Tectonic settings of A-type granites of Shaerdelan area, southeastern margin of Junggar block, Xinjiang, western China
准噶尔板块东南缘沙尔德兰地区A型花岗岩构造环境研究

Two kinds of A-type granites, moyite and orthoclase granite porphyry, located at the southeastern margin of Junggar block, which is generally named north Tianshan Mountain, Xinjiang,western China. The Kotaclicnircon moyite lies in the South Lake island arc belt, the Baiponan moyite and orthoclase granite-porphyry lie in the Qoltag-Red flag mountain trench-arc belt. Both Baiponan moyite and Kotaclicnircon moyite belong to the high-K calc-alkaline series, they are enriched in light rare earth elements and high strength field elements, and obviously depleted in Nb and TiO2, and relatively depleted in Zr, Hf and P2O5, which are consistent with geochemical characters of volcanic arc granites. The orthoclase granite-porphyry belongs to High-K, calc-alkaline series. They are slight fractionation between LREE and HREE, and enriched in high strength field elements, relatively depleted in Ba, Sr, P2O5 and TiO2, which are consistent with the characters of within-plate granites. According to the classification diagrams of A-type granite, both moyite and orthoclase granite porphyry belong to A2 sub-type. Based on the reliable studies on north Xinjiang area and our research, the tectonic setting transition from island arc to lithosphere stretching settings of post-collision could be constrained to 320Ma The zircon SHRIMP U-Pb concordant age of the Baiponan moyite, and the orthoclase granite-porphyry are 338.3±4.3Ma and 278±2Ma respectively. Therefore, geochemical characters and geochronolog suggest that the Baiponan moyite should formed in island arc setting of B-type subduction, while the orthoclase granite-porphyry should formed in post-collision tectonic settings. These indicate that the A2-granite could form not only in non-orogenic and post-collision tectonic settings, but also in island arc settings.