| Summary: | POLISH GEOLOGICAL INVESTIGATIONS IN WEST ANTARCTICA (1977-1978) Summary The geological field work was carried out by the present author at Admiralty Bay, King George Island (South Shetland Islands, West Antarctica - Fig. l) in connection with the scientific programme for 1977-1978 of the Polish H. Arctowski Station. An area of about 100 square kms between Ezcurra Inlet and Bransfield Strait, and at Point Hennequin, was mapped to l:50,000 scale (Fig. 2). The rocks investigated included mainly the Tertiary volcanic-sedimentary complex and its Mesozoic substratum (Fig. 3). The stratiform Tertiary complex (Eocene-Miocene), over 2,500 m thick, has been subdivided into a dozen or so lithostratigraphic formations, and those included in five lithostratigraphic groups. In some formations, lower units of member rank were also distinguished (Fig. 4). The complex was formed above sea level in an intramontane rift between two Andean (late Mesozoic-early Cenozoic) orogenic arcs, parts of the Antarctandes: the outer South Shetland Arc and the inner Graham Land (Antarctic Peninsula) Arc. The persistence of volcanic activity throughout most of the Tertiary indicates a tensional character of the rift, possibly as the result of up-doming of the inter-arc area, caused by subduction of the Pacific plate under the Antarctandes. The Tertiary lavas are predominantly andesitic, with basaltic (tholeiitic) varieties. A large portion of these represent extensive sheet lava flows, possibly related to long, open fissures in the centre of the rift; the centre itself could have been situated to the south of the South Shetland arc, in Bransfield Strait. Tuffs, flow breccias and agglomerates (often very coarse) are common within stratiform lava complex. Volcanic centres and stratocones directly related to the stratiform complex (i.e. as its feeders) are very uncommon in the studied area. Fresh-water basin and river deposits (tuffite, tuffitic, sandstone, conglomerate, clay, shale) are uncommon and do not exceed 10% of the total volume of the ...
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