Unveiling the Antarctic basement by sampling ice field moraines (FOD39)

A thick layer of ice currently hides from view and samples about 98% of the basement lithologies that compose the Antarctic continent. Only a few outcrops are exposed and, albeit intensively studied, only provide a scarce and disparate window into the Antarctic geological history. Understanding this history is however of primary importance to address not only fundamental problems of modern geosciences (such as the mechanisms of continental crust formation, the complementary depletion of the mantle and their evolution in the early Earth), but also more local aspects such as the geological processes that contributed to build the Antarctic continent. In this project, we propose to sample the circular moraines encountered during previous expeditions in the Nansen Blue Ice Field. In blue ice fields, the ice movement has a vertical component because of obstacles blocking the gravity-driven flow. As such, blue ice fields of Antarctica have yielded more than 40,000 meteorites to date, all concentrated by this specific movement. During previous Belgian-Japanese expeditions, several unexpected moraine fields, which most likely sampled the underlying rock formation, have been observed within the Nansen Blue Ice. Even though brought-up blocks and boulders that constitute the bulk of these moraines are no longer in place, they represent the only basement samples retrievable from this section of the Antarctic continent (Sør Rondane area). Among these moraine samples, several types of sedimentary, metamorphic, acidic and basaltic igneous rocks have been observed so far. After a preliminary petrological examination of the samples recovered from these moraines, the DIABASE project will study the zircons recovered from these moraine lithologies. We plan to perform detailed and extensive U-Pb dating using the SHRIMP instrument at the NIPR partner institute, as commonly done for detrital zircons, complemented by O isotopes as well as Hf isotopic analyses using LA-MC-ICP-MS. This highly novel approach of moraine sampling will provide new insights on the hidden deep basement of the Sør Rondane area of East Antarctica, possibly unveiling peaks in the geological activity of the Southern continent, and shedding light on tectonic processes not detectable in the few available outcrops within the area.

Keywords:Antactica, Sub-Ice Geology, Geochronology, Zircon ages, Tectonics

Disciplines:Other earth sciences not elsewhere classified