Magmatic Records on the Late Paleozoic Tectonic Evolution of Western Junggar,Xinjiang

Carboniferous to Permian is a critical period for tectonic evolution of the Central Asian Orogenic Belt and formation of major metal ore deposits in the northern Xinjiang. As the western Junggar is a ore resource-rich area,its tectonic settings during that period have attracted wide attention. Previous researches on tectonics,ophiolite,sedimentary and igneous rocks indicate that there was ocean basin system and related subduction during the Late Carboniferous-Early Permian(290Ma) in Western Junggar. Since 290Ma Western Junggar evolved into collisional regime characterized by the formation of the Early Permian red molasse accompanying rapid crustal uplift,which suggest the termination of Junggar ocean system. The statistics of geochronological data indicate that the peak period of magmatic activities is 300～310Ma in Western Junggar. Voluminous granitoids of various types(A-type granites,charnockite I-type granites,adakite,magnesian diorite) formed in this period,and the isotopic data of these rocks suggest significant addition of juvenile material. We argue that this dramatic change was due to the onset of ridge subduction. This model supplies also a plausible explanation for mechanism of Cu-Au mineralization in the period. Moreover,ridge subduction was likely important for amalgamation and crustal growth in the CAOB.