Tectonic setting of the greywackes from the Permian Shenxianwan Formation in the Daftar area, Taxkorgan, Xinjiang

The Permian Shenxianwan Formation as the abyssal flysch deposits in the Daftar area, Taxkorgan, Xinjiang is located in the southern part of the Ta' axi tectonic mélange zone. The clastic sedimentary rocks primarily consist of greywacke. The source rocks are poorly transported and sorted, and thus have low maturity. The REE distribution patterns for the greywackes display the LREE enrichment and markedly negative Eu anomalies, indicating the close similarity to those of typical post-Archean shales and the upper continental crust. The trace element contents in the greywackes also approach those in the upper continental crust, suggesting that the greywackes are derived from the upper continental crust. The presence of abundant felsic rocks and minor amount of sedimentary rocks shows that the parent rocks of the greywackes were formed in the deep-sea anaerobic environments. The tectonic settings of the provenances of the greywackes are dominantly composed of the continental island arcs, with subordinately the active continental margins. The Lower to Middle Permian Shenxianwan Formation is interpreted as the rift basin deposits.