The age of the Weddell Basin

Abstract

The deep oceanic basin occupied by the Weddell Sea separates the East Antarctic craton from the Antarctic Peninsula, a largely post-Palaeozoic orogenic belt. An understanding of the tectonic evolution of the basin would resolve most of the remaining problems of Gondwanaland reconstruction, which revolve around the relative positions of these two fragments and South America. Norton and Sclater¹ conclude that Indian Ocean marine geophysical data essentially support the Smith and Hallam fit², but the unacceptable overlap ofundoubtedly old continental crust^3–5 on the Antarctic Peninsula and Falkland Plateau implies relative motion between the Peninsula and East Antarctica. Such motion is not required by the reconstruction of Barron and others^7,8 which, however, can be criticized on other grounds^9,10. The marine geophysical observations within the intervening ocean basins have proved useful in formulating plate tectonic reconstructions. Fracture zone trends, seafloor spreading type magnetic anomalies, crustal heat flux, and crustal depth all provide clues to the timing and direction of the continental motions. The acquisition of geophysical data from the Weddell Sea region has been slow^11–13. However, the combined interpretation of the two largest data sets extant^12,13 now being undertaken, seems likely to provide a more tightly constrained Gondwanaland solution. As a first step, we report here an estimated age for the Weddell Sea floor in the area bounded by 60° and 73° S, 5° and 35° W shown in Fig. 1.