

.02 

.002 

.0002 

.02

0

0

0

.05

.0001

.01

.005

.0015

.003

.0015

.01

.0005

.003

.015

.02

0

.001 [> .1

.015

.003

.0003

.02

0

0

.002

.0007

.07 

5

.0003

.00015

.003

.05

.001

.015

.02 

[>

.003 

0

.0015

.0007 

[>

.007

.0007

.15

.07

.003 

.007 

.005 

.003 

.007

0

.01 

.01 

.003

[> 

.0015

5

.15 

.03 

.003 

.0003 

.03

.03

.0001 

)

.007

.1

.007

.001 

)

.0005

.003

.02

.1 

5

.001 

5

.1

.01

.003

.0003

.02

0

0

0

.1

0

.015

.001

.0002

.001

.003

.01

0

.015 

.02

.005 

.01

.02 

.02

0

.0007 

)

.15 

.007 

.003 

.0003 

.02

0

.0003 

)

.01 

5

.003

.0003

.1

Major oxides, recalculated to 100 percent

43.3

13.2

2.9

9.1

11.6

11.5

2.8

1.3

3.5

.6

.20

46.0

14.4

5.8

6.6

9.4

11.2

2.7

.9

2.2

.5

.19

48.8

18.5

3.4

8.5

4.7

8.3

4.5

1.7

.3

1.0

.22

69.9

14.8

1.8

1.5

0

.6

6.5

4.5

.17

.02

.11

45.3

16.4

5.0

8.1

5.3

9.2

4.4

1.6

3.4

1.0

.23

48.2

16.8

10.5

1.5

4.2

7.4

5.0

1.7

2.5

1.9

.25

53.6

18.1

6.3

2.6

2.2

5.6

5.9

2.7

1.9

.6

.28

61.2

17.7

3.3

1.7

.6

1.1

7.7

4.9

.7

.11

.23

Normative

0

7.7

6.8

19.9

0

9.0

.08

0

13.6

9.5

2.9

13.5

4.7

4.2

0

6.6

0

0

1.4

.2

0

5.6

21.2

24.2

0

1.1

0

0

11.6

8.9

1.5

10.2

1.9

8.4

0

4.2

0

0

1.2

0

0

10.0

28.4

25.1

0

5.4

0

0

4.1

1.9

2.1

6.9

8.2

4.9

0

.6

0

0

2.4

0

14.0

26.7

50.8

0

0

0

0

3.9

1.2

0

2.3

0

0

.7

0

.3

0

0

.05

0

0

9.2

24.1

21.0

0

6.4

.2

0

7.5

4.9

2.1

5.8

2.7

7.2

0

6.5

0

0

2.3

.2

0

10.2

42.0

18.5

0

0

0

0

1.5

1.6

0

6.1

0

0

10.5

3.8

1.4

0

4.6

0

0

15.8

47.2

15.8

0

.6

.3

0

2.9

2.5

0

2.0

0

3.7

3.8 

3.6 

0 

0

1.5 

.2

0

28.9

58.6

0

0

2.8

.1

.4 

1.5 

1.3 

0

.1 

0 

4.1

.3 

1.3 

0 

0

.3

.3

43.5

56.5

23.5

52.0

48.0

68.9

31.1

43.8

91.5 

8.5

91.5

60.9

39.1

39.7

70.6

29.4

52.1

79.8

20.2

63.7

90.4 

9.6

90.2
HALLETT VOLCANIC PROVINCE C51

rocks of Hallett Volcanic Province, other than Hallett Peninsula

Geol. Survey laboratories, Denver, 1965: major oxides by Ellen S. Daniels by gravimetric methods, and 6-step semiquantltatlve spectrographic 

major oxides by X-ray fluorescence and colorimetrlc methods by P. L. D. Elmore, Samuel Botts and Lowell Artls, and 6-step semiquantiHf, Hg, In, Li, Pd, Pr, Pt, Re, Sb, Sm, Ta, Te, Th, Tl, V, and W]

Daniell 

Peninsula

Olivine 

basalt

flow

24

277

Adare Peninsula

Olivine basalt

flows

25

232B

26

240B-1

Olivine basalt

pillows

27

233F

28

233D

Palogonite

29

233G

Latite

dike

30

233A

Basanite

pillow

31

226A

Small Islands

Olivine basalt

flows

32

227B

33

225A

Olivine 

basalt

scoria

34

225C-2

analyzed, weight percent

44.70

16.17

8.10

5.22

(12.5) 

4.92

8.98

3.93

.75

1.17

.68

3.67

.62

.19

.87

.07

.09

100.13

.06

100.07

46.09

15.26

7.11

4.95

(11.4) 

7.46

9.78

3.71

1.57

.23

.12

2.71

.67

.21

.10

.06

.09

100.12

.05

100.07

41.77

14.28

4.64

8.26

(12.4) 

8.56

11.74

3.41

1.39

.74

.47

3.73

.68

.21

.14

.08

.10

100.20

.06

100.14

40.34

13.87

9.10

3.96

(12.2) 

6.53

10.96

3.47

1.02

2.02

1.90

3.61

.70

.20

2.02

.59

.06

100.35

.16

100.19

42.64

14.46

5.54

7.92

(12.9) 

7.37

11.50

2.99

.96

.99

.51

4.01

.71

.20

.22

.05

.09

100.16

.05

100.11

38.2

13.0

5.8

3.4

10.5

9.0

3.1

1.4

2.4

2.5

2.5

.63

.16

7.0

n.d.

n.d.

