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Analysis of Geologic Collections Rocks of Coastal Enderby Land Near Molodezhnaya Station, Antarctica CAMPBELL CRADDOCK Department of Geology and Geophysics P

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Analysis of Geologic Collections Rocks of Coastal Enderby Land Near Molodezhnaya Station, Antarctica CAMPBELL CRADDOCK Department of Geology and Geophysics P Eastin, R. 1970. Geochronology of the Basement Rocks of of Gondwanaland are in preparation. A paper sum- the Central Transantarctic Mountains. Unpublished marizing the significance of antarctic geology to the Ph.D. dissertation, Department of Geology, The Ohio Gondwanaland hypothesis appeared recently in this State University. journal. Neethling, D. C. 1970. Geology of the Ahlmann Ridge, western Queen Maud Land. Antarctic Map Folio Series, 12, sheet 7. Reference Roots, E. F. 1970. Geology of western Queen Maud Land. Antarctic Map Folio Series, 12, sheet 6. York, D. 1966. Least-squares fitting of a straight line. Craddock, C. 1970. Antarctic geology and Gondwanaland. Canadian Journal of Physics, 44: 1079-1086. Antarctic Journal of the U.S., V(3): 53-57. Analysis of Geologic Collections Rocks of Coastal Enderby Land Near Molodezhnaya Station, Antarctica CAMPBELL CRADDOCK Department of Geology and Geophysics P. B. MYERS, JR. and E. E. MACNAMARA University of Wisconsin, Madison Department of Geological Sciences Lehigh University Since 1959, the writer and his associates have carried out eight antarctic geologic field programs, mainly in Ellsworth Land and Marie Byrd Land. Under the auspices of the USARP exchange- This report summarizes progress during the past year scientist program, the junior author conducted pedo- toward completion and publication of the results of logical, ecological, and geological surveys in coastal this work. Enderby Land from March 1967 to March 1968 as All fossil collections are now under study by spe- a member of the XII Soviet Antarctic Expedition. cialists. Professor Gerald Webers of Macalester Col- Major studies and collections were made in the lege is working on the Paleozoic faunas from the vicinity of the U.S.S.R. research station Molodezh- Ellsworth Mountains, and Dr. James Schopf of the naya (67°40S. 45°51E.). This note describes rock U.S. Geological Survey is studying the Permian floras types of the station environs. from these mountains. Precambrian stromatolites, All the rock exposures of the area are part of the collected in the Thiel Mountains in 1959, are in the Precambrian crystalline basement of the antarctic hands of Mr. William Breed of the Museum of platform. The rocks are exposed in a series of ridges Northern Arizona. Fossils collected last year in the which strike in a WNW direction. The principal Jones Mountains—probably plants of Mesozoic age— rock types are finely to coarsely banded amphibolized are under study at the University of Michigan. pyroxene-plagioclase gneisses and biotite leucogranite Several manuscripts are presently in first draft. gneisses. Foliation in the gneisses strikes roughly Dr. Bernhard Sporli of the University of Auckland parallel to the exposed ridges and dips predominantly has completed a preliminary report on the geology of southward at steep angles to 700. Mineral assemblages the Ruppert Coast. Professor Robert Rutford of the suggest that the basement gneisses were originally University of South Dakota and the writer have elevated to granulite facies assemblages, but subse nearly finished a report on Tertiary glaciation in the quent retrogressive metamorphism has produced Jones Mountains. Mr. Craig White has completed assemblages characteristic of almandine-amphibolite the petrographic study of rocks from the Eights facies metamorphism throughout much of the area. Coast and has prepared a preliminary report on the Along the coast, in the vicinity of "Granat Point," geology of that area. for example, there is little evidence remaining of The writer has invested most of his time in prepa- original granulite facies metamorphism. rations for the 1970 antarctic geology symposium in In the granitized and amphibolized pyroxene- Oslo and in the geology folio of the American Geo- plagioclase gneisses of the basement rocks, the lighter- graphical Societys Antarctic Map Folio Series. A colored bands are composed of plagioclase, commonly review paper on antarctic tectonics is in preparation andesine averaging approximately An 3 , quartz, and for the Oslo symposium. Compilation maps of the one or all of the following colored minerals: biotite, entire continent showing 1) fossil localities, 2) radio- hornblende, and pyroxene. The most common py- metric age determination localities, and 3) bedrock roxene exhibits a light pink to light green pleochroism geology have been completed for the AGS folio, and and has all of the properties of ferrohypersthene a tectonic map of Antarctica and a reconstruction with the exception of an inclined extinction. Small, 158 ANTARCTIC JOURNAL xenoblastic grains of clinopyroxene, saute, were also