ALBERT

Description: The India-Antarctica separation is still an open problem due to the absence of critical geophysical data. So far no wide-angle data existed along the conjugate margins of East India and the Enderby Land off East Antarctica to define the position and composition of the continent-ocean boundary - a pre-requisite for any sound reconstruction. Furthermore, along both margins only old marine magnetic random track data are available for identifying seafloor spreading anomalies to describe the drift of both continents in the Cretaceous. The Kerguelen Plateau, located just north of the East Antarctica coast, however, has been drilled several times providing the only reliable age constraint on the formation of this huge magmatic plateau. In general, the poor information resulted a wide variety of kinematic models for the drift of the India. In the last years several newly acquired geophysical data provide new constraints on its drift. Two deep seismic sounding lines off Prydz Bay and across the Princess Elisabeth Trough show that oceanic crust is already present much closer to the present-day shelf break than previously known. Magnetic data acquired parallel to these lines provide excellent timing constraints for the initial breakup of India. Finally, marine magnetic data gathered in 2017 south of Sri Lanka indicate that here the oceanic crust is definitely younger than magnetic chron M0, questioning several kinematic models for the Indian Ocean. The latest results will be presented.

Description: The Dronning Maud Land Mountains in East Antarctica form a key area for the better understanding of the geodynamic evolution of East Antarctica. Specifically, the integration of geophysics with geology and geochronology reveals the complex tectonic history of East Antarctica and its significance for Rodinia and Gondwana reconstructions. The international GEA-expeditions (2010-12) revealed three major tectonic provinces: a westernmost part with Kalahari (Africa) affinities and an easternmost part from about 35E with Indo-Antarctic affinities sandwiched in between these two blocks, is an extensive region with juvenile Neoproterozoic crust (ca. 990-900 Ma), the Tonian Oceanic Arc Super Terrane (TOAST) that shows very limited signs of a pre-Neoproterozoic history. We have tested the spatial extent of the TOAST by a regional moraine study that confirm the lack of older material inland, though latest Mesoproterozoic juvenile rocks frequently do occur in the glacial drift and probably record a slightly earlier precursor of the TOAST inland. The TOAST records 150 Ma of almost continuous tectono-metamorphic reworking at medium- to high-grade metamorphic conditions between ca. 650 to 500 Ma. This long-lasting overprinting history is thought to record protracted accretion of ocean island arc terranes and the final amalgamation of East Antarctica along the major East African-Antarctic Orogen. There is no sign of significant metamorphic overprint immediately after the formation of TOAST. Therefore, these island arcs may have formed independent of, or peripheral to Rodinia, and may reveal major accretionary tectonics outboard of Rodinia.