__

 

100

49.0

18.0

6.5

2.1 (t:2>

5.7

4.8

2.7

2.0

1.8

1.8

.77

.27

.86

n.d.

n.d.

 

99

41.18

13.52

3.57

8.86

(12.1) 

9.46

12.25

4.43

1.69

.09

.07

3.47

.99

.22

.02

.34

.11

100.27

.13

100.14

46.65

15.64

3.24

7.61

(10.5) 

7.32

9.86

4.27

1.53

.11

.05

2.81

.60

.21

.02

.10

.09

100.11

.06

100.05

44.94

15.59

2.25

8.86

(10.9) 

7.61

10.48

3.87

1.33

.16

.17

2.98

.66

.19

.65

.11

.09

99.94

.07

99.87

46.21

16.41

3.88

7.16

(10.7) 

6.01

9.61

4.30

1.55

.34

.27

2.90

.74

.21

.01

.20

.10

99.90

.08

99.82

weight percent

.05

0

0

.005

.005

.007

.002

.003

0

.005

.007

.002

0

.002

0

.15

.1

.002

.0003

.02

for components

45.9

16.6

8.3

5.4

5.1

9.2

4.0

.8

3.8

.6

.20

.1

0

0

.005

.03

.01

.003

.007

0

.007

.01

.01

0

.003

0

.15

.03

.002

.0003

.02

.05

0

0

.005

.03

.01

.002

.007

0

.007

.007

.01

0

.003

0

.1

.05

.002

.0002

.02

.03

0

0

.005

.02

.01

.002

.007

0

.005

.007

.01

0

.002

0

.1

.03

.002

.0002

.01

.03

0

0

.005

.02

.01

.002

.007

0

.007

.01

.01

0

.003

0

.1

.05

.002

.0002

.015

.03

0

0

.003

.05

.007

.0015

0

0

.003

n.d.

.02

.0001

.002

0

.07

.015

.002

.0002

.015

.1

.0005

.05

0

.0005

.0003

.002

.03

.001

.01

.02

0

.0007

.0005

0

.1

.007

.003

.0003

.03

.07

0

.015

.005

.05

.01

.003

.01

0

.01

.02

.02

0

.003

0

.2

.05

.003

.0003

.02

.07

0

0

.005

.03

.01

.003

.007

0

.01

.01

.01

0

.002

0

.15

.05

.002

.0003

.02

.07

0

0

.005

.03

.01

.003

.007

.001

.007

.01

.02

0

.002

0

.15

.05

.002

.0003

.02

.1

0

0

.007

.05

.015

.007

.015

0

.015

.01

.02

0

.003

0

.3

.07

.005

.0007

.03

listed, weight percent

46.2

15.3

7.1

5.0

7.5

9.8

3.7

1.6

2.7

.7

.21

42.3

14.5

4.7

8.4

8.7

11.9

3.5

1.4

3.8

.7

.21

42.7

14.7

9.6

4.2

6.9

11.6

3.7

1.1

3.8

.7

.21

43.3

14.7

5.6

8.1

7.5

11.7

3.0

1.0

4.1

.7

.20

43.6

14.8

6.6

3.9

12.0

10.2

3.5

1.6

2.9

.7

.18

51.8

19.0

6.9

2.2

3.2

6.0

5.1

2.9

1.9

.8

.29

41.1

13.5

3.6

8.9

9.5

12.2

4.4

1.7

3.5

1.0

.22

46.7

15.7

3.2

7.6

7.3

9.9

4.3

1.5

2.8

.6

.21

45.4

15.8

2.3

9.0

7.7

10.6

3.9

1.3

3.0

.7

.19

46.6

16.5

3.9

7.2

6.1

9.7

4.3

1.6

2.9

.8

.21

composition

0

4.5

33.6

25.2

0

0

.1

0

6.6

5.9

0

4.6

0

7.0

3.5

7.2

0

0

1.5

.1

63.5

36.5

0

9.3

24.2

20.7

0

3.7

.1

0

8.7

8.4

0

7.2

0

8.8

1.1

5.2

0

0

1.6

.1

58.0

42.0

0

8.3

6.5

20.1

0

12.0

.1

0

14.1

10.2

2.7

8.0

2.3

6.8

0

7.2

0

0

1.6

.1

47.0

53.0

0

6.4

17.3

22.9

0

5.0

1.0

0

12.4

10.7

0

4.6

0

3.2

7.5

7.3

0

0

1.8

.1

52.6

47.4

0

5.8

16.8

23.8

0

4.6

.1

0

12.1

9.1

1.8

6.7

1.5

8.2

0

7.7

0

0

1.7

.1

51.0

49.0

0

9.4

10.0

19.9

0

10.8

0

0

11.0

9.5

0

14.2

0

4.8

3.3

5.4

0

0

1.7

0

50.0

50.0

0

16.9

40.3

20.7

0

1.4

0

0

1.6

1.4

0

4.6

0

2.6

5.1

3.6

0

0

1.9

0

79.3

20.7

0

5.2

0

13.3

3.7

18.9

.6

0

16.9

11.6

3.9

8.4

3.1

5.2

0

6.6

0

0

2.3

.1

41.8

58.2

0

9.0

19.9

19.4

0

8.4

.2

0

10.5

7.0

2.7

7.9

3.4

4.7

0

5.3

0

0

1.4

.1

56.9

43.1

0

7.9

15.4

21.9

0

9.1

.2

0

10.8

6.7

3.5

8.7

5.0

3.3

0

5.7

0

0

1.6

.1

54.6

45.4

0

9.2

23.1

21.8

0

6.5

.3

0

8.7

5.9

2.2

6.5

2.6

5.7

0

5.5

0

0

1.8

.1

61.0

39.0

38.1 37.2 26.8 28.6 27.2 30.2 58.6 27.9 37.4 32.5 38.9
C52 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

rock is anhedral opaque granules. Large cylindrical plug of 

trachyte intrusive into palagonite breccia, east side of Hallett 

Peninsula (fig. 14).

