UPLIFT OF THE TRANSANTARCTIC MOUNTAINS AND THE BEDROCK BENEATH THE EAST ANTARCTIC ICE-SHEET

In recent years the Transantarctic Mountains (TAM), the largest noncon tractional mountain belt in the world, have become the focus of modele rs who explained their uplift by a variety of isostatic and thermal me chanisms. A problem with these models is a lack of available data to c ompare with model predictions. We report here the results of a 312-km- long geophysical traverse conducted in 1993/1994 in the hinterland of the TAM. Using detailed subglacial topography and gravity measurements , we confirm the origin of the TAM as a flexural uplift of the edge of East Antarctica. Using an elastic model with a free edge, we can join tly fit the topography and the gravity with a plate having an elastic thickness of 85 +/- 15 km and a preuplift elevation of 700 +/- 50 m fo r East Antarctica. Using a variety of evidence, we argue that the upli ft is coincident with a relatively minor tectonic event of transtensio nal motion between East and West Antarctica during the Eocene rather t han the Late Cretaceous rifting event that created the Ross Embayment. We suggest that this transtensional motion caused the continuous plat e to break, which created an escarpment that significantly increased t he rates of erosion and exhumation. Results from the geophysical trave rse also extend our knowledge of the bedrock geology from the exposure s within the TAM to the ice covered interior. Our interpretation sugge sts that the Ferrar flood basalts extend at least 100 km westward unde r the ice. The Beacon Supergroup of Paleozoic and Mesozoic sediments t hins gradually under the ice and its reconstructed thickness is remini scent of profiles of foreland basins. Finally, there is no indication in the gravity field for an incomplete rebound due to significant melt ing of the East Antarctic ice sheet since the last glacial period.