Sedimentary provenance in response to Carboniferous arc-basin evolution of East Junggar and North Tianshan belts in the southwestern Central Asian Orogenic Belt

摘要

The North Tianshan and East Junggar belts in north Xinjiang, China, are two key terranes for the Paleozoic tectonic reconstruction of the Central Asian Orogenic Belt (CAOB). However, their Carboniferous paleogeo-graphic setting and arc-basin relationships remain disputed. To better-constrain these problems, we carried out an investigation on the provenance of Carboniferous sandstones from the Yaomoliang Formation in East Junggar and the Qijiaojing Formation in North Tianshan. Modal and geochemical analyses reveal that the sediments are mainly derived from arc-related terranes. Detrital zircon U-Pb age spectra show distinct differences between the East Junggar and North Tianshan belts. The upper Yaomoliang Formation has a Late Carboniferous depositional age (ca. 315 Ma) with a single peak spectrum of detrital zircon ages, which is similar with zircon ages from the igneous rocks and associated accretionary complexes in East Junggar belt, suggesting that it was probably derived from the East Junggar arc. The samples from the Qijiaojing Formation have Early Carboniferous depositional ages (ca. 330 Ma to 354 Ma). Their complicated detrital zircon age peaks resemble the detrital and igneous zircon ages from the Harlik-Dananhu arc, implying that their source terrane could be the Harlik-Dananhu arc, as revealed by the near-source petrographic and arc-derived geochemical features. In combination with our results and the published data, we suggest two distinctive Carboniferous arc-basin systems, the Kelamaili Ocean-related arc-basin which is characterized by the northward subduction beneath the East Junggar arc, and the Bogda intraarc basin which evolved from splitting the previous Harlik-Dananhu arc by the rollback of the subducting North Tianshan oceanic plate. The sedimentary provenance evidence reveals that the Kelamaili Ocean has not closed until ca. 315 Ma. The multiple arc-basin systems in North Xinjiang indicate an archipelago-type subduction and accretionary scenario