The Geological Record of the Post-collision Shift to Intraplate System in West Junggar-Evidence from Kexike A-type Granite

Late Paleozoic A₁-type and A₂-type granitoids are widespread in West Junggar. The Kexike granite intruded into the Silurian-Carboniferous volcanic strata in the north of the Xiemisitai fault. Zircon LA-ICP-MS U-Pb dating on the Kexike granite yields weighted mean ²⁰⁶Pb/²³⁸U ages of 293.3±3.4Ma, corresponding to the Early Permian, implying the granite is the product of post-collisional magma activity around the Junggar area. Petrogeochemistry analyses suggest the Kexike pluton is characterized by high silica (SiO₂>68.6%), high alkaline (Na₂O+K₂O>8.63%), low titanium(TiO₂<0.48%), low calcium (CaO<1.48%), and relatively high alumina (Al₂O₃>13.56%), indicating shoshonite series of metaluminous or peraluminous (ACNK=0.95~1.11). The granites belong to A₁-A₂ granite of transition type, with relative high REE content (except for Eu), large ion lithophile elements such as Rb, high field strength elements such as Th, Hf and Zr, relative depletion in Ba, Sr, P and Ti. The sustainable magmatic evolution well recorded the two continuous tectonic evolutions, providing important evidence for demarcating the timing of the post-collision shift to intraplate system in West Junggar.