Mesoproterozoic Pashtok diorite intrusive sequence on the northern margin of West Kunlun orogenic belt in Xinjiang and its geological implications

Анотація

Pashtok intrusive sequence, located in the southwestern margin of the Tarim Block and the northern margin of the West Kunlun orogenic belt, is composed of quartz diorite and quartz monzonitic diorite, which is similar to TTG combination. It was formed in the late Mesoproterozoic. Large quantities of data prove that the strata and rocks located in the northern edge of West Kunlun orogenic belt still retain the records of orogenic events, plate subduction and convergence at the end of Mesoproterozoic, and they confirm that late Mesoproterozoic southwestern Tarim paleoplate belongs to the present active continental margin. Tarim ancient block was a part of Rodinia supercontinent. The early Paleozoic closure of the Kuda Ocean was closely related to the subduction between Kuda crust and Tarim ancient block. At the beginning of geochemical analysis, main elements and trace elements of Pashtok intrusive sequence were studied in detail. A discussion was made concerning the genesis of the intrusive sequence, the tectonic setting and the geodynamic model between plates around the intrusive sequence. The research shows that Pashtok intrusive sequence is of the I-type metaluminous high-K calc-alkaline granodiorite series, which belongs to continental arc granitoids of active continental margin. The intrusive sequence is divided into two intrusive periods. Both periods of intrusive rocks experienced comagmatic evolution, and the parental magma was a mixture of crustal materials and mantle magma, which gradually evolved into more acidic magma. Based on physical environment and tectonic setting in the course of magmatic evolution, the authors have reached the conclusion that the subduction of the Kuda Ocean crust brought about the closure of the Kuda Ocean and the convergence between Tarim ancient block and Qaidam ancient block which were pieced together and gradually became a part of the Rodinia supercontinent.

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