Abstract:There are a large number of late Paleozoic intermediate to acid intrusions exposed along the tectonic-magmatism belt of western Junggar Basin, Xinjiang. It is of great significance to know the magmatic evolution of this tectonic-magmatism belt through the petrogenesis and emplacement periods. However, there are still no accurate isotopic chronologic and geochemical data of partial small rock bodies, such as Kuergakexi granite, which has restricted the understanding of their genetic types and emplacement ages. In this paper, the petrogenic age and genetic type of Kuergakexi granite were investigated through field geological survey, LA-ICP-MS zircon U-Pb isotopic dating and geochemical analysis. The results show that Kuergakexi granite is mainly composed of granodiorite with an outcrop area of 0.55 km2, and prove that the zircons yielded a LA-ICP-MS U-Pb age of 312.9±2.9 Ma (n=20, MSWD=0.072), indicating that intrusive time of the granodiorite is the early Late Carboniferous. The values of major elements indicate that these granodiorites are characterized by high Si, intermediate Al and rich alkali, and low Mg, with A/CNK ratios ranging from 0.99 to 1.20. The trace elements are enriched in large ion lithophile elements such as Rb, Ba, K, but strongly depleted in high field strength elements such as Nb, Ta, Ti, P and heavy rare earth elements, with slightly negative Eu anomalies (δEu=0.68~0.82). These features suggest that the Kuergakexi granite belongs to calc-alkaline series, weakly peraluminous I-type granite. A comparison between Kuergakexi granite and other small intrusions such as Bieluagaxi granite and Baogutu granite shows that they have significant similarities in petrogenic age and geochemical characteristics. It is thus held that the Junggar Ocean continued its deep subduction from the south to the north during the early Late Carboniferous. The source of the granodiorite might have been the lower juvenile crust derived from the depleted mantle that had been metasomatized by fluids released from subduction slabs.
