Crustal architecture and tectonic evolution of a major pull-apart basin in East Antarctica

Strike-slip faulting can lead to pull-apart basin formation, which can provide clues into complex multi-stage rifting, including oblique extension. The Rennick Graben (RG) is an example of such pull-apart basins and is located in northern Victoria Land (NVL), East Antarctica. The RG has been interpreted as an extensive left lateral Cretaceous(?) pull-apart basin linked to the Victoria Land Basin, part of the West Antarctic Rift System (WARS). Alternatively, it has been interpreted as a more localised Cenozoic right-lateral basin unconnected to the WARS. Here we present the first results of a new project (REGGAE) that aims to re-investigate the architecture and evolution of the RG by analysing aeromagnetic, aerogravity and land-gravity and bedrock topography data together with new structural and thermochronology constraints. Maximum horizontal gradient of pseudo-gravity, tilt derivative and isostatic residual gravity maps provide tantalising new geophysical views of the RG. The north-eastern shoulder of the RG is clearly controlled by a major inherited fault, the Lanterman Fault that was active during the Ross Orogen and may have been repeatedly reactivated. The USARP Mountains are often depicted as the north-western flank of the RG, but here we hypothesise that this region was originally located within the RG, as part of an early stage of more distributed (late Cretaceous-Paleogene?) extension and inferred left-lateral strike-slip faulting. Strengthening of the lithosphere may have followed, leading to narrower more focussed extension during right-lateral strike-slip faulting. Overall, the geophysical images and the spatial distribution of Jurassic volcanics support the interpretation that the RG extends further south and is kinematically connected with both the western edge of the WARS and the eastern margin of the Wilkes Subglacial Basin. However, 3D gravity inversions demonstrate that the RG does not exhibit such thin crust or lithosphere as observed within the WARS. Aeromagnetic imaging confirms that it was also un-affected by voluminuous Cenozoic magmatism and post-Jurassic sedimentary infill is also lacking in contrast to the Ross Sea Rift basins. Major tectono-thermal segmentation is therefore apparent, as observed in many other rift and pull-apart systems affected by multistage evolution.