mon. Emplacement appears to have been controlled observed in a few sections. Hornblende, when present, by incipient joint sets in the basement gneisses. The occurs as irregularly shaped grains possessing a char- pegmatites and aplites have essentially the same acteristic poikioblastic texture. Biotite is present in all mineral composition as the leucogranite bands in the samples. Plagioclase in the form of xenoblastic grains gneisses and are interpreted as the products of ana- makes up between 50 and 70% of the lighter bands. tectic processes accompanying migmatization of the It is commonly antiperthitic, and in many sections country rock. Aplites tend to have more plagioclase has been slightly sericitized. K-feldspar, other than and less microcline than pegmatites. The pegmatites that included in antiperthites, is either totally absent are simple and contain few minerals that are foreign or present only in small quantities. Ubiquitous ac- to the country rock. Both rock types have granoblastic cessory minerals are zircon, apatite, and ore minerals, textures. Myrmekite is a common constituent of the commonly titaniferous magnetite. Other common aplites, but is relatively rare in the pegmatites. The accessory minerals include spene, rutile, and allanite. microcline of the pegmatites is highly fractured and Muscovite was observed in only one sample and was slightly sericitized along fracture planes. definitely of secondary origin. Chlorite after biotite Along the coast in the vicinity of "Granat Point," is another secondary mineral that was observed. Two the bedrock consists of a garnetiferous, amphibolitic specimens revealed minute patches of secondary cal- biotite gneiss. Rocks at this locality contain the only cite. Minute grains of sillimanite were observed in garnet observed in the vicinity of the station and one section. The light-banded rocks possess grano- exhibit evidence of more intense deformation than blastic textures. Minor cataclasis along grain bound- the rocks in the surrounding area. Cataclasis has aries was observed in many samples, and undulatory produced thin wavey planes of ground-up material, extinction of both quartz and feldspar is common. 1-2 mm thick and separated by zones of relatively The darker-colored bands contain essentially the less cataclastized material that are approximately same mineral constituents as the light bands, but 5 mm thick. Undulatory extinction is extreme in both the percentage of colored minerals is greater. Biotite the feldspars and the quartz. Twin lamellae in the with pyroxene and/or hornblende compose between plagioclase are bent. Zones of what appears to be 40 and 70% of the total rock. The remainder of mylonite suggest that the more intense deformation the dark bands is made up of plagioclase (An 5 may be related to faulting. 40) with minor quartz and accessory apatite, zir--An Erratics from the Campbell and Hays Glaciers con, and ore minerals. Sphene is an abundant acces- indicate that similar rock types persist for some dis- sory in those bands that are rich in hornblende. tance inland. In addition to local rock types, erratics The dark bands have a more schistose texture than of charnockite, amphibolite, tremolite marble, quartz- the light bands. ites, and pyroxenites and basalts were collected. Dark lenses and pods of ultramafic materials are common in the basement gneisses. These contain no feldspar or quartz and are made up essentially of hornblende and pyroxene. Olivine and spinel are common accessory minerals. A vermiform intergrowth of spine1 and hornblende observed in one specimen has been ascribed to retrogressive metamorphism. Rubidium-Strontium Dates and Accessory ore minerals, predominantly magnetite, are Sr87/Sr86 Initial Ratios of Rocks abundant in these rock types. from Antarctica and South America: Light colored bands of biotite leucogranite are also A Progress Report common in the gneisses of the area. These rocks are composed essentially of microcline, quartz, and plagi- MARTIN HALPERN oclase, with minor amounts of biotite oriented in thin bands. Microcline and antiperthitic plagioclase Division of Geosciences (Oligoclase-Andesine) make UI) over 70% of the rock. University of Texas at Dallas The plagioclase is highly embayed by myrmekite. Zircon and apatite are common accessories in these The objective of this report is to list the results bands. of a continuing University of Texas at Dallas rubid- Late-stage dikes of pegmatite and aplite cut the ium-strontium dating program related to the crustal foliation of the basement gneisses at essentially right evolution of Antarctica in a Gondwanaland frame- angles. These are tabular bodies that range in thick- work. ness from a few centimeters up to several meters and The calculated ages are consistent with the con- have sharp, planar contacts with the country rock. cept of the past existence of a Gondwanaland (Ant- A thin (0.5-15 cm) bleached contact zone is com- arctic Journal of the U.S., 1970) which fragmented September—October 1970 159.
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