LOW GRADE METAMORPHIC ROCKS OF THE RUPPERT AI© HOBBS
COASTS OF MARIE BYRD LAND, ANTARCTICA
by
JOHN FREDERICK BRAND, B.S.
A THESIS
IN
GEOSCIENCES
Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of
MASTER OF SCIENCE
Approved
Accepted
May, 1979 O^Oh'^r ACKNOIMEDGMENTS The writer is indebted to many individuals who have assisted in the preparation of this report. Special thanks are extended to the late Dr. F. .Alton Wade for suggesting the thesis topic and coordinating the scientific efforts of the 1977-19''8 Marie B>T:d Land expedition. He was always available for consultation on matters of general and geologic interest. Thanks are also extended to Dr. John
R. Wilbanks and to Dr. Wesley E. LaMasurier who sensed as expedition leaders. Their knowledge of Antarctic geology obtained from previous expeditions greatly facilitated the 1977-1978 expedition.
Thanks are extended to Dr. Grover E. Mirray, Dr. Necip GUven and Dr. Monzo D. Jacka, members of the thesis committee, fcr their many suggestions and technical assistance. Dr. John P. Brand offered manv suggestions regarding regional structural and stratigraphic patterns.
This investigation was supported by Tlie National Science
Foundation under grant number DPP 715-19150 AOl. TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS ii
ABSTRACT v
LIST OF FIGURES vi
LIST OF PLATES viii aiAPTER
I. INTRODUCTION 1
General Geology of Marie Byrd Land 2
Saunders Coast 5
Ruppert Coast 7
Hobbs Coast 8
Bakutis Coast 8
Nature and Scope of Investigation 8
Physiography and General Geology 9
Ruppert Coast 9
Hobbs Coast 14
II. STRATIGRAPHY 16
Description of Rock Units 16
Ruppert Coast 16
Northern Mount Pearson 16
Southern Mount Pearson 20
Mount Hartkopf 20
Wilkins Nunatak 23
Bailev Nunatak 26
.11 Nickels Rock 29
Hobbs Coast 29
Peacock Peak 29
Navarrette Peak 32
Wallace Rock 33
Stratigraphic Relationships 35
Ruppert Coast 35
Mount Pearson and Mount Hartkopf 35
Wilkins Nunatak and Bailey Nunatak 36
Nickels Rock 37
Hobbs Coast 37
Peacock Peak 37
Navarrette Peak and Wallace Rock 38
Stratigraphic Nomenclature 38
^fount Prince Group 39
V/ilkins Nunatak Group 39
Mount Pearson Group 40
Geologic History 41
III. CONCLUSIONS 43
REFERENCES CITED 46
IV ABSTRACT
Low grade metamorphic rocks exposed on the Ruppert Coast and
Hobbs Coast are classified into two lithostratigraphic units.
Herein the lower portion is named the Wilkins Nunatak Group and the upper portion is termed the Mount Pearson Group. The Wilkins Nunatak
Group consists of a basal sequence of carbonate rocks conformably overlain by continental sediments. The Mount Pearson Group is composed of geosynclinal graywackes and subgraywackes.
During the late Precambrian and early Paleozoic a sha.llow epicontinental sea covered the Ruppert and Hobbs coasts. Shelf carbonate beds which form the basal portion of the Wilkins Nijinatak
Group were deposited upon an eroded complex of amphibolite gneiss. .As the Ruppert Coast and areas farther west were uplifted, the sea retreated eastward and subgraywackes, protoquartzites and arkose conglomerates were deposited, with seeming conformity, upon the carbonate banks. Basinward, the continental sediments graded into thin-bedded sequences of sandstone and shale. By the Ordovician
Period, the entire area was emergent and was subjected to widespread erosion which formed the regional unconformity at the top of the
Wilkins ^-funatak Group. Subsequently, areas west of the Ruppert Coast were uplifted and lithic graywackes, feldspathic graywackes and sub graywackes of the Mount Pearson Group accumulated in a rapidly subsiding basin. As subsidence continued, possibly to depths approaching 10 kilometers, the basal portion of the Wilkins Nunatak
Group was metamorphosed. Granite plutons were emplaced during the
Cretaceous Period. Block faulting occurred during early Tertiary time,
V LIST OF FIGURES
Figure Page
1. Aerial view of large cirque on the eastern flank of Mount McCoy 11 2. Aerial view of cirque along northern margin of Mount Langway 11
3. Aerial view of northern portion of Lewis Bluff 12
4. Surface view of Mount Hartkopf 12
5. Surface view of northern flank of Mount Pearson 13
6. Aerial view of the snow capped eastern margin of the
Zilch Cliffs 13
7. Aerial view of Bennett Bluff 15
8. Coarse-grained feldspathic graywacke from Mount Pearson 15 9. Diastem separating coarse and fine-grained layers within feldspathic graywacke at Mount Pearson 18 10. Contact between volcanic cobble and sand-size matrix of quartz, orthoclase and oligoclase in lithic graywacke from Mount Pearson 18
11. Migearite fragments and oligoclase crystals in volcanic cobbles in lithic graywacke from Mount Pearson 19
12. Microquartz and chlorite in sand-size matrix of lithic graywacke from Mount Pearson 19 13. .Argillite from Mount Pearson containing coarse sand- size quartz and oligoclase grains embedded in a pyrite and mud matrix 21
14. Sericitized quartz pebble in subgraywacke from Mount Pearson 21
15. Fracture filling dolomite being replaced by epidote. actinolite and spinel 77
16. Tremolite-epidote-wollastonite-homblende schist exposed southwest of Mount Hartkopf ,
VI 17. Euhedral tremolite and epidote grains imply that relict calcite and dolomite were first replaced by tremolite and epidote 24
18. Aerial view of northern flank of Wilkins Nunatak 24
19. Lithic graywacke from Wilkins Nunatak 25
20. Subgraywacke from Wilkins Nunatak 25
21. Arkose conglomerate from Wilkins Nunatak 27
22. Subgray^'acke from Wilkins Nunatak 27
23. Protoquartzite from Wilkins Nunatak 28
24. Feldspathic graywacke from Bailey i^?unatak 28
25. Lithic graywacke from Bailey Nunatak 30
26. Feldspathic graywacke from Nickels Rock 30
27. Surface view of isoclinally folded quartz-hornblende- tremolite-biotite schist at Peacock Peak 31
28. Linear micritic calcite and dolomite bands parallel to biotite and tremolite bands in schist from Peacock Peak 31
29. Relict calcite and dolomite replaced by tremolite, hornblende and wollastonite 33
30. Quartz-biotite-muscovite-chlorite schist from Navarrette Peak 33
31. Quartz transecting pre-existing foliation in schist from Navarrette Peak 34
32. Kink banding in schist exposed at Wallack Rock 34
Vll LIST OF PLATES
Plate*
I. Map of Antarctica showing study area.
II. Geologic map of Ruppert and Hobbs coasts.
Ila. Index to location of plates.
III. Geographic provinces of Antarctica.
IV. Geologic map of Mount Pearson and Mount Hartkopf.
IVa. Deformation of bedding by shear.
