Contrasting exhumation and deformation style along a rift shoulder: insights from the Transantarctic Mountains

The Transantarctic Mountains (TAM) are one of the most enigmatic topographic feature around the world growth in response to the extensional tectonics only. The TAM mark the boundary between the East Antarctic craton and the thinned crust of the West Antarctic Rift System one of the largest continental rift domain on Earth, started in the Mesozoic, and considered still active today (Storti et al., 2009; Rossetti et al., 2006). Cenozoic morphotectonic evolution and present day elevation of the TAM have been interpreted as rift shoulder uplift due to lithospheric break along the transition from thick cratonic crust and young thin crust (Van deer Beek et al., 1994). On the other hand, recent tomographic models have shown a contribution of the mantle upwelling in sustaining the present topography and controlling volcanism (Faccenna et al., 2012). Here we present a thermochronological study coupled with structural field data focused in two key areas for the investigation of the deep processes that cause the crustal deformation. The Admiralty Mountains form the northern tip of the TAM, and they are different from the rest of the chain for the extent of the uplifted area, the total amount of exhumation, and the alpine-style morphological feature. Preliminary thermochronological data of samples collected during 2014-2015 Antarctic expedition, show ages that range between 26.5±2.2 and 65.9±3.5 Ma suggesting a rapid phase around 26 Ma. The Royal Society Range is located in the South Victoria Land, near to McMurdo volcanoes. The topography is elevated up to 4000 m but characterized by a flat summit with the remnant of a paleo erosional surface. Thermochronological data suggest that the surface has been uplifted of about 1 km with respect to the adjacent region (Fitzgerald, 1992), but the total amount of exhumation and length-wave of the vertical deformation are minor with respect to the Admiralty Mts. The comparison of the exhumation pattern, faults arrangements, and volcanic evolution suggest two contrasting origins for the present topography along the rift shoulder: a mantle flow and a lithospheric flexural rebound.