Late Precambrian and early Paleozoic tectonism and associated sedimentation in northern Victoria Land, Antarctica

Abstract

Northern Victoria Land, part of the Trans-antarctic Mountains, occupies a key position in the reconstructed Pacific margin of Gondwana, lying near the Oligocene rift between Antarctica, Tasmania, and Australia. Sedimentology, sedimentary petrology, and structural history of the Robertson Bay Group and the Bowers Supergroup are here used to develop a regional interpretation of these rocks in plate-tectonic terms. The Robertson Bay Group, a distal shale-turbidite sequence, is interpreted to have originated in a continent-continent collision environment and was com-pressionally deformed after the Cambrian-Ordovician boundary but before Devonian time. The Sledgers Group of the Bowers Supergroup, a proximal shale-turbidite and volcanic sequence, was derived from an undissected arc environment and was deformed during the same time interval as was the Robertson Bay Group and possibly also during the Silurian-Devonian. The Cambrian Mariner and overlying Leap Year Groups represent shallow-marine and terrestrial deposition. Reworking and selective removal of unstable clasts obscure provenance, but, although these units may be derived from dissected arc sources, they are quartz-rich. They appear to have been deformed by Silurian-Devonian tectonism. The Robertson Bay Group and the Bowers Supergroup occur in large, fault-bounded terranes. The plate-tectonic interpretations developed for these units in this paper place the arc-related Bowers Supergroup between the Antarctic craton to the west and the recycled orogen-related Robertson Bay Group to the east. This geometry is not readily related to in situ tectonic environments; therefore, it is concluded that the possibility exists that these terranes are “suspect,” that is, they may be entirely allochthonous to the Antarctic craton and have been added by later accretion.