14 (247C). Quartz trachyte (or quartz-poor rhyolite). Paleolive holocrystalline rock, speckled by lighter areas and by 

small dark spots. About 5 percent is of euhedral anorthoclase 

phenocrysts as much as 4 mm long which show no grid 

twinning. One percent of the rock is of mafic phenocrysts 

pseudomorphs of fibrous dusky yellow amphibole after prismatic pyroxene or amphibole are irregularly transformed to 

very poikilitic and irregular amphibole which is pleochroic to 

moderate green. The very fine grained groundmass consists of 

subhedral laths of sanidine dispersed in a raggedly anhedral 

mosaic of alkali feldspar and subordinate quartz, and containing tiny shreds of moderate-green amphibole and opaque granules. Irregular small areas the dark spots seen in hand 

specimen of the groundmass have been largely replaced by 

opaque minerals and a little amphibole, these mafic materials 

being printed across the fabric of the rock and replacing 

quartz and anorthoclase but not albite. Sparse veinlets consist of quartz, subordinate amounts of calcite, and locally a 

radial-structured zeolite. Large irregular bulbous mass of 

trachyte, east side of Hallett Peninsula (fig. 14).

Small masses of volcanic rocks of the mainland 

Nos. 15-19 (table 3)

15 (210B). Olivine-diopside basalt. Dense medium-dark-gray 

rock containing aggregates to as much as 5 mm across of 

greenish-yellow olivine. About 5 percent of the rock is of fragmental phenocrysts of colorless olivine, and less than 1 percent 

is of fragments of labradorite. The groundmass is an extremely 

fine grained mass of poorly shaped laths of plagioclase shorter 

than 0.1 mm, granules of greenish clinopyroxene about 0.01 

mm in diameter, opaque granules, anhedral low-relief grains 

(anorthoclase? G. M. Fairer reported the presence of this 

mineral from X-ray analysis), and much brownish "chlorophaeite" and "nontronite." Plug of basalt intrusive into Paleozoic granodiorite, west side of Moubray Bay (fig. 17).

16 (215C). Olivine basalt. Microvesicular dark-gray rock, 

studded by greenish-yellow olivine phenocrysts several millimeters long. These phenocrysts are variably resorbed but are 

unaltered, and compose about 2 percent of the rock; an additional 10 percent is of groundmass olivine granules and microphenocrysts. Seriate phenocrysts of zoned augite (cores pleochroic in light olive, rims in dusky yellow) form 1 percent of 

the rock and are mostly smaller than 0.5 mm. About 40 percent 

of the rock consists of groundmass clinopyroxene, as brownish 

granules smaller than 0.1 mm, and 10 percent consists of 

poorly shaped laths of calcic plagioclase shorter than 0.1 mm. 

Opaque granules about 0.005 mm in diameter are abundant. 

The rest of the groundmass is nearly isotropic, and its constituents were not identified optically. Small remnant of volcanic rocks near Trafalgar Glacier (fig. 4).

17 (223). Olivine basalt. Medium-gray rock with abundant 

microvesicles. A nearly opaque groundmass encloses seriate 

phenocrysts of olivine, nearly colorless augite, and sodic labradorite, all mostly smaller than 1 mm. Aa breccia, west of 

Daniell Peninsula and north of Mount Prior (fig. 14), collected 

by D. F. Crowder.

18 (251C). Olivine basalt. Dense medium-gray rock. About 

20 percent of the rock consists of seriate microphenocrysts> and 

groundmass laths of labradorite, and 2 percent consists of

olivine microphenocrysts and granules. The remainder is a 

nearly opaque and extremely fine grained mass of opaque dust, 

clinopyroxene microlites, low-birefringence minerals, glass, and 

unidentified materials. G. M. Fairer reported X-ray recognition 

of anorthoclase and sanidine as well as of several of the optically identified minerals. Lens of lava in small mass of 

palagonite breccia, south of Tucker Glacier (fig. 4) ; collected 

by D. F. Crowder.

19 (252-3). Quartz trachyte (or quartz-poor rhyolite). 

Vesicular light-gray clinkery rock with strong flow structure. 

Seriate phenocrysts of anorthoclase (small 2V, weak grid 

twinning) and sparse microphenocrysts of green clinopyroxene 

(large 2V, p<v, aegerine-augite?). Groundmass consists of 

tiny tablets of albite, anhedra of anorthoclase(?), microlites 

of green clinopyroxene, opaque dust, and glass which presumably contains occult quartz and alkali feldspar. Small area of 

volcanic rocks capping ridge of Paleozoic rocks, near Trainer 

Glacier (fig. 4) ; collected by D. A. Coates.

Coulman Island 

Nos. 20-23 (table 3)

20 (216). Olivine basalt. Dense aphanitic dark-gray rock. 

