Crustal structure and uplift mechanisms for the Transantarctic Mountains

The Transantarctic Mountains (TAM) form the uplifted flank of the West Antarctic Rift System (WARS). Although the TAM are relatively well exposed there is still much debate concerning their formation. In order to gain an improved understanding of TAM architecture and uplift mechanisms it is essential to further constrain their crustal and lithospheric structure. A number of different models have previously been put forward to explain TAM uplift, including asymmetric rifting, flexure of the East Antarctic lithosphere, erosional denudation and more recently plateau collapse. Here we present new models of crustal structure for the Prince Albert Block of the TAM, based on combined airborne gravity, land-gravity and ice penetrating radar. Our gravity models are also compared with independent wide-angle and passive seismic data onshore, and with seismic reflection profiles across the adjacent offshore rift structures. The gravity models reveal root-like thickening of the crust under the TAM, from values ~20 km under the mountain front, to 40±2 km towards the hinterland of the range and 33±2 km beneath the Wilkes Subglacial Basin (WSB). This is at odds with some previous flexural models predicting 45 km thick crust under the hinterland of the TAM and WSB. A low-density body is revealed at the base of the crust by both gravity and wide-angle seismic data, which we interpret as related to magmatic underplating. Flexural uplift models are used to estimate the amount of uplift induced by magmatic underplating, by mechanical unloading along the TAM front, and by erosion processes. In addition, we use seismic tomography data to investigate lithospheric structure and to assess the impact of hot upper mantle under the WARS on TAM uplift. Our uplift modelling results are also compared with apatite-fission track studies and with geological evidence from the Cape Roberts Drilling Project.