Provenance of some glacial deposits in the Transantarctic Mountains based on Rb/1bSr dating of feldspars

Abstract

Till deposits of Cenozoic age, formerly referred to the Sirius Formation, occur in the Transantarctic Mountains at numerous scattered localities. Many of the known occurrences are at high elevations and were deposited on old erosion surfaces that pre-date the dissection of the present Transantarctic Mountains. The most extensive deposits have been found along the walls of valleys presently occupied by outlet glaciers that flow from the East Antarctic ice sheet to the Ross Ice Shelf. The origin of these tills is the subject of conflicting hypotheses. The most plausible alternatives include deposition by local mountain glaciers and ice caps and/or by ancestral outlet glaciers that drained the East Antarctic ice sheet in Cenozoic time while uplift of the Transantarctic Mountains was taking place. Size fractions of feldspar in till of possible Cenozoic age in the valleys of the Byrd and Hatherton glaciers and on the summit plateau of Table Mountain have been analyzed for dating by the Rb/1bSr method. The results are interpretable in terms of a model based on two-component mixtures of feldspar grains of differing ages. One component is derived from the igneous rocks of the local basement complex that crystallized ∼ 500 Ma ago. The other component is Precambrian in age and may have originated from the East Antarctic shield. The results indicate that till in the valleys of the Byrd and Hatherton glaciers contain a component of Precambrian feldspar and were probably deposited by outlet glaciers draining the ice sheet of East Antarctica. The till on Table Mountain (elevation 1700 m) does not contain Precambrian feldspar and was probably deposited by a local ice cap. Till of Quaternary-Recent age along the Byrd Glacier and in the coastal moraine of the Brown Hills has a local provenance.