东昆仑阿牙克库木湖北巴什尔希花岗岩锆石LA-ICP-MS U-Pb定年及其地质意义

Zircon LA-ICP-MS U-Pb dating and geological significance of Bashierxi granite in the eastern Kunlun area,China

巴什尔希岩体分布在东昆仑西段白干湖断裂和阿尔金断裂之间,岩性主要为二长花岗岩和钾长花岗岩,其中二长花岗岩与白干湖钨、锡多金属矿床关系密切。对锆石内部结构、阴极发光图像特征和Th/U比值的研究表明,二长花岗岩中的锆石为岩浆锆石。锆石LA-ICP-MSU-Pb同位素分析结果显示,二长花岗岩形成年龄为(458.0±9.0)Ma。结合前人对巴什尔希钾长花岗岩的锆石U-Pb定年(432.3±0.8)Ma,初步认为该岩体为晚奥陶世—早志留世侵入体。元素地球化学特征显示,巴什尔希花岗岩为弱准铝质或弱过铝质A型花岗岩,是东昆仑地区加里东期局部弧后盆地拉张过程中,地幔底侵导致地壳物质熔融的产物。

The Bashierxi pluton is located in the western segment of the eastern Kunlun, between Baiganhu fault and Aerjin fault, this pluton mainly consists of monzonitic granite and K-feldspar granite, and the monzonitic granite is closely related with the ore-forming process of the Baiganhu tungsten-fin deposit. The internal structures, cathodeluminescence （CL） images and Th/U ratios of the zircon grains from the monzonific granite reveal that these zircon grains have typical characteristics of magmatic zircon. The LA-ICP-MS analyses show that the zircon grains from the monzonitic granite have concordant U-Pb ages of （458.0±9.0）Ma, on the other hand, the zircon grains from the K-feldspar granite have U-Pb ages of （432.3±0.8）Ma, these data indicated that the Bashierxi pluton is a intrusion formed from Late Ordovician to Early Silurian. Major and trace element data of the monzonitic granite show that Bashierxi granite is weakly metaluminous or peraluminous A-type granite. These rocks were considered as melts derived from crustal source during back-arc basin extension in eastern Kunlun, and the early Baiganhu tungsten-tin deposit era is represented by the ages of monzonitic granite.