Paper No. 6
Presentation Time: 9:15 AM
PERMIAN AND TRIASSIC SANDSTONES IN THE CENTRAL TRANSANTARCTIC MOUNTAINS AND WEST ANTARCTICA REFLECT THE CONTEMPORANEOUS AND EVOLVING GONDWANA MARGIN
ELLIOT, David, Byrd Polar Research Center and School of Earth Sciences, The Ohio State University, Columbus, OH 43210, FANNING, C. Mark, Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia, HULETT, S.R.W., School of Earth Sciences and Byrd Polar Research Center, The Ohio State University, Columbus, OH 43210, ISBELL, John L., Geosciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53201 and LAUDON, Thomas, Department of Geology, University of Wisconsin-Oshkosh, Oshkosh, WI 54901, elliot.1@osu.edu
The Permo-Triassic sedimentary basin in the central Transantarctic Mountains evolved from a rift to a foreland basin in response to Gondwana plate margin processes. Sandstones from the lower part of the Permian section on the active margin flank of the basin, and derived in part from West Antarctica, suggest a source terrain in which zircons of Neoproterozoic to Cambrian (Ross Orogen) age were dominant, and with a trace component of ca 1.0 Ga Grenville-age grains. In mid to late Permian time (upper Buckley Fm) there was an abrupt influx of volcaniclastic detritus with zircons of contemporaneous and older Permian age. Pre-Permian zircon populations indicate continued erosion of Ross-age grains from a West Antarctic source. Zircons from eastern Ellsworth Land are mainly of late Permian age, but with a significant Carboniferous component. For the overlying Triassic Fremouw Fm sandstones, paleocurrent data show derivation from West Antarctica. Zircons in quartzose sandstone in basal Fremouw beds are dominated by Ross-age grains, but include Permian and Carboniferous clusters that are consistent with plate margin derivation. Higher in the Fremouw there are significant Triassic components along with older Carboniferous, Devonian and Ross-age grains. In the overlying Falla Fm in the axial part of the basin with longitudinal flow, zircons of late Triassic age are present.
Granitoids and orthogneisses along the Gondwana margin indicate activity at least intermittently from late Carboniferous through Triassic time. Late Carboniferous detrital zircons and zircons spanning all the Permian in upper Buckley beds are consistent with the Gondwana margin magmatic arc. The absence of Permian zircons in pre-upper Buckley strata suggests that prior to that time zircons eroded from the orogen were trapped in a proximal basin but were later recycled as a result of tectonism that initiated the flood of volcanic detritus. Sources for Ross- and Grenville-age grains could be the Ordovician Swanson Fm and its inferred subglacial extension, or Devonian strata uplifted along the inferred Gondwanide fold and thrust belt, or the presence of Ross Orogen and Grenville-age basement rocks in West Antarctica. Zircons in Triassic beds indicate more varied sources in West Antarctica, and magmatism that continued into late Triassic time.
