Paleoproterozoic multiple magmatic-metamorphic events in the Dunhuang Block, eastern Tarim Craton: Implications for assembly of the Columbia supercontinent

Abstract

The evolution of the Dunhuang Block associated with the assembly of the Columbia supercontinent is poorly constrained. The geochemical composition and temporal evolution of magmatic and metamorphic rocks may hold key information regarding critical geodynamic processes that occurred during the evolution of the Dunhuang Block. In this paper, we present a systematic petrographic, geochemical, and zircon U-Pb and Hf isotopic investigation on tonalitic gneiss, carbonatite, granitic dyke, mafic granulite and A-type granite in the Dunhuang Block. The results suggest that tonalitic gneiss was derived from partial melting of a thickened oceanic plateau crust or island-arc crust at ~3.67 Ga and then it recorded an important subduction-collision orogenesis in the Paleoproterozoic (~2.02 Ga to ~1.96 Ga). The ~1.94 Ga carbonatite and ~1.85 Ga granitic dyke were formed by partial melting of marble and Meso- to Neoarchean basement rocks, respectively. Both of them were formed in post-collisional setting. The ~1.82 Ga mafic granulite recorded high-pressure granulite facies metamorphism followed by a medium–low pressure granulite facies metamorphic overprint, suggesting a clockwise P-T path and implying an environment of collisional orogenesis. The ~1.76 Ga A-type granite resulted from the reworked Neoarchean crust and was most likely related to a post-collisional episode. Combined with previous studies, we identify two Paleoproterozoic orogenic belts of the Dunhuang Block: the ~2.00–1.96 Ga South Orogen and ~1.85–1.80 Ga North Orogen. According to the coupling of these two orogenies with the Columbia orogeny, we conclude that the Dunhuang Block was associated with the assembly of the Columbia supercontinent.