Palaeoproterozoic granulite-facies metamorphism in the eastern Alxa Block: New petrological and geochronological evidence from the Diebusige Complex

Abstract

The Diebusige Complex, the highest-grade metamorphic complex in the Alxa Block, can provide significant insights into the origin, formation, evolution, and tectonic affinity of the Alxa Block. Petrographic observations show that the mineral assemblage of (garnet) magnetite quartzite from the Diebusige Complex is magnetite + quartz + hypersthene + plagioclase ± clinopyroxene ± garnet. The metamorphic temperature (T) is constrained to 800–860 °C by the two-pyroxene geothermometer, corresponding to granulite-facies metamorphism. Geochronological studies involving cathodoluminescence (CL) images, LA-ICP-MS U-Pb dating, and trace element analyses of zircons show that the time of granulite-facies metamorphism was approximately 1850 Ma. Combined with the corresponding published data, this paper suggests that the metamorphic basement rocks of the Alxa Block record Neoarchaean-early Palaeoproterozoic magmatic-metamorphic and late Palaeoproterozoic granulite-facies metamorphic events, thereby indicating the affinity between the Alxa Block and the Khondalite Belt (KB).