Zircon U-Pb age and its geological significance of the igneous rocks from Batamayineishan Formation in East Junggar

The Batamayineishan Formation and Shigiantan Formation that range in Shuangjingzi area ( within East Junggar) have been studied through thin section authentication, geochemical analysis, zircon U-Pb dating and conodonts selection. The results show that the formation time of Batamayineishan volcanic rocks began at 348. 7 +/- 2. 9Ma and ended after 318. 7 +/- 4. 2Ma, the only intrusive rock formed at 255. 9 +/- 3. 5Ma. The rocks commonly have captured zircons which have the characteristics of magmatic zircon and whose ages range from Carboniferous Tournaisian to Precambrian (354. 7 similar to 971. 2Ma). The ages of these captured zircons are similar to the ages of the island arc igneous rocks and ophiolites developed around the basin. Besides, four complete conodonts that belong to Idiognathodus and Streptognathodus have been found in the limestone of Shigiantan Formation. On the basis of this, we get the following understanding by collecting and sorting out the previous data : (1) The volcanic rocks of the Batamayineishan Formation are diachronous, whose ages range from the Early Carboniferous (348.7 +/- 2. 9Ma) to the Late Carboniferous (300.4 +/- 1. 3Ma) ; (2) The Shigiantan Formation which is located on the Batamayineishan Formation formed at Late Carboniferous after 318. 7 +/- 4. 2Ma; (3) The closure time of Junggar ocean which is represented by Kalamaili suture belt was between Famennian of Late Devonian and 348. 7Ma; (4) The basement of the Junggar basin may be composed of island arc and oceanic crust, and there is a Precambrian basement. This study aims to determine the formation time of Batamayineishan Formation and Shigiantan Formation and provide evidences for solving the scientific problems such as closing time of Kalamaili Ocean and basement features of Junggar Basin.