No phenocrysts. About 3 percent of the rock consists of olivine 

granules and prisms, smaller than 0.4 mm, variably iddingsitized; and about 20 percent consists of laths of labradorite 

(about Aneo), mostly shorter than 0.1 mm. The remainder consists of pyroxene microlites and opaque dust densely clouding 

isotropic glass. Sparse microvesicles are lined by a radial 

fibrous nearly isotropic zeolite, which has negative relief and 

is length-slow apophyllite? Nodular lava in palagonite breccia, 

north end of island (fig. 6).

21 (217). Olivine basalt scoria. Grayish-red cinder with a 

glassy skin. Ten percent of the rock consists of seriate plagioclase (about Anw), reaching 7 mm long but mostly shorter than 

1 mm, down to 0.03-mm laths in the groundmass; 2 percent 

consists of partly altered colorless olivine microphenocrysts; 

and less than 1 percent is of clinopyroxene microphenocrysts. 

The remainder is a nearly opaque mass clouded darkly by 

opaque dust and granules and green pyroxene microgranules. 

Cinder cone, west flank of summit volcano (fig. 6).

22 (220C). Latite. Dense medium-gray aphanitic rock. 

Sparse phenocrysts of andesine and of pale-olive augite are 

set in a nearly holocrystalline but very fine-grained groundmass. The groundmass consists of 0.1-mm anhedra of alkali 

feldspar (anorthoclase?), which comprise perhaps 50 percent 

of the rock, and are crowded densely with subhedra and 

euhedra of the other minerals. These consist of 0.1-mm subhedral laths of calcic oligoclase, about 20 percent of the rock; 

minute prisms of slightly greenish clinopyroxene, about 10 percent; tiny prisms of iddingsite, presumably pseudomorphs of 

an iron-rich olivine, about 7 percent; 0.01-mm granules of 

opaque minerals, about 5 percent; nearly opaque pseudomorphs 

after biotite or hornblende, about 1 percent. There is a little 

glass, carbonate, and clay(?). Nodular lava lens in breccia, 

west side of island (fig. 6).

23 (218-1). Trachyte. Greenish-gray rock displaying bright 

sheen on breaks parallel to the groundmass flow structure; 

studded with white phenocrysts. About 10 percent of the rock 

consists of euhedral grid-twinned anorthoclase phenocrysts,' 

more or less clustered, as much as 5 mm long. The groundmass 

is dominated by very thin laths, typically 0.3 mm long and 

0.01-0.02 mm thick, of oligoclase and sanidine, in spectacularly
HALLETT VOLCANIC PROVINCE C53

oriented swirled parallelism. The two groundmass feldspars 

are so similar in appearance and occurrence that their proportions cannot be estimated closely, but the sanidine is 

dominant; it ,has straight extinction in sections perpendicular 

to 010 and has entirely negative relief. The oligoclase has 

nearly straight extinction, albite twinning, and negative to 

slightly positive relief: the composition is near Anao. Subhedral 

microphenocrysts and tiny granules of clinopyroxene (aegerineaugite? pleochroic from 2'=light olive to a?'=yellow green; 

x /\ c about 30°) make up about 4 percent of the rock; partly 

iddingsitized granules of greenish-yellow olivine make up 

about 1 percent; and microphenocrysts of opaque-rimmed 

brown biotite make up less than 1 percent. Interstitial analcite 

makes up about 5 percent of the rock, and opaque granules 

several percent. The optical identification of analcite and sanidine was confirmed by X-ray powder study by G. M. Fairer. 

North rim of Coulman caldera (fig. 6).

Daniell Peninsula 

No. 24 (table 3)

24 (277). Olivine basalt. Massive medium-dark-gray rock. 

Sparse phenocrysts of labradorite and olivine, the latter now 

mostly iddingsite. The groundmass is dominated by seriate 

laths of plagioclase (about 50 percent of the rock) ; the larger 

laths, typically about 0.5 mm long, are of labradorite with 

narrow rims of andesine, whereas the smaller laths, typically 

0.1 mm, are of andesine alone. About 5 percent of the groundmass consists of granules of iddingsite, 15 percent consists of 

granules and microprisms of clinopyroxene, and 10 percent 

consists of 6paque granules. Interstitial and very poikilitic 

alkali feldspar (anorthoclase?) makes up about 15 percent. 

Veinlets of calcite cut the rock. Massive basalt lava, east side 

of peninsula (fig. 6).

Adore Peninsula 

Nos. 25-30 (table 3)

25 (232B). Olivine basalt. Microvesicular dark-reddish-gray 

rock speckled by phenocrysts of greenish-yellow olivine, black 

augite, and white plagioclase. Seriate phenocrysts, augite being 

dominant over either olivine or plagioclase, compose about 20 

percent of the rock an unusually large amount for a basalt 

in this province. The augite phenocrysts are euhedral to fragmental and are dusky yellow and almost nonpleochroic; a few 

grains, not otherwise obviously different from the others, have 

vermicular reaction rims. Olivine is fresh and also includes 

both euhedra and fragments. Plagioclase (middle labradorite) 

phenocrysts are poorly shaped and include both corroded and 

fragmental grains; some grains display around parts of their 

margins narrow inclusion-clouded reaction rims, outside of 

which are narrow rims of uniform plagioclase more calcic 

than that of the rest of the crystal. The microvesicular groundmass is darkly clouded by opaque dust and granules; labradorite laths, augite euhedra, and olivine granules are recognizable, 

and much glass appears to be present. Lava flow, Adare 

Saddle (fig. 17).

