Morphostructure and recent evolution of the Bransfield Strait (NW Antartic Peninsula).

CANALS, M.; ACOSTA, J.; BARAZA, J.; BART, P.; CALAFAT, A.; CASAMOR, J. L.; DE BATIST, M.; ERCILLA, G.; FARRÁN, M.; GRACIA, E.; RAMOS, E.; SANZ, J. L.; SORRIBAS, J.; TASSONE, A

Grenoble

Simposio; EGS XIX Symposium; 1994

EGS

The Bransfield Strait is a Neogene marginal basin located between the northern tip of the Antarctic Peninsula and the South Shetland Islands. Being one of the few modem examples of a marginal basin within an ensialic arc, the basin has been explored through many different marine geophysical surveys, based mainly on magnetics, seismic reflection and refraction. Nevertheless, fundamental aspects of its structure and age are still poorly understood and controversial. During the most recent cruise GEBRA 93, carried out during December 93 aboard the BIO "Hespcrides" and in the frame of the Spanish Antarctic Program, swath bathymetric profiles (by the Simrad EM-12 multibeam echosounder), seismic reflection, BPS and magnetic profiles were made in the Central and Eastern sub-basins of the Bransfield Strait. The new detailed bathymetric map, covers an area of 17,(X)0 km2 between 49°30'W and 60°30'W and highlights the existence of abundant volcanoes. They are mainly concentrated on the SW end and NW (lank of the Central sub-basin forming two volcanic lineaments. Volcanic edifices present in the Eastern sub-basin, seem not be aligned and shifted to the SE with respect to the former. The junction between the Bransfield Strait and the SSR has also been completed following an earlier cruise (SCOTIA 92) made in February 1992. Two main families of lincations can be distinguished, one trending NW-SE (Bransfield direction), and another one trending E-W (SSR direction). Both sets of lincations determine in the westernmost part of the SSR a rhomboid-shaped depression deeper than 5000 m ("Hespcrides Deep"). We interpret this depression as a small pull-apart basin developed by the sinistral strike-slip motion along the SSR. The knowledge of the detailed seafloor morphology permits to check the validity of some of the precedent ideas on the geodynamic evolution of the Bransfield Strait area and western part of the SSR.