Abstract

The Carboniferous tectonic evolution of Western Junggar is crucial to understanding the subduction-accretion process of the Central Asian Orogenic Belt (CAOB), 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 contents, 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 εHf(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 ∼327-311Ma.

Supplementary material:https://doi.org/10.6084/m9.figshare.c.5357293

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