26 (240B-1). Olivine basalt. Dense medium-dark-gray rock 

studded by phenocrysts that are mostly small. Ten percent of 

the rock consists of seriate phenocrysts of augite, weakly 

pleochroic in dusky yellow, as much as 8 mm in diameter; 

there are fewer phenocrysts of olivine and magnetite. The 

groundmass contains much brown glass, in which are set 0.1-

mm laths of calcic plagioclase, which constitutes only about 

10 percent of the rock, and more abundant granules of clinopyroxene and opaque minerals. Lava flow, crest of peninsula 

near north end, altitude 350 m (fig. 17).

27 (233F). Olivine basalt. Aphanitic medium-gray rock. 

Sparse microphenocrysts of olivine and augite and tiny laths 

of calcic plagioclase are set in a nearly opaque groundmass of 

opaque minerals, glass, and unidentified materials. Only a few 

percent of the rock consists of identifiable mineral grains. 

Microvesicules are filled with calcite and analcite. Chilled margin of 3-m pillow in palagonite breccia, Cape Roget (fig. 17).

28 (233D). Olivine basalt. Aphanitic medium-dark-gray 

rock. Seriate microphenocrysts of fresh colorless olivine and 

pale-olive augite each constitute a few percent of the rock. The 

groundmass is very fine grained, but holocrystalline, and consists of about 30 percent of 0.05-mm laths of calcic plagioclase, 

about 40 percent of 0.01-mm prisms of clinopyroxene, 10 percent of opaque granules smaller than 0.01 mm, and about 10 

percent of low-birefringence low-relief material which presumably includes alkali feldspar and nepheline. The ratio of 

pyroxene to plagioclase is higher than is suggested by the 

normative composition. Interior of 1-m nodule of lava in 

palagonite breccia, Cape Roget (fig. 17).

29 (233G-1). Olivine - basalt palagonite tuff. Earthy 

yellowish-gray obscurely bedded rock strewn liberally with 

clasts to a few millimeters in diameter of medium-gray basalt. 

In thin section the rock is seen to consist of brown clasts of 

varied hydrated glassy basalts, which differ greatly in their 

textures and their proportions of olivine, augite, magnetite, 

and plagioclase. Most clasts have a yellowish-orange nearly 

isotropic matrix. Interstices between clasts are filled mostly 

with calcite, which also comprises abundant grains within 

many clasts. Bedded palagonite tuff, Cape Roget (fig. 17).

30 (233A). Latite. Aphanitic light-olive rock with abundant 

small flow-alined vesicles. Sparse small phenocrysts of paleolive augite, brown amphibole, andesine, and magnetite are set 

in a microvesicular groundmass that displays strong trachytic 

flow orientation of feldspar laths. About 55 percent of the rock 

consists of andesine laths, typically 0.02 X 0.3 mm. Iddingsite 

granules, needles and granules of clinopyroxene, and opaque 

granules make up about 5 percent each. Interstitial material 

makes up about 25 percent and appears to consist of anorthoclase, analcite, calcite, and glass. Vesicles are variously empty, 

lined with analcite, and lined with analcite and filled with 

calcite. Center of dike 2.5 m wide, that cuts palagonite 

breccia, Cape Roget (fig. 17).

/Small islands 

Nos. 31-34 (table 3)

31 (226A). Basanite. Vesicular dark-gray rock. About 12 

percent consists of fresh colorless olivine, mostly as seriate 

phenocrysts and microphenocrysts, but partly as groundmass 

granules. Pale greenish-yellow augite phenocrysts make up 

3 percent of the rock, and dusky-yellow clinopyroxene prisms 

and granules, mostly 0.02-0.1 mm long, make up 55 percent. 

Opaque granules make up another 5 percent. Twenty-five percent consists of mostly clear interstitial yellow and brown 

glass. No feldspar or feldspathoid is present in crystalline 

form; the rock is named a basanite because the norm contains 

23 percent nepheline plus leucite, demonstrating that the glass 

must be mostly of feldspathoidal composition. Rubbly lava 

flow, south end of Possession Island (fig. 17).
C54 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

32 (227B). Olivine basalt. Grayish-black very vesicular 

rock. About 10 percent consists of olivine phenocrysts and 

microphenocrysts, the largest 5 mm in diameter; the mineral 

is unaltered, although some phenocrysts have rims of granular 

augite. Phenocrysts and microphenocrysts of pale-olive augite 

constitute 20 percent, and there are rare microphenocrysts of 

opaque-rimmed brown hornblende and sparse megacrysts of 

hornblende to 2 cm long. The groundmass consists of plagioclase laths, mostly shorter than 0.1 mm, and interstitial glass 

crowded and made dark by minute granules of clinopyroxene 

and opaque minerals. The thin section contains an autolithic(?) inclusion of olivine-augite rock. Vesicles are empty. 

Lava flow, McCormick Island (fig. 17).

33 (225A). Olivine basalt. Dark-gray vesicular rock. Augite 

phenocrysts constitute about 15 percent of the rock; augite is 

dusky yellow with or without pale-yellowish-brown rims. Colorless phenocrysts of fresh but partly resorbed olivine make up 

10 percent. The groundmass consists of laths of labradorite 

(about 30 percent), prisms of pale-yellowish-brown clinopyroxene (about 20 percent), granules of olivine (5 percent), 

octahedra of magnetite (about 3 percent), plates of ilmenite 

(about 1 percent), and interstitial glass. Lava flow, Foyn 

Island (flg. 17).

