Modeling of Mineral Parageneses and Thermobarometry of Metavolcanic Rocks of the Ruker Group in the Southern Prince Charles Mountains, East Antarctica

Abstract

Diverse geological complexes that form the crystalline basement of the East Antarctic Platform crop out in the Prince Charles Mountains. The Ruker Group is a member of the metasedimentary complexes that make up the Paleoproterozoic through Neoproterozoic suprastructure of the Ruker Terrane. It is divided into two sequences consisting of highly deformed and greenschist facies metamorphosed sedimentary and volcanic rocks. The mineral and major element compositions of metavolcanic rocks have been studied and physicochemical modeling of mineral parageneses has been performed to reconstruct the P–T parameters of metamorphism. The dependence of the mineralogy of metabasic schists on the protolith composition and the ratio of components in the H2O–CO2 fluid involved in the phase reactions were analyzed. The calculated mole fraction of CO2 in the fluid equilibrated with carbonate-bearing parageneses is 0.13–0.27. It is assumed that chloritoid schist consists of metamorphosed laterites derived from basalt. Modeling and the data of chlorite–phengite thermobarometry indicate that the Ruker Group rocks were metamorphosed under conditions of the high-pressure part of the greenschist facies (300–450°C, 7–8 kb). These conditions are significantly higher than the stable continental geotherm and are close to those in the zone of a slow subduction geotherm. According to the available geological data, a similar geodynamic setting could be caused by the evolution of the Neoproterozoic intraplate sedimentary basin in connection with deep-sinking basement blocks as a result of tectonic aggregation during the closure of the basin.