Provenance of continental blocks in the southern Scotia Sea using detrital zircon U-Pb geochronology

Reconstructions of the opening of the Scotia Sea and the Drake Passage oceanic gateway have traditionally been based on considerations of ocean spreading and rifting between crustal blocks, and geological correlations based on sequences on islands such as South Georgia and the South Orkney Islands. Detrital zircon U-Pb geochronological data derived from dredged schists and sandstones from two submerged continental blocks in the southern Scotia Sea, Bruce Bank and Discovery Bank, provide further constraints on the origin and tectonic movement of the blocks and confirm the use of detrital geochronology for understanding the tectonic evolution of the Scotia Sea. Bruce Bank yielded greenschist facies schist with a Triassic maximum sedimentation age of 216.2 Ma, similar to schist dredged from the northern continental margin of the adjacent South Orkney microcontinent. Both schists are correlated with metamorphic rocks of an accretionary complex exposed on the South Orkney Islands. Sandstones with Permian to Triassic maximum sedimentation ages of 258–224 Ma were dredged from both the northern margin of the South Orkney microcontinent and Discovery Bank. A younger sedimentary unit with Cretaceous maximum sedimentation ages of 140–110 Ma has been recovered from both Bruce and Discovery banks. The new data are consistent with the interpretations that Bruce and Discovery banks were joined in mid-Cretaceous times and that both were proximal to the South Orkney Islands in a position on the paleo-Pacific margin of Gondwana before Late Cretaceous-Cenozoic rifting, translation of the crustal blocks, and formation of the Scotia Sea.