34 (225C-2). Olivine basalt. Dark-gray scoria. Phenocrysts 

of olive augite and fewer phenocrysts of olivine are strewn in 

a microscoriaceous groundmass which appears almost opaque 

at low magnification. At high magnification, the groundmass 

is seen to contain plagioclase microlaths, pyroxene granules, 

alkali feldspar, glass, and abundant opaque dust and granules. 

Cinder from near summit of Foyn Island (flg. 17).

CHEMISTRY

Thirty-four specimens of volcanic rocks from the 

Hallett province were analyzed chemically (tables 2, 

3). Specimens chosen represent a broad compositional 

spectrum of fresh, hydrated, and oxidized rocks.

MAJOR OXIDES

The chemical analyses define the volcanic province as 

one dominated by sodic basalts and containing subordinate felsic rocks that range from extremely sodic 

phonolite to relatively potassic quartz trachyte.

The highly alkaline character of most of the rocks 

is illustrated by figure 33. Potassium and sodium increase together in most rocks analyzed. Most of the 

basaltic rocks have between 3 and 5 weight-percent of 

Na2O and between 1 and 2 percent of K2O, the ratio 

between these oxides being typically about 2.5:1. The 

analyzed trachytes have between 5 and 8 percent Na2O, 

and 3 and 5 percent K2O, and a ratio of Na2O to K2O 

near 2:1. The quartz trachytes are in general the most 

potassic rocks sampled, having about 5 percent K2O 

and 6-7 percent Na2O, and they have the lowest ratio 

of sodium to potassium in the suite. The most sodic 

rocks are the two phonolites,, each of which has more 

than 10 percent Na2O, and 3-4 percent K2O. The 

trachytes and quartz trachytes contain between 8 and

Quartz trachyte A: j / ]

\^x/ / j- Trachyte

d7 ^/ Pho

yte 

nolite \^/

Basaltic rocks

2 4 6 8 10 

Na2 0, IN WEIGHT PERCENT

12

FIGUBE 33. Contents of KaO and NaaO In the volcanic rocks. Weightpercent amounts from analyses recalculated anhydrous, tables 2 

and 3; two analyses of hydrated tuffs are omitted. Dots, offshore 

volcanic rocks ; x's, mainland volcanic rocks.

13 percent Na2O + K2O, the phonolites as much as 

15 percent.

The "differentiation index" the sum of the normative percentages of quartz, orthoclase, albite, leucite, 

and nepheline (tables 2 and 3) provides a useful 

measure of the gross composition of these alkaline 

rocks, although the genetic connotation of the term 

"differentiation index" is certainly erroneous in many 

rock suites. The major elements, of course, show a 

strong correlation with this index, as a correlation is 

forced by the calculation. The differentiation index is 

an expression of the amounts of silicon, sodium, and 

potassium in the rocks, so those elements necessarily 

correlate positively with it; and as magnesium, iron, 

and calcium are omitted from the index, they necessarily correlate negatively with it. No major-oxide variation diagram is presented here incorporating the 

differentiation index, because so much of the correlation is an artifice of the calculations; but the relationships with MgO and total iron are illustrated in 

figures 34 and 35.

Among the individual major elements, magnesium, 

the most refractory, provides the best single indication 

of the bulk composition of the rocks. Figure 34 is a 

magnesia-variation diagram of the analyses from the 

Hallett province. Most of the other oxides show nearly 

linear positive (FeO, TiO2 , CaO) or negative (SiO2 , 

Na2O, K2O) correlations with MgO within the range 

MgO=0-5. For MgO>5, correlation zones with CaO 

and Na2O have gentler slopes, and correlations with 

SiO2 , total iron, TiO2 , and K2O are poor.

The degree of oxidation of iron in the volcanic rocks 

(fig. 35) varies widely but is mostly high. From 50 to 

90 percent of the iron is in the ferric state in all rocks 

having less than 10 percent total iron, which corresponds to the suite having a differentiation index of
HALLETT VOLCANIC PROVINCE C55

65

60

50

Basaltic rocks

10

MgO

20

15

10

10

50

15

WEIGHT PERCENT

MgO

FIGURE 34. Magnesia-variation diagram of chemical analyses of volcanic rocks of the Hallett province. Data, in 

weight percent, from tables 2 and 3; two analyses of h ydrated tuff are not plotted. Dots, offshore volcanic rocks; 

x's, mainland volcanic rocks.
C56 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

x 80

O 

< 60

Trachyte, quartz trachyte, 

and phonolite

Latite

Basaltic rocks

0 5 10 15 

TOTAL IRON AS FeO, IN WEIGHT PERCENT

FIGURE 35. Iron in the volcanic rocks. Differentiation index and 

FezOs are plotted against total iron as FeO. Data from tables 2 

and 3. Two hydrated tuffs are omitted.

more than 56. By contrast, from 20 to 85 percent of 

the iron is ferric in the rocks having higher (10-13 

percent) total iron, but, in this group, the highly oxidized iron is in rocks that are obviously either highly 

differentiated or secondarily oxidized (as, red scoria). 

The AFM ternary diagram (fig. 36) shows the usual 

symmetry of trachyte-and-basalt provinces in having 

a central cluster of analyses of basaltic rocks from 

which trachytes and other felsic rocks trend toward 

the alkali end of the alkali-iron join, and extremely 

mafic rocks trend toward the magnesia corner. The 

Hallett province is unusual, however, in its high proportion of alkalis even in the most mafic rocks. The 

contrasted trends away from the central cluster cannot

Quartz trachyte

MgO

FIGURE 36. Ternary AFM diagram of weight-percent of alkalis, 

magnesia, and total iron in volcanic rocks of the Hallett province. 

