Peering Beneath the Transantarctic Mountains Rift Flank with New Gravity Data

The West Antarctic Rift System (WARS) is one of the largest and most poorly understood continental rift systems. It is flanked by the Transantarctic Mountains (TAM), which extend for over 3,000 km from the Ross Sea Rift (RSR) to the Weddell Sea. Compared to other rift flanks the range is significantly higher, longer and wider. Unravelling the tectonic, climate and ice sheet processes, which may be responsible for these unique characteristics, requires an improved knowledge of its deeper crustal architecture and uplift mechanisms. Limited wide-angle and passive seismic data have provided some insight into the boundary between East and West Antarctica, but uplift mechanisms for the TAM remain controversial. TAM uplift has been linked to Cretaceous distributed extension in the WARS, Cenozoic flexure along its flank, and erosional denudation related to glacial incision at the margin of the East Antarctic Ice Sheet, or pre-glacial fluvial incision. The most recent hypothesis is that the TAM form the edge of an elevated plateau, which collapsed in response to distributed Cretaceous extension in the WARS. Here we present new models for the crustal structure and uplift mechanisms for the TAM, based on a compilation of aerogravity and land gravity data over the Prince Albert Block (PAB) and marine gravity in the RSR. We incorporated independent wide-angle and passive seismic constraints onshore and existing seismic reflection interpretations across the Victoria Land Basin within the RSR. Our preferred model indicates that the crust beneath the PAB is 40±2 km thick. A 5 Km-thick root is imaged, in good agreement with previous interpretations further south over the TAM. We propose that a significant component of the root (ca. 3 km) is due to magmatic underplating. Flexural models show that magmatic underplating could drive up to 1/3 of TAM uplift. The remainder is modelled as a function of mechanical unloading, erosion, and thermal buoyancy.