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Geologic Studies in the English Coast, Eastern Ellsworth Land, Antarctica

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Geologic Studies in the English Coast, Eastern Ellsworth Land, Antarctica tains only small amounts of phillipsite, smectite, and calcite. from progressive dissolution of basaltic glass. Hydrothermal The distinct upper contact of this unit cuts across bedding. The alteration associated with dike emplacement has also produced tuffs above have been extensively altered to palagonite, palagonitization at some localities. It is probable that the altera- zeolites, smectite, and calcite. This relationship suggests that tion history of many of these deposits is complicated by the during alteration of the upper part of Castle Rock, the lower part operation of both mechanisms. was protected by ice, and authigenic mineral formation was The presence of early formed phillipsite and the persistence restricted by frozen interstitial water. With lowering of the ice of relatively fresh glass in many of the antarctic hyaloclastite level, the unaltered base was exposed to percolating meteoric samples unrelated to age, suggest that following initial pal- water. The glass, unprotected by more stable secondary miner- agonitization and authigenic mineral formation, diagenesis pro- als and palagonite, has undergone extensive dissolution. Fluc- ceeds slowly due to reduction in porosity and available exposed tuations in ice level, therefore, may affect the intensity or style glass (Fumes 1974) and to the relative lack of free water in the of postdepositional alteration. antarctic environment. Thanks to the other geologists in the field: Anne Wright, Philip Kyle, and Harry Keys (1982— 1983), David Johnson (1983 _ie "" t4!f^ - 1984), and Nelia Dunbar (1984 - 1985). This research was supported by National Science Foundation grant DPP 80-20836 to W.E. LeMasurier. References Fumes, H. 1974. Volume relations between palagonite and authigenic minerals in hyaloclastites, and its beating on the rate of palagonitiza- tion. Bulletin Volcanologique, 38, 173 - 186. Fumes, H. 1977. Element mobility during palagonitization of a sub- glacial hyaloclastite in Iceland. Chemical Geology, 22, 249 - 264. Hay, R.L., and A. lijima. 1968. Nature and origin of palagonite tuffs of the Honolulu Group on Oahu, Hawaii, Geological Society of America Memoir, 116, 338 - 376. Jakobsson, S.P. 1972. on the consolidation and palagonitization of the tephra of the Surtsey volcanic island Surtsey Progress Report, 61. 1 —8. LeMasurier, WE., and D.C. Rex. 1983. Volcanic record of Cenozoic Figure 2. Scanning electron microscope photomicrograph of phillip- glacial history in Marie Byrd Land and western Ellsworth Laid: site coating a glass fragment from Turks Head. 1 centimeter = 1 Revised chronology and evaluation of tectonic factors. In C. Crad- micrometer. dock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. The distribution and paragenesis of the alteration minerals in Staudigel, H., and S.R. Hart. 1983. Alteration of basaltic glass: Mecha- the upper, palagonitized section at Castle Rock suggest their nisms and significance for the oceanic crust-seawater budget. Geo- formation was largely controlled by increasing pH resulting chimica et Cosmochimica Acta, 47, 337 - 350. Geologic studies in the English Coast, The first visit to the previously unexplored English Coast of the Bellingshausen Sea was made during the 1984— 1985 austral eastern Ellsworth Land, Antarctica summer by a U.S. Geological Survey (UsGs) field party. Despite exceptionally poor weather, the field party completed recon naissance geologic mapping of rocks exposed in nunataks scat tered over about 16,000 square kilometers (figure 1). The fiel P.D. ROWLEY and K.S. KELLOGG party also studied rocks in the Behrendt Mountains and other nearby parts of eastern Ellsworth Land that had not beer t U.S. Geological Survey mapped before. We found that most rocks in the English Coas Denver, Colorado 80225 and adjacent parts of eastern Ellsworth Land resemble those of the southern Antarctic Peninsula (Black, Lassiter, and 0rvill W.R. VENNUM Coasts) and other parts of eastern Ellsworth Land (Laudon 1972, 1982; Williams et al. 1972; Rowley and Williams 1982; Department of Geology Rowley et al. 1983). Mesozoic igneous rocks in all these areas Sonoma State University define an Andean magmatic arc that continues northward up Rohnert Park, California 94928 the spine of the Antarctic Peninsula (figure 1). This arc de- 34 ANTARCTIC JOURNAL out in the Henry Nunataks. Based on similarity to rocks ex- Laudon, T.S., D.J. Lidke, T. Delevoryas, and C.T. Gee. 1985. Sedimen- posed broadly over West Antarctica (LeMasurier and Wade tary rocks of the English Coast, eastern Ellsworth Land, Antarctica. 1976; LeMasurier and Rex 1982), these volcanic rocks are proba- Antarctic Journal of the U.S., 20(5). bly of late Tertiary age and represent alkaline rocks erupted Laudon, T.S., M.R.A. Thomson, P.L. Williams, K.L. Milliken, P.D. during regional extensional tectonism. Rowley, andJ.M. Boyles. 