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.