Sr and Nd Isotopic evidence in metacarbonate rocks for an extinct Island arc–ocean system in East Antarctica

摘要

Chemically precipitated carbonate sediments directly record seawater composition that helps to decode the Earth’s paleo–environment, the existence of paleo–oceans, and provide valuable clues on the paleo–tectonic position of continents through Earth’s history. In addition, the geochemical and isotopic composition of carbonate rocks have a strong dependence on the depositional tectonic setting and surrounding source rock composition. This was particularly important in the Precambrian, during which biological activity was less prominent and vegetation was virtually absent. Here we present evidence for the existence of an extinct East Antarctic Ocean and its peripheral oceanic island arc system that preceded the formation of the East Antarctic continent in the Neoproterozoic before the final assembly of Gondwana. Applying a multi–element isotope geochemical approach on chemostratigraphically well–constrained metacarbonate rocks collected from the remote S?r Rondane Mountains in East Antarctica, we present a model on carbonate deposition surrounding an island arc system, mid–ocean volcanic islands and a shallow marine continental shelf of a yet unidentified interior Antarctic continent, all of which accreted in the late Neoproterozoic to early Paleozoic to form the present day East Antarctic continent prior to the final amalgamation of Gondwana supercontinent. Our results support the presence of an oceanic island arc system that might have separated the Mozambique ocean and East Antarctic ocean.