Provenance of rifted continental crust at the nexus of East Gondwana breakup

Abstract

The Bruce Rise, a prominent bathymetric feature offshore the Bunger Hills (East Antarctica), has basement of unknown crustal affinity and age. In East Gondwana, the Bruce Rise is reconstructed near the Naturaliste Plateau (offshore SW Australia) and microcontinents now submerged in the eastern Indian Ocean. New zircon U-Pb-Hf data from two c. 1150 Ma granite samples dredged from the eastern escarpment of the Bruce Rise demonstrate that these rocks are dominated by xenocrystic cargo. Mesoproterozoic xenocrystic cores show textural evidence of melt-mediated coupled dissolution-precipitation to form rim domains with apparent ages that skew towards c. 1150 Ma. The zircon U-Pb-Hf signatures from the xenocrysts in the Bruce Rise granites, and from c. 1230 to 1180 Ma felsic-intermediate granites and orthogneisses from the conjugate Naturaliste Plateau basement, suggest late Mesoproterozoic magmatism occurred at a transition in the regional tectonic architecture between a reworked Archean cratonic margin and Proterozoic juvenile crust. On the basis of plate reconstructions, exhumation and thinning of the basement to the Bruce Rise/Naturaliste Plateau occurred predominantly during rifting of India (prior to c. 120 Ma). Minor further thinning likely occurred leading up to the onset of seafloor spreading between Australia/Naturaliste Plateau and Antarctica/Bruce Rise (from c. 90 to 84 Ma).