V. Geologic map of Bailey Nunatak and Wilkins Nunatak.
VI. Geologic map of Nickols Rock.
VII. Geologic map of Mount Prince and Peacock Peak.
VIII. Geologic map of Navarrette Peak.
IX. Stratigraphic interpretation of Ruppert and Hobbs coasts,
*In pocket.
Vlll CHAPTER 1
INTRODUCTION
The area investigated is in the Ruppert and Hobbs coasts of
Marie Byrd Land (Plate I) between 126° and 142° West longitude, and
74°13' and 76°30' South latitude. Complexes of unmetamorphosed sediment and schists of low metamorphic grade crop out in these two areas (Plate II). Tliis report attempts to classify those rock units to interpret their regional stratigraphic and structural patterns, and to place them within a sequence of geologic events.
Geological investigations in Antarctica require work under extremely adverse conditions where personal safety is a matter of foremost consideration. Several well-established facts and operational modes incidental to field work in most of Antarctica warrant notation:
1. Helicopters often land on mountain tops; thus, one may
frequently work topographically downward across
stratigraphic sections.
2. Outcrops are isolated and cannot be traced on foot over
great distances. Geologic reasoning and inference are
necessary when tr>'ing to relate isolated exposures.
3. Time which can be spent on an outcrop is often limited.
For example, one may hastily gather data in subzero
weather while approaching storms loom on the horizon.
4. One must insure that all possible data are colleced in the time available on a particular outcrop for,
normally, an outcrop cannot be revisited.
General Geology of Marie Byrd Land
Because many geologic features, structural events and rock types are continuous throughout the Saunders, Ruppert, Hobbs and Bakutis coasts of Marie Byrd Land, a general, geologic overview of the region is presented herein. Geophysical data indicate that Marie B)n:d Land is a large island extending from the vicinity of Cape Colbeck to the
Bear Peninsula Q^ade and Wilbanks, 1972). If the ice were to disappear, the mountains of Marie Byrd Land would form a chain of islands (Plate III). Isostatic rebound would alter this picture very little (Wade, 1976). These islands are geologically and geomorpho- logically heterogeneous (Lopatin and Orlenko, 1972) and contain a typical continental crustal assemblage of sedimentary/, metamorphic and plutonic rocks 30 to 38 kilometers thick (Ford, 1964). Geophysi cal evidence presented by Wade (1976) indicates that East and West
.Antarctica constitute a continuous segment of continental crust.
Marie Byrd Land is generally considered to be a Paleozoic and
Mesozoic mobile belt. It may be related to the Transantarctic
Mountains and to the .Antarctic Peninsula, but the latter m.ay also be an unrelated geologic province. Adie (1962, 1964) believed that
West .^tarctica, including Marie Byrd Land, is an extension of the
.Andean orogenic province of South America. Others (Klimov, 1964, and Ravich, 1967) postulated that a substantial portion of Marie
Byrd Land, based on lithologic and petrographic studies, is related to the epeirogenic East Antarctic platform. Marie Byrd Land and
East Antarctica may be linked by successive Paleozoic and Mesozoic
eugeosynclinal belts ivrhich formed during the westward accretion of
the East Antarctic platform (Hamilton, 1967). Such a theor/ of
continental accretion may be plausible because West .Antarctica is
generally younger than East Antarctica (Adie, 1962). Wade and
Wilbanks (1972) suggested that the islands of Marie Byrd Land may be
segments of East Antarctica transported to their present position
along transform faults.
Marie Byrd Land may have remained relatively fixed, however, in
its present position throughout its geologic history (Harrington,
1965). DuToit (1937) assigned Antarctica to the central position
of the late Paleozoic Gondwanaland supercontinent and proposed that
during the Paleozoic evolution of Gondwanaland, a major geosyncline
connected South America, southern .Africa, West Antarctica aiid eastern
.Australia. Halpem (1968, 1971) reported that a continuous Devonian-
Trias sic geochronologic province extends from South America to
eastern Australia, paralleling DuToit's "Samfru Geosyncline'' adjacent
to the stable Gondwanaland mass. The postulated former relationship between .Antarctica, South .America, southern .Africa and eastern
Australia may serve as a guide to future mineral exploration in
.Antarctica (Zumberge, 1979).
The geologic history of Marie Byrd Land is recorded in approximately 12,500 meters of eugeosynclinal sediment deposited during the late Precambrian and the early Paleozoic. Two orogenic and three metamorphic episodes are documented in the exposed geologic sequence O^ade and Wilbanks, 1972; Wade, 1972; Griskorov and
Lopatin, 1975; Voronov, 1968; Lopatin and others, 1974; .Adie, 1962; and Frankes, et al., 1971). Eight specific geologic events have been identified:
1. Deposition of a thick sequence of marine sediments, quartz
sands, argillaceous quartz sands, subgraywackes and thin
shale beds on a pre-Riphean (early-late Precambrian)
basem.ent during the late Precambrian-early Paleozoic.
2. Folding, faulting and intrusion of the sequence by
granodiorite plutons during the Ordovician.
3. Progression of geosynclinal and orogenic activity
northward across Marie Byrd Land throughout middle
Paleozoic and early Mesozoic.
4. Folding and metamorphism of the Ordovician volcanic
sequences during the late Paleozoic. Volcanism occurred
on the Bakutis Coast and glaciation was widespread across
West Antarctica during the Permian.
5. Sporadic acidic volcanism in Marie Byrd Land during the
early Mesozoic.
6. Fragmentation of Gondwanaland at the end of the Jurassic
into the continental blocks of .Antarctica, Australia,
Africa and South .America.
7. Intrusion of Marie Byrd Land by granite and granodiorite
plutons during the Cretaceous. 8. Block faulting of Marie Byrd Land during the early
Tertiary and intrusion of alkali basalt complexes during
the Eocene.
9. Initiation of "m.odem" glaciation in the Oligocene.
Saunders Coast
The first detailed geologic studies in Marie Byrd Land were
conducted near the Saunders Coast (Plate I). Though stratigraphic
details have been developed during subsequent expeditions, the basic
concept of the geologic framework of the Saunders Coast has remained
unchanged since first described by Wade (1937), Stewart (1941),
Passel (1945), Wade (1945), and Warner (1945). Two intensely folded
and metamorphosed sequences fonn a sublatitudinal anticlinorium on
the Saunders Coast. The oldest rock exposed is an early Proterozoic
biotite-gneiss and gneiss-migmatite complex which crops out in the
Fosdick Mountains QVilbanks, 1972). These units were intruded by
granite early in the Ordovician (Lopatin and others, 19^4), by
granodiorite late in the Devonian Q^ade and Wilbanks, 1972) and by
granite in the mid-Cretaceous (Wade, 1976).