Dots, offshore volcanoes; x's, mainland rocks. Data from tables 2 

and 3; two analyses of hydrated tuff are omitted.

be the complementary products of a single process, 

else they would fall on a single straight line. Among 

the models by which the actual summetry could be 

explained is one invoking accumulation of magnesian 

crystals to explain in part the composition of the most 

mafic rocks and separation of calcic and ferromagnesian crystals combined with addition of volatile 

alkalis and ferric iron to explain the least mafic rocks. 

The ternary diagram of calcium, sodium, and potassium (fig. 37) shows, as does figure 33, that the ratio

Na2O

FIGURE 37. Ternary diagram of proportions, by weight, of CaO, 

Na2O, and K2O in volcanic rocks of the Hallett province. Dots, 

offshore volcanoes; x's, mainland rocks. Data from tables 2 and 3; 

two hydrated tuffs omitted.
HALLETT VOLCANIC PROVINCE C57

of potassium to sodium is nearly constant in the mafic 

rocks but is erratically higher in the felsic ones. Varying amounts of volatile transfer of potassium might 

account for the scatter in the felsic rocks. Sodium is 

slightly to markedly dominant by weight hence 

strongly dominant in molecular proportion over 

potassium in all rocks (fig. 33).

The eleven analyses of volcanic rocks of the Hallett 

province given by Harrington, Wood, McKellar, and 

Lensen (1967, p. 69-72) show variations similar to 

those reported here in major elements.

MINOR ELEMENTS

Minor elements also are listed in tables 2 and 3. 

MnO, P2O5 , Cl, and F were determined with the majoroxide analyses, and other minor elements listed were 

determined by semiquantitative spectrographic methods. 2 The differentiation index is used for the abscissa 

against which minor-element concentrations are 

plotted, because most of the major oxides correlate in 

linear fashion with the index.

Four minor components, MnO, P2O5 , Cl, and F, are 

plotted in figure 38. Phosphorus is irregularly high 

in rocks of low differentiation index and falls steeply 

in linear fashion with increasing index in high-index 

rocks; the extreme trachytes contain very little P2O5 . 

Chlorine determinations scatter considerably but on 

the average are lower in the trachytes. Fluorine data, 

by contrast, define a linear increase through a factor 

of about 2 from the mafic basalts to the trachytes. The 

concentration of chlorine in the mafic rocks is very 

high (compare with data summarized by Johns and 

Huang, 1967). The behavior of manganese is unexpected: through most of the range of the rock suite, 

MnO increases with increasing index, although the 

lowest values of MnO are in the three quartz trachytes. 

Manganese thus tends to increase as both total and 

ferrous iron decrease (compare figs. 35 and 38), 

whereas in most igneous-rock assemblages manganese 

and ferrous iron increase together.

2 The spectrographic data contain some analytical biases. The 

analyses made by the two analysts In different laboratories are comparable for some elements but not for others. Similar values were 

reported by both Button and Harris for Ba, Co, Cr, Nd, Ni, Y, Yb, 

and Zr. Button reported generally higher values than did Harris 

for Cu, Ga, Nb, Sr, and V. Harris has much more scatter than does 

Sutton In La determinations. Button detected Be and Mo in only a 

few samples and lead In none, whereas Harris reported those three 

elements in most samples. Harris reported Ce in many more samples 

than did Sutton, but the reverse Is true of Sc. Each analyst has a 

bias for certain numbers; Harris is twice as likely to report a 3 

(that is, 0.3, 0.03, and so forth) as a 7, and Button'Is twice as 

likely to report a 2 or 3 as a 5 or 15. The systematic variations in 

many of the minor elements are great enough to be obvious despite 

these small analytical biases.

Trachyte, 

quartz trachyte, 

Basaltic rocks Latite and phonolite

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0.6

0.5

0.4

0.3

0.2

0.1

0

0.2

0.1

0

0.3

0.2

0.1

0, 20 40 60 80 100

DIFFERENTIATION INDEX

FIGURE 38. Variation diagram of PuGs, Cl, F, and MnO 

against differentiation index for volcanic rocks of the 

Hallett province. Dots, offshore volcanoes; x's, mainland rocks. Data in weight percent, from tables 2 and 

3. Two hydrated tuffs are omitted.
C58 CONTRIBUTIONS TO THE GEOLOGY OF ANTARCTICA

o.i

0.01

0.001

0.1

0.01

0.001

0.01

cc 0.0001

CDO.l

0.01

0.001

0.0001

0.00001

0.1

0.01

0.0001

Ba

Ce

Co

.A..

Cr

0.00001

Cu

20 40 60 80 

DIFFERENTIATION INDEX

100

0.01

0.001

0.0001

0.1

0.01

0.0001

0.1

0.01

o: 0.001

0.01

0.001

0.1

0.01

0.001

0.0001

Ga

La

Nb

Nd

Ni

0.001

0.0001

Sc

20 40 60 80 100 

DIFFERENTIATION INDEX

Trachyte, 

quartz ' 

trachyte,

Basaltic and 

rocks Latite phonollte

0.01

0.001

0.0001

Sr

0.001

0.001

Yb

o.oi

0.001

Zr

20 40 60 80 100 

DIFFERENTIATION INDEX

FIGURE 39. Semilogarithmic variation diagram of minor elements, plotted against differentiation Index, for volcanic rocks of the Hallett 

province. Dashed lines indicate threshold limits of detection by semiquantitative spectrographic analysis; less-than-threshold ("zero") 

determinations are plotted arbitrarily beneath these lines. Data from tables 2 and 3. Two hydrated tuffs are omitted.