1983. The Jurassic Latady Formation, south- The field party consisted of seven geologists. In addition to ern Antarctic Peninsula. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic Earth science. Canberra: Australian Academy of the authors, these included J. Michael ONeill and David J. Science. Lidke of the USGS, Denver; Thomas S. Laudon of the Univeristy LeMasurier, W.E., and D.C. Rex. 1982. Volcanic record of Cenozoic of Wisconsin at Oshkosh; and British Exchange Scientist Janet glacial history in Marie Byrd Land and western Ellsworth Land— W. Thomson of the British Antarctic Survey. The party was Revised chronology and evaluation of tectonic factors. In C. Crad- placed in the field by LC-130 Hercules aircraft of the U.S. Navys dock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Antarctic Development Squadron Six on 11 December 1984 and Press. was evacuated on 5 February 1985; time in the field was 56 days. LeMasurier, WE., and F.A. Wade. 1976. Volcanic history in Marie Byrd All of us are deeply grateful for the considerable assistance give Land—Implications with regard to southern hemisphere tectonic reconstructions. In 0. Gonzalez-Ferran (Ed.), Andean and antarctic to us by the Navy, the Division of Polar Programs, and the ITT Antarctic Services; we especially thank M.D. Turner for his volcanology problems. Rome: International Association of Volcanology and Chemistry of the Earths Interior. support. The authors thank the other members of the field party ONeill, J.M., and J.W. Thomson. 1985. Tertiary mafic volcanic and as well as Theodore Delevoryas and C. T. Gee for their help. This volcaniclastic rocks of the English Coast, Antarctica. Antarctic Journal work was partly funded by National Science Foundation grant of the U. S., 20(5). DPP 83-18183 to the USGS and grant DPP 83-19569 to the Univer- Rowley, PD., D.L. Schmidt, and P.L. Williams. 1982. Mount Poster sity of Wisconsin at Oshkosh. Formation, southern Antarctic Peninsula and eastern Ellsworth Land. Antarctic Journal of the U.S., 17(5), 38 - 39. Rowley, PD., W.R. Vennum, K.S. Kellogg, T.S. Laudon, P.E. Carrara, J.M. Boyles, and M.R.A. Thomson. 1983. Geology and plate tectonic setting of the Orville Coast and eastern Ellsworth Land, Antarctica. In R. L. Oliver, P. R. James, and J. B. Jago (Eds.), Antarctic Earth science. References Canberra: Australian Academy of Science. Rowley, PD., and P.L. Williams. 1982. Geology of the northern Lassiter Delevoryas, T., and C.T. Gee. 1985. Personal communication. Coast and southern Black Coast, Antarctic Peninsula. In C. Craddock Laudon, T.S. 1972. Stratigraphy of eastern Ellsworth Land. In R.J. Adie (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Williams, P.L., D.L. Schmidt, C.C. Plummer, and L.E. Brown. 1972. Laudon, T.S. 1982. Geochemistry of Mesozoic and Cenozoic igneous Geology of the Lassiter Coast area, Antarctic Peninsula—Preliminary rocks, eastern Ellsworth Land. In C. Craddock (Ed.), Antarctic geos- report. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: cience. Madison: University of Wisconsin Press. Universitetsforlaget. Tertiary mafic volcanic and 1970 austral summer) to the southern Antarctic Peninsula and adjacent areas. The English Coast had not been mapped pre- volcaniclastic rocks of the English viously because outcrops are few, logistical support is difficult, Coast, Antarctica and geologists wanted first to understand the geologic frame- work of the region by studying better exposed, more easily investigated mountainous terrains in adjacent areas. J.M. ONEILL Geologic mapping of the English Coast revealed that a linear chain of nunataks and mountain peaks, Snow Nunataks (see U.S. Geological Survey Rowley, Kellogg, and Vennum, Antarctic Journal, this issue), is Denver, Colorado 80225 composed of interlayered basaltic flow rocks, hyaloclastites, pillow basalts, and locally thick accumulations of volcaniclastic sedimentary deposits, probably derived in large part from the J.W. THOMSON nearby mafic volcanic centers. British Antarctic Survey Mafic volcanic rocks and hyaloclastites of West Antarctica Cambridge, CB3 OET, England form a major upper Tertiary volcanic province that extends from the Ross Sea eastward through coastal Marie Byrd Land, and the Jones Mountains in Ellsworth Land, 550 kilometers east of The English Coast, located in eastern Ellsworth Land along Snow Nunataks (LeMasurier and Wade 1976). Similar mafic the Bellingshausen Sea at the base of the Antarctic Peninsula, volcanic rocks are also exposed at scattered localities in Alex- was mapped in reconnaissance during the austral summer of ander Island (Burn and Thomson 1981; British Antarctic Survey 1984— 1985 by a team of seven geologists from the United States 1981), some 270 kilometers northeast of Snow Nunataks. Terti and United Kingdom. The expedition was the fifth in a series of ary volcanic rocks have been described also from the Merricl4 U.S. Geological Survey excursions (which began in the 1969 - Mountains (Vennum and Laudon in press), 150 kilometer ANTARCTIC JOURNA..
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