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欧龙布鲁克地块西北缘青海冷湖北片麻状花岗闪长岩SiO_2、MgO含量较低,Al_2O_3、Na_2O、CaO含量较高,铝饱和指数(ASI)为0.79~0.92,属高钾钙碱性系列。球粒陨石标准化稀土元素配分曲线表现为轻稀土元素富集型,轻、重稀土元素分馏明显,Eu呈弱的负异常(δEu=0.82~0.90)。微量元素地球化学特征显示,岩石富集大离子亲石元素Rb、Th和U,弱亏损高场强元素Nb、Ta、Zr等,显示出与板块俯冲作用有关的造山带岩浆岩的特征。青海冷湖北片麻状花岗闪长岩为角闪岩相压力条件下变玄武质岩石部分熔融的产物。LA-ICP-MS锆石206Pb/238Pb年龄为470.2±1.2Ma(n=19,MSWD=0.68),代表片麻状花岗闪长岩的成岩年龄。结合区域地质演化特征认为,该岩体形成于火山弧构造环境,是早奥陶世北阿尔金洋壳向欧龙布鲁克地块俯冲作用的地质记录。
On the northwestern margin of the Oolongbuluke Block, the gneissic granodiorite in the north of Lenghuo Lake in Qinghai Province has a lower content of SiO_2 and MgO, a higher content of Al_2O_3, Na_2O and CaO, and an aluminum saturation index (ASI) of 0.79 ~ 0.92. