Geology of the Olympus Range Area, Southern Victoria Land, Antarctica. Scale 1:50 000 (Flat map only)

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Isaac, M.J.; Chinn, T.J.; Edbrooke, S.W.; Forsyth, P.J. 1996 Geology of the Olympus Range Area, Southern Victoria Land, Antarctica. Scale 1:50 000 (flat map). Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences geological map 20 60 p. + 1 fold. map

Abstract: The Olympus Range geological map covers an area of about 2050 sq. km in southern Victoria Land, between the Mackay Glacier in the north and the Taylor Glacier to the south. It includes the Willett Range, the Insel Range, the western parts of the Asgard, Olympus and Clare Ranges, the Barwick and Balham valleys, and parts of the Victoria, McKelvey and Wright valleys. West of the crest of the Transantarctic Mountains, only outlying nunataks project through the ice of the Polar Plateau; to the east are the almost ice-free ranges and valleys of the Dry Valleys region. Precambrian to Ordovician plutonic and metamorphic rocks are exposed in the walls of the dry valleys in the east of the map area; the oldest rocks are structurally complex Koettlitz Group schist, gneiss, amphibolite and marble (Hobbs Formation and Salmon Marble). The oldest units of the Granite Harbour Intrusives are hornblende-biotite, biotite and rare clinopyroxene orthogneisses, which intrude and were deformed and metamorphosed with the Koettlitz Group. Younger plutons of the Granite Harbour Intrusives intrude the orthogneisses and Koettlitz Group. They include the Bonney Pluton, of granodiorite to quartz diorite composition. A coarse-grained, equigranular, hornblende-biotite granite of the Wright Valley, here named the South Fork Pluton, is the youngest of the Granite Harbour Intrusives in this area, and may be a correlative of the Pearse Pluton, which crops out south of the Asgard Range. The basement rocks are truncated by the Kukri Erosion Surface and overlain by Devonian to Triassic Beacon Supergroup sedimentary rocks (Taylor Group and Victoria Group). The youngest strata crop out at the crest of the Transantarctic Mountains and in the outlying nunataks. All seven currently recognised formations of the Taylor Group are present within the map area. Windy Gully Sandstone and Terra Cotta Siltstone are present only in the southeast, and lap on to basement to the west and north. Near the head of the Balham Valley, the overlying New Mountain Sandstone is also absent, and Koettlitz Group basement is directly overlain by Altar Mountain Formation. Further north the Altar Mountain Formation is absent at least locally; north of Mount Leland basement is overlain by Arena Sandstone. The Beacon Heights Orthoquartzite forms spectacular cliffs throughout the map area; the overlying Aztec Siltstone is only present south of Shapeless Mountain. Taylor Group strata are truncated by the Maya Erosion Surface, which is overlain by formations of the Victoria Group. All four currently recognised formations of the group have been mapped, though the basal Metschel Tillite is laterally discontinuous. The Pyramid Erosion Surface separates the Metschel Tillite from the overlying Weller Coal Measures, which are well exposed in the west at Mount Fleming, in the Willett Range, and at the nunatak of Robison Peak, where there are thick, laterally persistent coal seams. The overlying Feather Conglomerate and Lashly Formation crop out extensively in the west. Koettlitz Group rocks and Beacon Supergroup strata are intruded by sills of Ferrar Dolerite up to hundreds of metres thick. Three major sills intrude at consistent stratigraphic levels - the basement sill, the peneplain sill and the Asgard sill. At Apocalypse Peaks sills amalgamate, and dolerite is present over a topographic range of 950-2250 m. Thinner and typically more variable sills intrude the stratigraphically higher Beacon Supergroup strata. Mawson Formation explosion breccia, diamictite and minor basalt overlie and intrude Beacon Supergroup strata and Ferrar Dolerite at Shapeless Mountain, Mistake Peak and Mount Dearborn. The area of the Olympus Range map is thought to be part of a single structural block, in which Beacon and Ferrar supergroup strata dip wet at 1 degree to 4 degrees. No major faults have been identified, but many stratigraphic units are offset by differential sill lift - for example, the base of the Beacon Heights Orthoquartzite is offset by 750 m over the 4 km between the Barwick Valley and Parker Mesa. Some Ferrar Dolerite sills and dikes may have exploited pre-existing faults. Valley floors are blanketed with late Cenozoic glacial, fluvioglacial and periglacial deposits. The glacial deposits include tills deposited by the East Antarctic Ice Sheet (Sirius Formation, Sessrumnir Till, Inland Forts Till, Insel Drift and minor recent tills), tills of local and cirque glaciers (including the Vida Drift and Packard Drift) and tills of ice sheet outlet glaciers (Asgard Till, Jotunheim Till, Peleus Till and Bull Drift). Colluvial deposits (including Koenig Colluvium and more recent screes), supraglacial debris, lake beds and alluvial deposits are described, together with rock weathering and permafrost features. (auths)

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