NEODYMIUM ISOTOPE STUDIES OF PROVENANCE OF GLACIAL TILLS IN ROSS SEA, AND VICINITY, ANTARCTICA

The Nd isotopic compositions of 20 samples of glacial tills from East and West Antarctica were measured to determine the provenance of till on the Ross Sea continental shelf. Fundamental differences in rock types and ages beneath source areas should allow the provenance of tills across the Ross Sea to be determined, facilitating the reconstruction of Late Pleistocene ice flow paths. We hypothesize that till obtained from beneath the West Antarctic ice sheet and till collected from the margins of outlet glaciers draining the East Antarctic ice sheet will be isotopically distinct.

Overall, measured eNd values vary from –3.8 to –14.3, while Nd model ages range from 0.8 Ga to 1.7 Ga. The till with the lowest eNd (-15) values is from the Mt. Achernar area adjacent to the Beardmore Glacier, consistent with its derivation from the erosion of reworked Archean rocks present in the central Transantarctic Mountains (Borg et al., JGR, 95, 1990). Further to the north, Late Pleistocene till at the western margin of the Ross Sea (Drygalski Trough) have the highest measured eNd (-3.8) and were likely derived from adjacent Cenozoic volcanic rocks. Tills collected from the central Ross Sea and beneath the Ross Ice Shelf (RISP) have eNd values (-7 to -10) that lie in between these two extremes and overlap the range of isotopic compositions determined for Cambro-Ordovician granitic rocks in the Transantarctic Mountains (Borg et al., 1990). Our data suggest that the majority of the Late Pleistocene tills present in the central Ross Sea and from the RISP site represent products of erosion of East Antarctic surface rocks. None of the sediment yet analyzed shows evidence that Tertiary volcanic rocks thought to underlie a significant portion of the West Antarctic ice sheet represent a major source of glacial sediment deposited in the central Ross Sea.