The gneiss-migmatite and the biotite-gneiss complexes of the
Fosdick Mountains are approximately 5000 meters thick (Griskurov
and Lopatin, 1975). Lopatin and Orlenko (1972) reported that the metamorphic complex in these mountains could be subdivided into lower
and upper complexes. The lower one consists of migmatized garnet
gneiss, sillimanite gneiss and feldspathic quartzite alternating
with biotite gneiss and numerous bands of biotite-rich amphibolite and biotite-plagioclase schist. Regional .metamorphism of a quartz-
rich, pelitic sediment produced the upper biotite-gneiss complex
(Wilbanks, 1972). Mineral assemblages of the gneiss-migmatite and
biotite-gneiss complexes indicate that they have been metamorphosed
to the amphibolite facies.
Wilbanks (1972) proposed that two different metamorphic episodes
produced the physical dissimilarity between the lower and upper
metamorphic complexes of the Fosdick Mountains. In addition, he
noted 1) the lower series contains fold axes which trend northeast,
and 2) the upper complex has fold axes that trend northwest. Defomia-
tion mthin the upper metamorphic complex was syntectonic with regional
granitization in the western Fosdick .Mountains.
Tlie late Proterozoic and early Paleozoic greenschist-graywacke
sequence exposed south of the Fosdick Mountains in the southern
Edsel Ford Ranges has been called the Swanson Formation CWade and
others, 1977). It is a 5000-meter thick sequence of interbedded
arenaceous shale and argillaceous sandstone O^rner, 1945). Late
Precambrian acritarchs and early Cambrian microphytoliths are the
only fossils which have been recovered from the Swanson Formation
(Griskurov and Lopatin, 1975, and Il'tchenko, 1972). Passel (1945) reported quartz grains within this formation to be subrounded and strained. He speculated that the quartz was derived from, a fine grained metaquartzite. .A prevalence of feldspar over quartz in some portions of the Swanson Formation indicates that the original
sediment suffered little decomposition and was buried rapidly (Wade, 1937). Stewart (1941) reported oolitic limestone from Mount
Corey in the eastern portion of the Edsel Ford Ranges. The mineral composition and texture of the sediments suggest they were deposited in a nearshore or lagoonal marine environment (Warner, 1945).
Tne greenschist-graywacke sequence of the Swanson Formation has been folded into broad anticlines and synclines which trend northwest and plunge 30° - 40° Northwest CA'amer, 1945). Folding, low-grade metamorphism and intrusion took place throughout the Ordov:.cian
Period (Lopatin and others, 1974; Wade, 1945). The biotite-gneiss and gneiss-migmatite complex of the Fosdick Mountains is older than the greenschist-grayiv^acke complex of the southern Edsel Ford Ranges
OA^ilbanks, 19"2). Metamorphism of the upper Fosdick Mountain metamorphic complex and the southern Edsel Ford greenschist-gray wacke complex occurred simultaneously in an infrastructure-super structure relationship.
Ruppert Coast
A gneiss-migmatite complex and a younger greenschist-grawacke complex are exposed on the Ruppert Coast (Plate II). Unlike t.he
Saunders Coast, a metavolcanic complex interbedded with .micaceous quartzites rests unconforraably upon the greenschist-grawacke complex (Lopatin and Orlenko, 1972). The T.etavclcanic com.plex is a few kilometers thick and is folded along northwesterly and northeasterly axes (Girkurov and Lopatin, 19"5; and Lopatin and
Orlenko, 19"21. Lopatin and Krylov (1974) isotopically dated the metavolcanic complex as lower Carboniferous. 8
Hobbs Coast
The geologic structure and the rocks of the Hobbs Coast (Plate
II), the Saunders Coast and the Ruppert Coast are similar. .A
gneiss-migmatite complex is present in uplifted fault blocks in the
northern portion of the Hobbs Coast (Lopatin and Orlenko, 1972).
Similar rock t>^es have been observed in the southeastern portion of
the Hobbs Coast and in the Fosdick .Mountains. .A schist-gravwacke
sequence conformably overlies gneiss-migmatite complex; it is
overlain unconformably by metavolcanic rocks on the Hobbs Coast
(Wade and Wilbanl^s, 1972). Lopatin and Krylov (1974) dated the metavolcanic complex isotopically as mid-late Paleozoic.
Bakutis Coast
.A lov/-grade metamorphic complex approximately 5000 meters
thick, and lithically similar to the Swanson Formation, is exposed
on the Bakutis Coast (Plate I). Structures in this com.plex trend
and plunge northwest. In the Kohler Range, northeasterly trending metasediments are covered by metavolcanic rocks Ofede and v/ilbanks,
1972). .High-grade metamorphic complexes which have been intruded by granite are present near the base of the metasedimentary sequence.
Nature and Scope of Investigation
This report describes the results of field and laboratory studies of the unmetamorphosed sedim.entary and schistose complexes of the Ruppert and Hobbs coasts. Betu^een Novem.ber 14 and December 24,
1977, several outcrops on the Ruppert and Hobbs coasts were visited (Plate II). Transportation was provided by UH-IN helicopters flown, by the VXE-6 squadron of the United States Navy. Special attention was given to changes in lithology and to the structural orientations at different outcrops. Field samples were oriented, if possible, so that detailed petrofabric analyses could be conducted in the laboratory. Strike and dip readings were corrected for the magnetic declination by adding 76° East to each reading (American
Geographical Society, 1968).
In the laboratory, all specimens were sectioned and portions of the thin sections were stained for potassium-rich minerals. .A total of 46 thin sections were described petrogranhically with the aid of i I a four-axis universal stage. Mineralogy of the finer-grained { specimens was determined by x-ray powder diffraction methods. The composition of potassium feldspars determined from x-ray data compiled by Van Der Plas (1966). Premetamorphic and metamorphic " ml histories of each sample are based upon thin-section studies. .An j|| extensive search for palynomorphs was conducted, but yielded no Jp positive resialts. All unmetamorphosed sediment has been described according to the procedures of Pettijolm (1957).
Physiography and General Geology
Ruppert Coast
Tliree groups of prominent mountains, rising 400-800 meters above sea level and 100-200 meters above glacial ice, occur on the
Ruppert Coast (Plate II). Cirques are characteristic of the higher peaks (Figures 1 and 2). Flat-topped nunataks adjacent to the 10 mountain peaks are covered by glacial debris (Figures 3 and 4).
Sedimentary rocks crop out at .Mount Pearson and schistose rocks crop out southwest of Mount Hartkopf (Plate II). .An interbedded sequence of feldspathic graywackes, lithic graywackes and argillite are exposed on the northern tip of Mount Pearson; it has been distorted by a northwest-trending shear zone (Figure 5). ^lafic dikes intruded this sequence along the shear zones. Subgraywacke occurs in the southern tip of Mount Pearson; it has been dissected by northeast-trending joints and then intruded by diorite dikes and younger monzonite dikes parallel to the jointing. Tremolite-epidote- wollastonite-hornblende schist occurs in an urjiamed nunatak soutliwest of .Mount Hartkopf. Foliation within the schist strikes east-west and dips north.
Sedimentary rocks are present at Wilkins Nunatak and Bailey
Nunatak (Plate V). Subgraywackes and protoquartzites confomably overlie feldspathic graywackes, lithic graywackes and arkose 31 conglomerate in Wilkins Nunatak; they have been folded into northeast- J trending recumbent folds. Bailey Nunatak contains feldspathic and lithic graywackes which unconformably overlie the sedimentary sequence exposed in Wilkins Nunatak; they strike west-northeast and dip north-northeast.
