Transantarctic Mountains Uplift revisited with Gravity data and Flexural modelling

The Transantarctic Mountains (TAM) are often regarded as the uplifted flank of the West Antarctic Rift System (WARS). The TAM are, however, higher, longer and wider compared to other rift flanks. Unravelling the processes responsible for these unique characteristics, requires an improved knowledge of the deeper crustal architecture and uplift mechanisms of the TAM. Limited wide-angle and passive seismic data have provided important insights into the boundary between East and West Antarctica, but TAM uplift mechanisms have remained both controversial and poorly constrained. We present new models for the crustal structure and uplift mechanisms over the Victoria Land part of the TAM, based on a new compilation of gravity data, including data from the adjacent Ross Sea Rift (RSR) and Wilkes Subglacial Basin (WSB). To reduce inherent ambiguities associated with gravity modelling, we also incorporated independent wide-angle and passive seismic constraints onshore, and existing seismic reflection interpretations within the RSR. Our preferred model indicates that the crust under the TAM is 40±2 km thick, while the crust under the WSB is 33±3 km thick. A ca 5-7 km-thick root is imaged under the TAM. We propose that the root may be inherited from Ross-age orogenic events that thickened the crust. The high apparent density of the root implies a reduced buoyancy, such as inferred over several old mountain belts, including the Urals, the Caledonides of eastern Greenland, and older Proterozoic orogens. Additional thickening of the dense root may reflect later underplating processes, either linked to Jurassic magmatism, or alternatively to Cretaceous-Cenozoic rifting. Our flexural models demonstrate, however, that root preservation and magmatic underplating alone cannot explain all the TAM elevation. We show that 2/3 of the elevation arise from the combined effect of mechanical unloading along the TAM rift flank, erosion, and thermal uplift due to warmer upper mantle underlying the WARS. Preliminary 3D flexural modelling suggest that although these mechanisms may broadly explain the TAM, significant differences in rift structure, inheritance, mantle flow and erosion histories need to be taken into account to explain the observed segmentation of the range.