Zircon U–Pb ages and tectonic implications of Paleozoic plutons in northern West Junggar, North Xinjiang, China

North Xinjiang, Northwest China, is made up of several Paleozoic orogens. From north to south these are the Chinese Altai, Junggar, and Tian Shan. It is characterized by widespread development of Late Carboniferous–Permian granitoids, which are commonly accepted as the products of post-collisional magmatism. Except for the Chinese Altai, East Junggar, and Tian Shan, little is known about the Devonian and older granitoids in the West Junggar, leading to an incomplete understanding of its Paleozoic tectonic history. New SHRIMP and LA-ICP-MS zircon U–Pb ages were determined for seventeen plutons in northern West Junggar and these ages confirm the presence of Late Silurian–Early Devonian plutons in the West Junggar. New age data, combined with those available from the literature, help us distinguish three groups of plutons in northern West Junggar. The first is represented by Late Silurian–Early Devonian (ca. 422 to 405 Ma) plutons in the EW-striking Xiemisitai and Saier Mountains, including A-type granite with aegirine–augite and arfvedsonite, and associated diorite, K-feldspar granite, and subvolcanic rocks. The second is composed of the Early Carboniferous (ca. 346 to 321 Ma) granodiorite, diorite, and monzonitic and K-feldspar granites, which mainly occur in the EW-extending Tarbgatay and Saur (also spelled as Sawuer in Chinese) Mountains. The third is mainly characterized by the latest Late Carboniferous–Middle Permian (ca. 304 to 263 Ma) granitoids in the Wuerkashier, Tarbgatay, and Saur Mountains. As a whole, the three epochs of plutons in northern West Junggar have different implications for tectonic evolution. The volcano-sedimentary strata in the Xiemisitai and Saier Mountains may not be Middle and Late Devonian as suggested previously because they are crosscut by the Late Silurian–Early Devonian plutons. Therefore, they are probably the eastern extension of the Early Paleozoic Boshchekul–Chingiz volcanic arc of East Kazakhstan in China. It is uncertain at present if these plutons might have been generated in either a subduction or post-collisional setting. The early Carboniferous plutons in the Tarbgatay and Saur Mountains may be part of the Late Paleozoic Zharma–Saur volcanic arc of the Kazakhstan block. They occur along the active margin of the Kazakhstan block, and their generation may be related to southward subduction of the Irtysh–Zaysan Ocean between Kazakhstan in the south and Altai in the north. The latest Late Carboniferous–Middle Permian plutons occur in the Zharma–Saur volcanic arc, Hebukesaier Depression, and the West Junggar accretionary complexes and significantly postdate the closure of the Irtysh–Zaysan Ocean in the Late Carboniferous because they are concurrent with the stitching plutons crosscutting the Irtysh–Zaysan suture zone. Hence the latest Late Carboniferous–Middle Permian plutons were generated in a post-collisional setting. The oldest stitching plutons in the Irtysh–Zaysan suture zone are coeval with those in northern West Junggar, together they place an upper age bound for the final amalgamation of the Altai and Kazakhstan blocks to be earlier than 307 Ma (before the Kaslmovian stage, Late Carboniferous). This is nearly coincident with widespread post-collisional granitoid plutons in North Xinjiang.