Discovery of a Neoproterozoic basin in the Prydz belt in East Antarctica and its implications for Gondwana assembly and ultrahigh temperature metamorphism

Abstract

Detrital zircon U–Pb age data from ultrahigh-temperature metasedimentary rocks (950 °C and 10–12 kbar) in the Rauer Group and a granulite grade metasedimentary rock (850 °C and 7–8 kbar) in the Bolingen Islands in Prydz Bay, East Antarctica, indicate the existence of a Neoproterozoic (Ediacaran) cover sequence that was deposited on basement ranging in age between approximately 2800 Ma and 940 Ma. The Neoproterozoic succession has a maximum depositional age of approximately 600 Ma with derivation from igneous and metamorphic sources of Archaean, Palaeoproterozoic and Neoproterozoic age. The minimum depositional age is constrained to be approximately 575 Ma based on existing (Th + U)–Pb monazite metamorphic ages from the UHT metasedimentary rocks. The identification of Late Neoproterozoic protoliths to the UHT granulites in the Rauer Group demonstrate that ultrahigh-temperature metamorphism in Prydz Bay must be Ediacaran to Cambrian in age. The timing of basin development ( ca. 600–575 Ma) is coincident with the amalgamation of eastern Gondwana. The palaeogeography of the Prydz Bay region during the amalgamation of Gondwana is uncertain, but in our proposed reconstruction we suggest that inherited zircons were derived from Indo-Antarctic crust. Ocean closure is inferred to have occurred along a suture zone to the southeast of Prydz Bay and the Prince Charles Mountains. Our palaeogeographic model invites further work on the possibility of a shared history between India and a large portion of East Antarctica prior to the final amalgamation of eastern Gondwana during the Ediacaran–Cambrian.