ANTARCTIC TECTONICS - CONSTRAINTS FROM AN ERS-1 SATELLITE MARINE GRAVITY-FIELD

A high-resolution gravity field of poorly charted and ice-covered ocea n near West Antarctica, from the Ross Sea east to the Weddell Sea, has been derived with the use of satellite altimetry, including ERS-1 geo detic phase, wave-form data. This gravity field reveals regional tecto nic fabric, such as gravity lineations, which are the expression of fr acture zones left by early (65 to 83 million years ago) Pacific-Antarc tic sea-floor spreading that separated the Campbell Plateau and New Ze aland continent from West Antarctica. These lineations constrain plate motion history and confirm the hypothesis that Antarctica behaved as two distinct plates, separated from each other by an extensional Belli ngshausen plate boundary active in the Amundsen Sea before about 61 mi llion years ago.