The West Antarctic Rift System is one of the largest continental rifts on Earth. Because it is obscured by the West Antarctic Ice Sheet, its evolution is still poorly understood. Here we present the first low-temperature thermochronology data from eastern Marie Byrd Land, an area that stretches ~ 1000 km along the rift system, in order to shed light on its development. Furthermore, we petrographically analysed glacially transported detritus deposited in the marine realm, offshore Marie Byrd Land, to augment the data available from the limited terrestrial exposures. Our data provide information about the subglacial geology, and the tectonic and morphologic history of the rift system. Dominant lithologies of coastal Marie Byrd Land are igneous rocks that intruded (presumably early Paleozoic) low-grade meta-sedimentary rocks. No evidence was found for un-metamorphosed sedimentary rocks exposed beneath the ice. According to the thermochronology data, rifting occurred in two episodes. The earlier occurred between ~ 100 and 60 Ma and led to widespread tectonic denudation and block faulting over large areas of Marie Byrd Land. The later episode started during the Early Oligocene and was confined to western Pine Island Bay area. This Oligocene tectonic activity may be linked kinematically to previously described rift structures reaching into Bellingshausen Sea and beneath Pine Island Glacier, all assumed to be of Cenozoic age. However, our data provide the first direct evidence for Cenozoic tectonic activity along the rift system outside the Ross Sea area. Furthermore, we tentatively suggest that uplift of the Marie Byrd Land dome only started at ~ 20 Ma; that is, nearly 10 Ma later than previously assumed. The Marie Byrd Land dome is the only extensive part of continental West Antarctica elevated above sea level. Since the formation of a continental ice sheet requires a significant area of emergent land, our data, although only based on few samples, imply that extensive glaciation of this part of West Antarctica may have only started since the early Miocene.
Bibliographical noteFunding Information:
This study was financially supported by the German Science Foundation DFG, grant no SP 673/6-1 , in the framework of the Priority Programme SSP 1158 “Antarctic Research with comparative investigations in Arctic ice areas”. We specially thank Captain Uwe Pahl of RV Polarstern and his crew, Klaus Hammrich and Hans Heckmann from Heli Service International, Mirko Scheinert and Ralf Rosenau (TU Dresden) for their support during sampling, Anke Toltz and her team of students assistants (University of Bremen) for sample processing, and Barry Kohn (University of Melbourne) for his support regarding apatite (U-Th-Sm)/He analysis. Two anonymous reviewers are thanked for their insightful comments that helped improve an earlier version of this paper, and Sierd Cloetingh is thanked for the editorial handling.