MORPHOSTRUCTURE AND EVOLUTION OF THE CENTRAL AND EASTERN BRANSFIELD BASINS (NW ANTARCTIC PENINSULA)

The Bransfield Basin is a narrow and elongated active rift basin locat ed between the Antarctic Peninsula and the South Shetland Islands. The Bransfield Basin is composed of three small basins, and two of them, the Central and Eastern Bransfield Basins, were surveyed during a rece nt cruise (GEBRA 93). The full swath bathymetry coverage as well as th e single-channel seismic reflection and magnetic profiles that have be en acquired, help us to better understand the morphostructure and rece nt evolution of the Bransfield Basin. Six large volcanic edifices alig ned with the basin axis stick out of the sedimented seafloor of the Ce ntral Bransfield Basin. In contrast, the Eastern Bransfield Basin is c haracterised by four deep troughs displaying a rhombic-shape, and smal l, scattered volcanic cones located in the southwestern half basin. Se amount volcanism plays an important role in the formation of new crust in the Bransfield Basin. The larger seamounts of the Central Bransfie ld Basin are located al the intersection of the two main orthogonal se ts of faults (longitudinal ENE-WSW and transversal NNW-SSE). Morpholog ical analysis of the seamounts indicates a multi-staged volcano-tecton ic construction. The distribution and shape of these edifices suggests that both volcanism and extension are concentrated at the same prefer ential areas through time. This might be related to the fracturation s tyle of the continental crust. The Central and Eastern Bransfield Basi ns are very different in morphostructure, volcanism, and sedimentary c over. The Central Bransfield Basin shows evidence of NW-SE extensional faulting and focused active MORB-volcanism interpreted as result of i ncipient seafloor spreading. The Eastern Bransfield Basin is still in a rifting stage, mainly dominated by a NW-SE extension and some left-l ateral strike-slip component probably related to the South Scotia Ridg e.