Geology of West Worcester Hills, Southern Victoria Land, Antarctica

Richardson, Charles Doc.

West Worcester Hills is the name given for a seven-kilometre outcrop on the northeast side of the Mulock Glacier, southern Victoria Land, Antarctica. The metasediment basement rocks of this section of the Transantarctic Mountains are predominantly calcareous and calcsilicate rocks correlated with the Anthill Marble, which is part of the Skelton Group of inferred Neoproterozoic, early Cambrian age. Similar marbles occur across the Worcester Range striking northeastwards to the Skelton Glacier. Calcite-dolomite geothermometry shows that the unit was metamorphosed between 470·c to 550"C, corresponding to mid to upper greenschist facies. Closure of the paleo-Pacific ocean during the CambrianOrdovician caused subduction of ocean lithosphere under the East Antarctic craton, leading to the emplacement of the Harvey Pluton during the Ross Orogeny. This non-foliated, calc-alkalic, Cordilleran I-type granite is the first subduction related granitoid occurrence south of the W alcott Glacier. It marks the southern limit of the Koettlitz Glacier Alkaline Province, an extensional regime devoid of Cordilleran-type magmatism. U-Pb isotope dating of the Harvey Pluton gives an emplacement age of 530 ± 8Ma, approximately 30 Ma earlier than similar calc-alkaline magmatism in the Dry Valleys area to the north. The Kehle Pluton is a medium-grained, homogeneous, granodiorite with high Sr and depleted Y signifying its adakitic characteristic. The pluton is similar to other nonfoliated adakites in the Carlyon Glacier and Dry Valleys regions. Late-stage quartz-rich aphanitic dykes crosscut the pluton. Three sills and multiple dykes of Jurassic Ferrar Dolerite intrude the basement lithologies along with the Beacon Sandstone, these intrusions were emplaced in a failed rift between East and West Antarctica during the initial break-up of Gondwana. Emplacement of the sills occurred within a temperature range of 12oo·c to 1000·c. Within the basement sill several samples have been altered under greenschist to lower amphibolite facies conditions, due to the mobilisation of water from the underlying Anthill Marble. The extreme enrichment in compatible elements and depletion in REE of these chlorite-actinolite rocks relative to the host dolerite suggests that the altered dolerite represents an early cumulate fraction.

1 v. (various pagings) : col. ill., maps ; 30 cm.

2003Richardson

Abstract Only

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