Figure 39 is a variation diagram for most of the 

spectrographically determined minor elements. (Four 

elements are not plotted: lead and tin because they are 

reported in so few samples, and beryllium and molybdenum because only one analyst generally reported 

them, and in erratic amounts that do not show systematic variation with rock type.)

The metals cobalt, chromium, copper, nickel, and 

vanadium show the expected negative correlation with 

the differentiation index. These metals increase exponentially with iron and magnesium in the rocks. 

The abundances of chromium range through three 

orders of magnitude, and those of cobalt, copper, 

nickel, and vanadium through about two orders each.
HALLETT VOLCANIC PROVINCE C59

Of the rare-earth and related metals, cerium, lanthanum, neodymium, yttrium, and ytterbium show 

slight to marked increase with increasing differentiation index, and so increase with silicon, potassium, 

and sodium in the rocks. The degree of increase with 

the index decreases roughly with increasing atomic 

weight (in order for the elements listed: La, Ce, Nd, 

Y, Yb), in accord with the conclusions of Haskin and 

Frey (1966). Scandium shows the reverse correlation, 

decreasing markedly with differentiation index, as 

anticipated from its usual association with iron and 

magnesium.

Barium shows a slight increase with differentiation 

index across most of the range but, in the highest 

index rocks, is very erratic, including by far the lowest 

values. Several of the highest-potassium rocks have 

very low contents of barium. (Nockolds and Alien, 

1954, reported similar variation in other alkalinebasalt provinces.) Niobium increases moderately with 

differentiation index, and it presumably is associated 

with titanium, which behaves in similar fashion. 

Gallium (a difficult element to determine spectrographically) shows a slight but irregular increase with 

differentiation index, and a somewhat better correlation with aluminum content. Strontium (the worst 

element listed for spectrographic quantitative determination) decreases slightly with increasing differentiation index, then scatters with erratic low values in 

the highest-index rocks. Zirconium increases irregularly with differentiation index.

PETROLOGIC COMPARISONS

The volcanic rocks of the Hallett volcanic province 

are petrographically and chemically similar to those 

of the McMurdo Sound region of the southern Ross 

Sea (fig. 2, this rept.; Cole and Ewart, 1968; Harrington and others, 1967, fig. 44; Jensen, 1916; Smith, 

1954; my unpub. analyses), and to the volcanic rocks 

of the intervening coastal region (Nathan and Schulte, 

1968).

The broad patterns of major-oxide variations in the 

Hallett province are also similar to those found elsewhere in provinces of sodic basalts and trachytes, as 

in oceanic islands. Figure 40 illustrates the similarity 

in form of the alkali-iron-magnesium ternary variations of the Hallett volcanic rocks to those of rocks 

from several other basalt-and-trachyte provinces.

The similarity of the Hallett rocks to those of other 

basalt-and-trachyte provinces (for example, Tahiti: 

McBirney and Aoki, 1968) suggests that detailed 

petrologic study of the Antarctic suite will demonstrate the existence of two divergent petrologic series,

MgO

FIGURE 40. Ternary AFM diagram of total alkalis, total iron, and 

magnesium for several sodic basalt-and-trachyte provinces. The 

Ross Sea line applies to the Hallett volcanic province (flg, 36, 

this rept.) and to the McMurdo Sound province (Nathan and 

Schulte, 1968, flg. 9). Other lines are from Nockolds and Alien 

(1954, figs. 16-23).

one ranging to quartz syenite, the other to phonolite, 

for rocks representative of these contrasted lines are 

present in the Hallett province.

REFERENCES CITED

Adamson, R. G., and Cavaney, R. J., 1967, Volcanic debrislayers near Mount Melbourne, northern Victoria Land, 

Antarctica: New Zealand Jour. Geology and Geophysics, 

v. 10, no. 2, p. 418-421.

Adie, R. J., 1962, The geology of Antarctica: Am. Geophys. 

Union Geophys. Mon. Ser., no. 7, p. 26-39.

Adie, R. J., ed., 1964, Antarctic geology: Amsterdam, North 

Holland Publishing Co., 758 p.

Alt, David, 1968, Pattern of post-Miocene eustatic fluctuation 

of sea level: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 5, no. 1, p. 87-94.

Anderson, J. J., 1965, Bedrock geology of Antarctica; a summary of exploration, 1831-1962: Am. Geophys. Union Antarctic Research Ser., v. 6, p. 1-70.

Armstrong, R. L., Hamilton, Warren, and Denton, G. H., 1968, 

Glaciation in Taylor Valley, Antarctica, older than 2.7 

million years: Science, v. 159, no. 3811, p. 187-189.

Bakayev, V. G., ed., 1966, Atlas Antarktiki: Glavnoye Upravleniye Geodezii i Kartografii MG SSSR, 225 p.

Bandy, O. L., 1968, Cycles in Neogene paleoceanography and 

eustatic changes: Palaeogeography, Palaeoclimatology, 

Palaeoecology, v. 5, no. 1, p. 63-75.

Bandy, O. L., and Wilcoxon, J. A., 1970, The Pliocene-Pleistocene boundary, Italy and California: Geol. Soc. America 

Bull., v. 81, no. 10, p. 2939-2947.

Behrendt, J. C., 1964, Distribution of narrow-width magnetic 

anomalies in Antarctica: Science, v. 144, no. 3621, p. 993-