Carboniferous Sedimentary Provenance And Tectonic Setting In The Darbut Region Of Western Junggar (Nw China): Evidence From Mineralogy, Geochemistry And Detrital Zircon U-Pb Dating

The Carboniferous tectonic evolution of Western Junggar is crucial to understanding the subduction-accretion process of the Central Asian Orogenic Belt, but the nature of this setting is still controversial. In this work, composite mineralogical, geochemical and detrital zircon U-Pb geochronological investigations have been conducted on Carboniferous clastic rocks in the Darbut region. The chemical compositions and sedimentary features show low sediment maturity and limited recycling, suggesting short-distance transportation and rapid accumulation. The samples contain igneous rock debris, mainly andesite and small amounts of basalt and granite, and a heavy mineral assemblage of Zr + Ap + Aug + Hbl + iron-bearing minerals (Hem-Lm, Ilm, Mag and Py). The samples feature moderate ratios of Zr/Sc (average 15.47) and Th/Sc (average 0.61), and low ratios of La/Sc, Co/Th and La/Th, as well as low Hf content, suggesting intermediate to felsic arc-related igneous provenances. Detrital zircon grains from the clastic rocks show prominent age peaks in the Devonian and Carboniferous with positive epsilon(Hf)(t) values, indicating a consistent provenance associated with the Tiechanggou-Halaalate island arc. Combining the petrology, geochemistry and geochronology of the sedimentary and magmatic rocks, we conclude that the Darbut Carboniferous volcanic-sedimentary strata were deposited in a back-arc basin during c. 327-311 Ma.