Feldspathic graywackes, intruded by mafic dikes, occur at
.Nickols Rock (Plate VI). Bedding strikes northwesterly and dips northeasterly. 11
Fig. 1. - Aerial view of large cirque on the eastern flank of Mount McCov.
n
tig. L. Aerial view of circue alon^ northern margin of .Mount Lang^/a^^. 11
Fig. 1. - Aerial view of large cirque on the eastern flank of Mount .McCoy.
il I) •"I
J-1 g . i.. Aerial view of cirque along northern margin of .^loun Lang-'-'a^''. 12
Fig. 3. - Aerial view of northern portion Lewis Bluff. Upper surface has been eroded by glaciation.
Jl tt *••
Fig. 4. - Surface view of Mount Hartkopf Laree boulders are ^lacial erratics. 13
Fig. 5. - Surface view of northern flank of Mount Pearson. Bedding has been deformed by shear. Large mafic dike has intruded the eastern flank.
•I 31
Jl
6. - .Aerial view of the snow capped eastern margin of the Zilch Cliffs.
J 14
Hobbs Coast The Hobbs Coast (Plate II) contains several groups of prominent mountains. Near the Getz Ice Shelf, mountain peaks extend 400 to 800 meters above sea level. Farther inland, elevations of 2000 to 2200 meters above sea level are not uncommon. .^Iany of the mountains are capped by glacial ice (Figure 6) and others are crested by aretes (Figure "). Schistose rocks unconformably overlie large meta-igneous complexes in the western portion of the Hobbs Coast. Quartz-hornblende-tremolite-diopside-wollastonite-biotite schist is exposed in Peacock Peak (Plate VII). Isoclinal folds, \^^ich trend northwesterly, are well developed within the schist. Schistose complexes also occur at Navarrette Peak and Wallace Rock (Plate VIII). Thin laminations of quartz, biotite, muscovite j
and chlorite form the bulk of the schist at both localities. Though these rocks have been deformed by northwesterly-trending » strjctures, the schist exposed at Navarrette Peak has undergone iy more deformation. ^| 15
Fig. ". - Aerial view of Bennett Bluff. Aretes and snow capped cliffs are present along the northern flank.
:i
Fig. 8. - Coarse-grained feldspathic graywacke from Mount Pearson. Oligoclase, quartz and acidic rock fragments occur in Matirx of biotite ,and pyrite. One scale division equals 38 microns. a-IAPTER 2
STR.ATIGRAPHY
Description of Rock Units
Only gross stratigraphic relationships between rock units exposed on the Ruppert and Hobbs coasts can be determined. The discontinuity of outcrops, scarcity of geologic contacts and apparent lack of fossils preclude precise stratigraphic correlations. On January 9,
1979, the writer visited Dr. Joe Guennel, a research palynologist employed by Marathon Oil Company. The writer thought that several genera of palynomorphs ranging in age from late Precambrian through
Devonian were present in these rocks. Organic materials were, indeed, present, but none could be positively identified (Guennel,
1979, personal communication). Accordingly, correlations must be based upon structural relationships, lithic similarities, strati graphic position and relative degree of metamorphism. These are poor criteria, at best, for precise correlation. Structural data Jl .11 "I appear to be valid for local areas only. VJhen interpretations are based upon degree of metamorphism, it is inferred that rocks of higher metamorphic grade were more deeply buried than rocks of lower metamorphic grade. Thus, rocks of higher metamorphic grade are assumed to occupy the lower portion of the stratigraphic sequence.
Ruppert Coast
Northern Mount Pearson
Feldspathic graywackes, lithic grayw^ackes and argillite occur
16 1' in the northern portion of Mount Pearson (Plate IV)• This sequence has been deformed by shearing (Figure 5) which took place oblique to bedding (Plate lA'a) along northwest-trending cleavage surfaces.
The feldspathic graywacke sequence contains both coarse-grained and fine-grained beds which range from two- to four-centimeters in thickness. Grain sizes, within the coarse-grained beds decreases upward toward the fine-grained beds. The coarse-grained fraction contains particles which vary from fine sand to pebble size. Lithically, tlie coarse-grained portion consists of rounded to sub- rounded mugearite fragm.ents; particles of acidic intrusive igneous rocks: and pebbles of orthoclase, oligoclase, and quartz (Figure 3). Mugearite is a term describing a fine-grained rock similar to trachyt in texture, but in which the chief feldspar is oligoclase. Sericite has selectively replaced the acidic intrusive rock fragments. The oligoclase pebbles have undergone more sericitization than the orthoclase pebbles. The fine-grained layers are separated by ^ diastems (Figure 9). Incorporation of fine-grained materials within 51 the coarse-grained strata suggests that the fine-grained layers were deposited before complete lithification of the underlying coarse grained beds. The lithic graywackes contain well-rounded volcanic cobbles embedded in a sand-size matrix of subangular, subrounded and rounded quartz, orthoclase, oligoclase and chert grains (Figure 10). Euhedral oligoclase crystals and mugearite fragr^ents are present within t.he volcanic cobbles (Figure 11). Microquartz and chlorite 18
Fig. 9. - Diastem separating coarse and fine grained layers within feldspathic grawacke at Mount Pearson. Scale division equals 38 microns.
H m .11 I) •:»
Fic^. 10. - Contact between volcanic cobble and 5 an; size matrix of quartz, orthoclase and oligoclase in lithic graywacke from Mount Pearson. Scale division equals 38 microns. 19
Fig. 11. - Mugearite fragments and oligoclase crystals in volcanic cobbles in lithic grayw-acke from Mount Pearson. Scale division equals 33 microns.
it
i)t'
Fig. 12. - Microquartz and cliiorite in sand size matrix of lithic graywacke from ^lount Pearson. Scale division equals 38 microns. 20
which has been extensively replaced by pyrite (Figure 12) compose the finer grained portion of the sand-sized matrix. The argillites consist of subangular, subrounded and rounded chert, quartz and oligoclase grains of coarse sand size embedded in a matrix of quartz, pyrite and mud (Figure 13).
Southern Mount Pearson Metamorphosed subgraywacke, transected by northeast-trending joints, crops out in the southern portion of Mount Pearson (Plate P/). The subgray\\racke consists of quartz pebbles and angular chert fragments embedded in a sand-size matrix of microquartz, biotite and albite (Figure 14). Manv of the albite grains have been extensivelv t
sericitized. Four generations of mineralization can be seen within ^ fractures which transect the rock (Figijre 15). V/hen fracturing first ji
I occurred, the fractures were filled by quartz. The quartz was then ,i
replaced along fracture margins by dolomite. Epidote and actinolite »»i then selectively replaced the dolomite. Finally, spinel replaced J|i ii dolomite that ^vas not previously replaced by epidote and actinolite. '*' The mineral assemblage of calcite, epidote and tremolite in the subgraywackes implies that previous temperatures reached levels characteristic of the albite-epidote-homfels metamorphic facies (Turner, 1968). ^lount Hartkonf Tremolite-epidote-uollastonite-homblende schist is present in a small unnamed nunatak southwest of ^fount Hartkopf (Plate lY]. 21
Fig. 13. - Argillite from Mount Pearson containing coarse sand size quartz and oligoclase grains embedded in a pyrite and mud matrix Scale division equals 24.5 microns.
