Bransfield Basin, Antarctic Peninsula: Not a normal backarc basin

The Bransfield Basin, a marginal basin Located northwest of the Antarctic P eninsula, has been habitually considered as a backarc basin associated with the rollback process that took place along an inactive plate boundary, the South Shetland Trench, where the Antarctic and the Phoenix plates meet. Ne w geophysical and structural data discussed in this paper show that the bas in opening is related to a sinistral simple-shear couple between the Scotia and the Antarctic plates, and not to the previously suggested rollback mec hanism. The widening of the Bransfield Basin and the lack of trench retreat are causing compression in the South Shetland Islands. Two different neote ctonic stress directions, with interchanged stress awes, are found in the a rea of the South Shetland block.