Tectonic development of the Bransfield Basin and its prolongation to the South Scotia Ridge, northern Antarctic Peninsula

Abstract

The Bransfield Basin is located off the northern tip of the Antarctic Peninsula. The analysis of multichannel seismic reflection profiles allows the shallow structure of the Bransfield Basin and its eastwards prolongation through the Scotia Sea to be imaged. The Bransfield Basin is asymmetrical, with most of the sediment input coming from the passive Antarctic Peninsula margin, which is deformed by normal faults generally dipping less than 45° northwestwards. Much less sediment comes from the conjugate South Shetland Islands margin, which is dominated by high-angle normal faults, generally dipping between 45° and 60°, constituting the inner boundary of the South Shetland Block tectonic horst. The detachment and moving apart of the South Shetland Block from the Antarctic Peninsula led to the opening of the Bransfield Basin, where incipient oceanic spreading has been reported previously. The South Shetland Block outer boundary to the northwest is made of the South Shetland Trench, which to the east passes into the sinistral transpressive Scotia–Antarctic plate boundary marked by the prominent South Scotia Ridge. Following cessation of spreading in the Phoenix–Antarctic Ridge northwest of the South Shetland Block during middle Pliocene, roll-back played a major role in the development of the Bransfield Basin, with maximum extension in the Central subbasin. In addition, the Eastern Bransfield Basin accommodates most of the sinistral transtensional deformation along the South Scotia Ridge. Normal and reverse faults were simultaneously active along the inner and outer boundaries, respectively, of the continental crust fragment constituting the South Shetland Block. The development of the Bransfield Basin offers a good example of the tectonic processes involved in continental fragmentation associated with backarc basin development.