••I <% !l
Fig. 14. - Sericitized quartz pebble in subgrav wacke from Mount Pearson. Scale division equals 38 microns. 22
Fig. 15. - Fracture filling dolomite being replaced by epidote, actinolite and spinel Scale division equals 10 microns.
>» ;i
Fig. 16. - Tremolite-epidote-v;ollastonite- hornblende schist exposed southwest of Mount Hartkopf. Dark Bands are relict micritic calcite and dolomite. Scale division equals 38 microns.
J lc>
The presence of micritic calcite and dolomite in this rock suggests that it was once a sequence of limestone and dolostone. Limestone
is thought to have coexisted with dolostone because the wollastonite replaced calcite. In several instances, the micritic calcite and dolomite parallel well developed tremolite zones (Figure 16). The parent limestone and dolostone were replaced first by tremolite and epidote, and later by wollastonite and hornblende (Figure 1^).
Based upon the m.ineral assemblage of calcite, dolomite and trem.olite observed in them, the rocks exposed southwest of Mount Hartkopf were
.metamorphosed to the homblende-homfels facies (Turner, 1968).
Wilkins .Nunatak
Two distinctive rock units are exposed on Wilkins Nunatak i
(Plate V). An interbedded sequence of lithic graywackes, feldspathic !' graywackes, subgraywackes and arkose conglomerates occur on the I
;i folds that trend and plunge northeast (Figure 18) and have been "^ intruded by a granitic pluton (Plate V).
The lithic graywackes are characterized by subangular mugearite pebbles embedded in a sand-size matrix of subrounded mugearite and quartz fragments, microquartz, muscovite and chlorite (Figure 19).
Most mugearite fragments and portions of the matrix have been replaced by kaolinite. The feldspathic grawackes consist of subrounded quartz and mugearite pebbles, chert fragments and oligoclase grains embedded in a sand-size matrix of microquartz. 24
Fig. 17. - Euhedral tremolite and epidote grains imply that relict calcite and dolomite were first replaced by tremolite and epidote. Scale division equals 6.4 microns.
"i
?|
Fig. 18. - .Aerial view of northern flank of Wilkins Nunatak. The recumbent folds have been intruded by a granitic pluton.
J 25
Fig. 19. - Lithic graywacke from Wilkins Nunatak .^lugearite pebbles are embedded in a matrix of quartz, muscovite and chlorite. Scale division equals 38 microns.
'I ;!
Fig. 20. - Subsra: wacke from Wi kins Nunatak. Very coarse quartz sand and plagioclase are embedded in a biotite matrix. Scale division equals 6.4 microns. 26 muscovite, chlorite and pyrite. The mugearite fragments and portions of the matri:<: have been selectively kaolinized. The subgraywackes are composed of very coarse quartz sand and plagioclase grains embedded in a biotite matrix (Figure 20). Tlie arkosic conglomerates are .made of subrounded to rounded antiperthite, graphic granite and strained quartz pebbles embedded in a sand-size matrLx of quartz and plagioclase (Figure 21). Cataclastic zones in this unit have been filled by calcite.
A'ery distinctive subgray\\'ackes and protoquartzite are e:q)osed on t.he southern flank of Wilkins Nunatak. The subgraywackes contain subrounded and rounded quartz pebbles and orthoclase grains embedded in a matrix of microquartz and muscovite (Figure 22), The proto quartzites consist of subrounded to rounded quartz pebbles and angular, kaolinized, volcanic rock fragments embedded in a quartz | sand matrix (Figure 23).
jl Bailev Nunatak ? 1 '( Feldspathic and lithic gray\vackes crop out on Bailey Nunatak I|
(Plate V). Bedding within these rocks is not well defined but is sufficient to disclose that they strike east-northeast and dip west- northwest.
The feldspathic graywackes consist of rounded to subrounded mugearite pebbles, quartz pebbles, acidic, intrusive rock fragments and oligoclase grains embedded in a sand-size matrix of quartz, oligoclase, p>Tite and muscovite (Figure 24). Many mugearite pebbles have been kaolinized. 27
Fig. 21. .Arkose conglomerate from Wilkins Nunatak. .Antiperthite, graphic granite and strained quartz pebbles are embedded in a matrix of quartz and plagioclase. Cataclastic zones are crons
Fig. 22. - Subgraywacke from Wilkins Nunatak. The rounded quartz pebble is embedded in a mat IX of microquartz and m.uscovite. Scale division equals 38 microns. 28
Fi2. 2 o Protoquartzite from Wilkins Nunatak Quartz pebbles and Kaolinized volcanic rock fragments are embedded in a matrix of quartz sand Scale division equals 38 microns.
»
;i It
m.- Fig. 24. - Feldspathic graywacke trom Bailey Nunatak. Quart: pebbles and oligoclase grains are embedded in a matrix of microquartz and muscovite. Scale division equals 38 microns. The lithic graywackes are made of subangular quartz pebbles,
oligoclase fragments and acidic intrusive rock fragments embedded in
a sand-size matrix of quartz, calcite, oligoclase, diopside and
chlorite (Figure 25). The mugearite pebbles, other volcanic rock
fragments and portions of the matrix have been selectively kaolinized
Nichols Rock
Feldspathic graywackes, composed of subangular to subrounded volcanic rock fragments which consist predominantly of mugearite
embedded in a matrix of microquartz, biotite and oligoclase
(Figure 26), crop out at .Nichols Rock (Plate VI) . Bedding \\rithin this unit strikes northwest and dips northeast.
Hobbs Coast
Peacock Peak
Quartz-hornblende-tremolite-diopside-wollastonite-biotite
schist crops out on Peacock Peak (Plate \'II). This sequence has been isoclinally folded along northwest trending and plunging axes
(Figure 27). Foliation within this unit strikes northwest and dips northeast.
Micritic calcite and dolomite crystals parallel biotite and tremolite bands within this sequence (Figure 28). Prior to metamorphism, this unit was limestone and dolostone. The limestone and dolostone were replaced first by tremolite, hornblende and wollastonite. .As metamorphism continued, diopside, hedenbergite and grossularite formed (Figure 29). The rocks which crop out on 30
Fig. 25 Lithic graywacke from Bailey Nunatak. Quartz pebbles and mugearite fragments are embedded in a matrix of quartz and calcite. Scale division equals 38 microns.
Fig. 26. - Feldspathic graywacke from Nickols Rock. Oligoclase fragm.ents are embedded in a matrix of quartz, biotite and oligoclase. Scale division equals 58 microns. 31
Fig. 27. - Surface view of isoclinally folded quartz-hornblende-tremolite-biotite schist at Peacock Peak. Note presence of small floating folds. Diameter of lens cap equals 5 centimeters.
