Relics of a complex triple junction in the Weddell Sea embayment, Antarctica

Interpretation of an airborne magnetic data compilation containing a key, new survey, together with re-tracked satellite gravity data from the Weddell Sea embayment (WSE), West Antarctica, suggests Rift-Rift-Rift triple junction formation at the onset of Gondwana breakup in the Early Middle Jurassic. A complex system of northwest-southeast rifts was active contemporaneously with an east-west trending rift. This rift activity led to northward separation of the Falkland Plateau, and formation of the Weddell Sea by sea floor spreading. Atypically, the Jurassic passive margin of Gondwana shows evidence for coeval extension in two directions and a large volume of interpreted magmatic material. This is consistent with initial doming above a mantle plume and we suggest that this resulted in the formation of a triple junction. Magnetic anomalies indicate a series of faults perpendicular to igneous intrusions and extrusions with outlines that range in shape from lozenges to parallel ridges. They show remarkably good spatial correlation with free air gravity anomalies, even in areas of sea ice. We base a structural elements map and timing sequence for the events in the WSE during early Gondwana breakup on anomaly cross-cutting relationships. (C) 2000 Elsevier Science B.V. All rights reserved.