South Georgia in a West Gondwana context: detrital zircon geochronology of a late Permian accretionary complex

Abstract

South Georgia lies in a remote position in the circumpolar South Atlantic and forms one of the most isolated continental fragments on Earth. The basement geology of South Georgia is restricted to the southeast sector of the island and is termed the Drygalski Fjord Complex, which consists of metasedimentary rocks and localised paragneisses that form an accretionary complex cut by multiple dolerite dykes and gabbroic intrusive rocks. The basal Salomon Glacier Formation has a maximum likely depositional age of c. 270 Ma that is consistent with West Gondwana accretionary complexes from the Antarctic Peninsula and Patagonia, but also identical in depositional age to sedimentary successions from the Karoo Basin (South Africa) and East Antarctica. Any correlation to the sedimentary units from South Africa and East Antarctica can be ruled out as they lack a secondary age peak at c. 470 Ma, ubiquitous across Gondwana margin accretionary complexes, and are instead characterised by a secondary age peak at c. 530 Ma, associated with the recycled Cambrian sources of East Antarctica. The late Permian accretionary complex of South Georgia is closely correlated to units from the northern Antarctic Peninsula (Trinity Peninsula Group) and the southern Cordillera Darwin, and we favour a common origin on the Antarctic Plate before closure of the Rocas Verdes Basin and translation to the Scotia Plate.