Fig. 28. - Linear micritic calcite and doiom.ite bands parallel to biotite and tremolite bands in schist from Peacock Peak. Scale division equals 24.5 microns. Peacock Peak were subjected to temperatures and pressures equivalent to those which form the hornblende homfels facies (Turner, 1968), based upon the assemblage calcite, wollastonite, diopside and grossularite.
Navarrette Peak
Quartz-biotite-muscovite-chlorite schist occurs in .Navarrette
Peak (Plate VIII). This sequence has been folded along northwest- trending and plunging axes; foliation strikes west-northwest and dips north-northeast. Cataclastic deformation is pronounced within this sequence (Figure 30). Based upon the mineral association muscovite, biotite and chlorite, the rocks at Navarrette Peak have been subjected to temperatures and pressures sufficientlv high to develop the greenschist facies (Turner, 1968).
Wallace Rock
Quartz-biotite-muscovite-chlorite schist are exposed at Vv'allace
Rock (Plate VIII). Kink banding is well developed within this unit (Figure 31). Large quartz veins are present in the schist.
The uniform size of the quartz grains in these veins suggests that sandstone dikes developed in the parent rock prior of deformation and metamorphism. Metamorphism to the level of the greenschist facies is demonstrated by the mineral association muscovite, biotite and chlorite (Turner, 1968). 55
Fig. 29. - Relict calcite and dolomite replaced by tremolite, hornblende and wollastonite. Diopside formed as metamorphism continued. Scale division equals 24.5 microns. Specimen fro.m Peacock Peak.
Fig. 50. - Quartz-biotite-muscovite-chlorite schist from Navarrette Peak. Scale division equals 58 microns. 53
Fig. 29. - Relict calcite and dolomite replaced % by tremolite, hornblende and wollastonite. Diopside formed as metamorphism continued. Scale It division equals 24.5 microns. Specimen from Peacock Peak.
Fig. 50. - Quartz-biotite-muscovite-chlorite schist from Navarrette Peak. Scale division equals 58 microns. D 4
rig. 51. - Quartz transecting pre-existin; foliation in schist from Navarrette Peak, Scale t division equals 58 microns.
ii
Fig. 52. - Kink banding in schist exposed at Wallace Rock. Quartz bands mav have been emplac as sandstone dike prior to metanorphisn. Scale division equals 58 microns
#^# (..^* 35
Stratigraphic Relationships
Ruppert Coast
Mount Pearson and Mount Hartlcopf
The feldspathic grayv\'acke, lithic graywacke and argillite in the northern portion of Mount Pearson have been deformed by northwesterly shearing. The mineral constituents and fabric of these rocks have not been altered by metamorphism.
Subgraywackes which crop out in the southern portion of .Mount
Pearson have undergone metamorphism. They have been subjected to shearing in a zone nearly perpendicular to the shear zone in northern Mount Pearson. Mineral assemblages in these rocks indicate
•il that they have been subjected to ten^eratures and pressures *; characteristic of the albite-epidote-homfels facies. I The mass of ^fount Hartkopf consists of granite. This and ' • other granites in the area of study will provide the basis for a report by another investigator. Rocks considered herein crop out in an unnamed nunatak southwest of Mount Hartkopf. The tremolite- I t epidote-wollastonite-homblende schist which occurs there cannot be correlated with other areas in the immediate vicinity on the basis of lithic or structural relationships. However, they have been subjected to temperatures and pressures of the homblende-homfels facies. Linear arrangement of relict micritic calcite and dolomite parallel to tremolite bands suggests that the parent rock v>-as a stromatolitic limestone and dolostone.
.After stromatolitic carbonates formed in the vicinitv of Mount 36 Hartkopf, subgraywackes similar to those exposed in the southern portion of Mount Pearson were deposited unconformably upon the carbonate unit. Feldspathic grayivackes, lithic graywackes and argillites were then deposited conformably upon the basal argillite unit. Thus, a sequence of stromatolitic carbonate overlain by an internally conformable succession of argillite, feldspathic graywacke, lithic gray\\^acke and an upper argillite existed prior to regional metamorphism of this area.
Wilkins Nunatak and Bailey Nunatak ———— ^ The stratigraphic relationships of units exposed at IVilkins Nunatak (Plate V) are readily discemable. Feldspathic graywackes, ^^ J'' lithic graywackes, subgraywackes, and arkosic conglomerates that »• crop out in the northern flank of Wilkins Nunatak are well e.xposed j I at the base of a large recumbent fold. On the southern flank, ; subgraywackes and protoquartzites occur within the crest of the same • •r recumbent fold. Beds on the northern flank occur stratigraphically 31 II below those exposed on the southern flank. The feldspathic and f' lithic graywackes which are exposed in Wilkins Nunatak are more mature than similar units which crop out at Nfount Pearson. Bailey Nunatak (Plate \') is topographically higher and structurally continuous with V.'ilkins Nunatak. This topographic relationship suggests that the sequence at Bailey Nunatak is younger than the sequence at V.'ilkins Nunatak. Further, feldspathic crrayiv-ackes and lithic graywackes at Bailev Nunatak are less mature than those at Ivilkins Nunatak. The difference in maturity of the 37 sediment at each locality may be attributable to subaerial exposure of the sequence at Wilkins Nunatak before the units in Bailey
Nunatak were deposited. Thus, an unconformity may exist between the two units.
The feldspathic and lithic graywackes in Bailey Nunatak can be correlated lithically with similar units which crop out in Mount
Pearson. Both units contain acidic intrusive rock fragments, mugearite fragments and detrital oligoclase grains.
Nickols Rock
Exposures at .Nickols Rock (Plate VI) contain feldspathic graywackes similar to those exposed in Bailey Nunatak. These two localities can be correlated lithically on the basis of mugearite »'
fragments and detrital oligoclase grains. I i
Hobbs Coast
Peacock Peak
II Peacock Peak contains outcrops of quartz-homblende-tremolite- »l diopside-wollastonite-biotite schist which are structurally discordant with exposures in all aforementioned areas. However, they can be correlated lithically with the tremolite-epidote- woliastonite-hornblende schist which crops out in the unnamed nunatak southwest of Nfount Hartkopf. Rocks in both areas contain relict micritic calcite and dolomite, and have similar metamorphic histories. The abundance of quartz, biotite and hornblende within the schist at Peacock Peak and the scarcity of these minerals in 38 similar sequences southwest of Mount Hartkopf suggests that the sequence exposed at Peacock Peak contained more detrital material.
Furtheimore, both units unconformably overlie an amphibolite gneiss complex which crops out at Bennett Bluff and Mount Prince
(Plate VII).
Navarrette Peak and Wallace Rock
Exposures at Navarrette Peak and Wallace Rock (Plate VIII) contain quartz-biotite-muscovite-chlorite schist. In addition to having similar lithologies, these units share common structural elements and metamorphic histories. Foliation within the schist at each locality strikes northwest and dips northeast. Cataclastic
»i deformation is more pronounced in the schist exposed at Navarrette '
Peak. '•
The rocks at Navarrette Peak and Wallace Rock constitute a distinct stratigraphic succession that is structurally related to , the quartz-homblende-tremolite-dioDside-wollastonite-biotite «' schist at Peacock Peak. If it is assumed that Peacock Peak is closer " to the axis of a major northwest-trending anticlinal structure that transects the Hobbs Coast, the schist exposed in Navarrette Peak and Wallace Rock is younger than the schist exposed in Peacock Peak.
