Provenance of Glacially Transported Material near Nimrod Glacier, East Antarctica: Evidence of the Ice-Covered East Antarctic Shield

Abstract

Evaluation by glacial-clast petrography, igneous whole-rock geochemistry, metamorphic mineral composition, and magnetic susceptibility of glacially eroded, transported, and deposited material near Nimrod Glacier, East Antarctica provide information on the composition of the ice-covered East Antarctic shield. Precambrian basement of East Antarctica is only documented in the Transantarctic Mountains near the polar plateau of Nimrod Glacier, providing an ideal location to look for adjacent sub-ice Precambrian terrain. Over 100 igneous and metamorphic rock clasts collected from moraines near the head of Nimrod Glacier show both local and transported material. Physical characteristics of local rock fall show angular edges, whereas distantly transported material exhibits rounded edges, glacial striations, or rock types only seen upstream. Most metamorphic rock types collected show intense deformation fabrics, high-grade mineral assemblages, and high-grade P-T conditions, which are similar to the Archean and Paleoproterozic Nimrod Group. Many igneous rocks may originate from either the Nimrod Group or from the syn-tectonic and post-tectonic Cambrian-Ordovician Granite Harbour Intrusive series, and some come from nearby Ferrar dolerite (Jurassic). These samples are compared to Cambrian-Ordovician rocks in southern Victoria Land, which differ in trace element trends. Although many of the clasts can be explained by local derivation, others appear exotic and may represent more distal origins in the shield interior. Future geochronology will help to refine the relative contributions of local and distal sources to test these conclusions.