Bransfield Strait Development In The Tectonic Framework Of Ne Antarctic Peninsula

Bransfield Strait is an incipient oceanic back-arc<br>basin developed between the South Shetland Block<br>and the Antarctic Peninsula. The combined analysis<br>of multichannel seismic profiles acquired during<br>several oceanographic cruises and the satellite free air<br>gravity anomaly map allow to establish the development<br>of this basin. The structures show an alongstrike<br>evolution and they are heterochronous. The<br>occurrence of an axial volcanism and the presence of<br>a break-up unconformity reveal that the Central<br>Bransfield Basin is an incipient oceanic basin. Continental<br>extension was asymmetrical and developed a<br>typical lower-plate passive margin in the Antarctic<br>Peninsula and a starved upper plate margin along the<br>South Shetland Block. This structure evolved from a<br>low angle normal fault initiated in the continental<br>margin of the Antarctic Peninsula with top-to-the-<br>NW displacement. The hanging wall of this fault is<br>the South Shetland Block, which moved northwestward<br>from the Antarctic Peninsula margin. Thinning<br>of the continental crust is also presently active in the<br>Western and Eastern Bransfield basins, with formation<br>of half-grabens and associate wedge structures<br>generally opening northwestward. The initiation of<br>Bransfield Strait and its present activity is as a combined<br>consequence of the end of spreading in the<br>Phoenix-Antarctic ridge (3.3