Stratigraphic Nomenclature
The low grade metamorphic rocks exposed on the Ruppert and
Hobbs coasts are part of the geosynclinal complex that foms the western portion of .Antarctica. This sequence has been extensivelv 39 folded, metamorphosed and intruded by granitic plutons. Before the full geologic history of these units can be determined, their stratigraphic relationships and regional structural trends must be established. Precursors of the schistose units exposed southwest of Mount Hartkopf and Peacock Peak were deposited unconformably upon an amphibolite gneiss complex which is herein named the Mount Prince Group. Two additional lithologic groupings are proposed for the low-grade metamorphic rocks exposed on the Ruppert and Hobbs coasts. The Wilkins Nunatak Group is the older of the two groups; the Mount Pearson Group is the younger. A regional unconformity separates the two groups and their inferred relationships prior to folding and metamorphism is shown in Plate IX. f/ 'I Mount Prince Group ; ^ It is proposed that the amphibolite gneiss complexes which occur ; on the Ruppert and Hobbs coasts be classified as the Mount Prince '• .1 Group. The proposed type locality is located at .Mount Prince |i 74°56' South latitude and 134°10' West longitude (Plate VII). t Lithic descriptions, structural geology, stratigraphy and metamorphic history of the Mount Prince Group is to be the subject of a report being prepared by other members of the 1977-1978 Byrd Land expedition.
Wilkins .Nunatak Group The Wilkins Nunatak Group contains lithic assemblages exposed in t.he unnamed nunatak southwest of Mount Hartkopf at Peacock Peak, Wilkins Nunatak, .Navarrette Peak and at Wallack Rock. The t>pe 40
locality is at Wilkins Nunatak (75°40' South latitude and 140°12'
West longitude, Plate V, Figure 19). Tremolite-epidote-wollastonite- hornblende schist exposed southwest of Mount Hartkopf and quartz- homblende-tremolite-diopside-wollastonite-biotite schist which crops out at Peacock Peak were once limestones and dolestones which contained stromatolitic algae and were deposited unconformably on the Mount Prince Group. Biotite and quartz within the schist exposed at Peacock Peak imply that the parent rock contained detritus. Thus, the original limestone and dolostone units exposed as schist at Peacock Peak were deposited in deeper water than
limestone and dolostone now exposed as schist southwest at Mount
Hartkopf. Two distinct depositional facies within the original carbonate sequences are herein proposed.
Precursors to the schistose units exposed southwest of .^fount xHartkopf and in Peacock Peak are conformably overlain by lithic grayv/ackes, feldspathic graywackes, subgraywackes and arkose conglomerates. These units are primarily continental sediment.
Basinward to the east, the gvayi^fSicke sequences and arkose conglomerate
interdigitated with sand and shale units now exposed as schist at
Navarrette Peak and Wallace Rock.
Mount Pearson Group
The Mount Pearson Group is a transgressive sequence that unconformably overlies the Wilkins Nunatak Group. The t^'pe locality
is here designated to include those exposures at Mount Pearson
(^5°56' South latitude and 141°05' West longitude, Plate IV, 41
Figure 5). Lithic assemblages exposed at Mount Pearson, Bailey
Nunatak and Nickols Rock are included in the Mount Pearson Group.
The feldspathic graywackes and lithic graywackes in the Mount Pearson
Group contain an abundance of mugearite fragments. Mugearite is commonly derived from oceanic basaltic volcanoes O^iHiams, Turner and Gilbert, 1954). Thus, much of the material deposited as the
Mount Pearson Group could have been derived from oceanic basalts that formed along a subduction zone.
Geologic History
The geologic history of the low-grade metamorphic rocks of the
Ruppert and Hobbs coasts of Marie Byrd Land, .Antarctica, can now be
inferred. A sequence of geologic events is proposed as follows:
1. Deposition of the sedimentary predecessors of the Wilkins
Nunatak Group unconformably upon the .Mount Prince Group
during the late Precambrian and early Paleozoic (Wade
and Wilbanks, 1972).
a. Carbonate banks formed on platforms in a
shallow epicontinental sea.
b. .As the Ruppert Coast and areas farther west
were uplifted, the sea retreated to the east
and sediment was deposited conformably over
the carbonate banks.
2. By the Ordovician Period, the entire area was emergent
(Wade and Wilbanks, 1972).
5. Deposition of the >fount Pearson Group unconformably 42
upon the Wilkins Nunatak Group. a. As uplift continued, volcanic and continental sediments derived from source areas west of the Ruppert Coast were deposited in a subsiding basin east of the Ruppert Coast. b. As this basin subsided, rocks within the lower portion of the Wilkins Nunatak Group were metamorphosed. Mineral assemblages within the schistose units indicate that metamorphism took place at depths approaching 10 kilometers (Tumer, 1968). ,, 4. During the late Paleozoic, the entire sequence was '1; folded (Wade and Wilbanks, 1972). Large scale thrusting took place from east to west across the Hobbs and Ruppert coasts.
II 5. Granitic plutons intruded the sequence during the '
I Cretaceous Period (Wade and Wilbanks, 1972). i 6. Tertiary block faulting occurred. Eocene to Recent alkali basalt complexes intruded the southern and southwestern portion of the Hobbs Coast O^ade and Wilbanks, 1972). 7. Glaciation began in the Oligocene (Wade and Wilbanks, 1972) and has continued to the present day. CHAPTER 5
CONCLUSIONS
Meta-igneous, intrusive and extrusive igneous, metam.orphic
and sedimentary rocks crop out on the Ruppert and Hobbs coasts.
Meta-igneous rocks, intrusive igneous rocks and sedimentary rocks
occur on the Ruppert Coast, whereas meta-igneous, intrusive and
extrusive igneous and metamorphic rocks constitute the stratigraphic
assemblage of the Hobbs Coast. The apparent lithic dissimilarity
between the coastal areas may have been related to differences in
(a) basin configuration at the time of deposition and (b) incipient
metamorphism.
Correlation of the stratigraphic sequences of the Ruppert
Coast and the Hobbs Coast have been based upon lithologic simi
larities, structural continuity and degree of metamorphism. Although
it does not necessarily follow that rocks of comparable ages v;ill be
metamorphosed to the same degree, for purposes of correlation and
in the absence of more valid criteria it is assumed that units which
have been metamorphosed to a higher degree are older than units of
lesser degree of metamorphism. Before the geologic history of such
sequences can be determined, the premetamorphic identities and
depositional habitats of the parent rock must be understood. The
oldest unit considered in this report is a succession of carbonate
rocks which accumulated in an epicontinental sea. These were
deposited on the eroded amphibolite-gneiss complex which herein is
named the Mount Prince Group (see page 39). As the sea retreated
45
• 44 eastwardly across the Hobbs Coast, a regressive sequence of continental sediment was deposited, conformably, upon the carbonate units. Basinward, the continental strata grade into interbedded sandstone and shale. Uplift continued and a regional unconformity truncated the strata of the Wilkins Nunatak Group, which name is herein proposed for the units bounded at the base by the Mount Prince
Group and at the top by the regional unconformity. Following the deposition, uplift and truncation of the Wilbanks .Nunatak Group, the
Ruppert and Hobbs coasts subsided. A sequence of immature geo synclinal sediment, herein named the Mount Pearson Group, was deposited from a westerly source. After deposition of the Mount
Pearson Group, the lower portion of the Wilkins Group underwent metamorphism. Finally, the entire complex was intruded by granite plutons.
Geologic events of the Ruppert and Hobbs coasts can be placed into a relative framework of geologic time. No definitive fossils have been found to date in the exposed rocks of this area. However, portions of the sequence have been dated by radiometric methods.
From information at hand, it appears that the low grade metamorphic complex of the Ruppert and Hobbs coasts correlates with the Swanson
Formation exposed on the Saunders Coast. If this regional correlation is valid, the following sequence of events can be inferred for the
Ruppert and Hobbs coasts:
1. The sediments which now constitute the Wilkins Nunatak
Group were deposited unconformably upon the amphibolite 45
gneiss of the Mount Prince Group during the late
Precambrian and early Paleozoic.
2. During the Ordovician the entire area became emergent. A
regional unconformity truncated the uppermost units
within the Wilkins Nunatak Group.
3. By the end of the Paleozoic, thick geosynclinal sediments
of the Mount Pearson Group were deposited on continental
sediments of the Wilkins Nunatak Group. The Mount
Pearson Group was derived from source areas west of the
Ruppert Coast. Following deposition of the Mount Pearson
Group, metamorphism of the lower portion of the Wilkins
Nunatak Group took place.
4. Granite plutons intruded the entire lithic sequence
during the Cretaceous.
5. Block faulting occurred during the early Tertiary.
Eocene to Recent alkali-basalt complexes intruded the
southern portion of the Hobbs Coast.
6. Modem glaciation began in the Oligocene. REFERB^CES CITED
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"*"***~^~*"~^—..» PLATE II 126°
74°
A42° EXPLANATION: Cenozoic n Volcanic Rocks
Cretaceous Granitic Rocks
Metavolcanic Rocks rD (Graywackes) 75° Cretaceous or -H Schistose Rocks
75° Older D Q"artzit e
Pre- Meta-lgneous Rocks Cretaceous Structural Trend
30 60
Modified from Wade and Wilbanks 1972 Km
GEOLOGIC MAP OF RUPPERT AND HOBBS COASTS 130° PLATE Ma 134° 126' 138 74°
AA2° EXPLANATION: Mathewson Pt. 7A- N / Cenozoic F 1 Volcanic Rocks
.^-^ Cretaceous Granitic Rocks GETZ ICE SHELF N^^^ )0 Bowyer Metavolcanic Rocks (Graywackes) ) (^ Butte 75° Cretaceous or —\ Schistose Rocks '>~^Mt.Gray Peacock HOBBS COAST 75° ^- FLOOD RANGE A-A' See plate IX 30 60 Modified from Wade and Wilbanks 1972 K n INDEX TO LOCATION OF PLATES PLATE III GEOGRAPHIC PROVINCES OF ANTARCTICA EXPLANATION: I I Lithic Graywacke Tremol i te- epidote - • wollastonite schist I I Granitic Rocks \^ Trend* Flung of Fold Axij N^ Strike & Dip of Foliation X, Strike & Dip of Joint GEOLOGIC MAP OF MOUNT PEARSON 600-'Contour in Meters AND MOUNT HARTKOPF Mount Hartkopf Km Milan Rock Modified from USGS Antarctic Reconnaissance Maps PLATE IVa DEFORMATION OF BEDDING BY SHEAR MODIFIED FROM HOBBS, MEANS, AND WILLIAMS, 1976 PLATE V bai/ey Nunatak ^V EXPLANATION [_J Lithic Graywacke I [ Protoquartzite [ [ Arkose Conglomerate Partridge I I Granitic Rocks Nunatak ^ Meta-igneous Rocks N^ Structural Trend ^ V^Trend & Plunge of Fold Axes N^ Strike & Dip of Foliation ^ Strike & Dip of Foliation With Lineation 140°00' 0 1 2 "^Strike & Dip of Joint -76°00' Km /^/ Observed and Inferred Contact — 600~Contour in Meters Modified from USGS Antarctic Reconnaissance f*/laps GEOLOGIC MAP OF BAILEY NUNATAK AND WILKINS NUNATAK m^ 0 1 2 Km PLATE VI EXPLANATION: B Granitic ReDck s • Feldspathic Gra ywacke of Foliat ion \ Strike and Dip — 600-Contours in Meters Modified from USGS Antarctic Reconaissance Maps GEOLOGIC MAP OF NICKOLS ROCK PLATE Vll GEOLOGIC MAP OF MOUNT PRINCE AND PEACOCK PEAK Putzke Peak PLATE VIII EXPLANATION: I I Quartz-biotite-muscovite Schist ^ Volcanic Rocks N^ strike and Dip of Foliation Peter Nunatak ^ strike and Dip of Joint Wallace Rock N^ Trend and Plunge of Fold Axis /^ Geologic Contact ^OOO-Contour in Meters 128°00' Modified from USGS Reconaissance Maps - 76°00' GEOLOGIC MAP OF NAVARRETTE PEAK PLATE I ATLANTIC NDIAN OCEAN OCEAN 90°W Ttiurston Isia Bakutis Coasi- STUDY AREA PACIFIC 180°S OCEAN 0 500 1000 Modified from Wade and Wilbanks 1972 Km MAP OF ANTARCTICA SHOWING STUDY AREA PLATE IX POSSIBLE INTERPRETATION OF STRATIGRAPHY- RUPPEPT AND HOBBS COASTS MARIE BYRD LAND, ANTARCTICA Z CO ^ 3 Q: o o < ^ ~ p ID EXPLANATION = MOUNT PEARSON GROUP FELDSPATHIC GRAYWACKES, LITHIC GRAYWACKES AND ARGILLITE EXPOSED AT MOUNT PEARSON AND BAILEY NUNATAK UNCONFORMITY WILKINS NUNATAK GROUP 1. FELDSPATHIC, LITHIC AND SUBGRAYWACKES, PROTOQUARTZITES AND ARKOSIC CONGLOMERATES EXPOSED AT WILKINS NUNATAK 2. INTERBEDDED SANDSTONE AND SHALE EXPOSED AT NAVARRETTE PEAK AND WALLACE ROCK 3.INTERBEDDED LIMESTONE AND DOLOSTONE EXPOSED NEAR MOUNT HARTKOPF 4. INTERBEDDED LIMESTONE, DOLOSTONE, SANDSTONE, AND SHALE EXPOSED AT PEACOCK PEAK UNCONFORMITY "MOUNT PRINCE GROUP"—AMPHIBOLITE GNEISS EXPOSED AT MOUNT PRINCE AND BENNETT BLUFF A-A SEE PLATE llQ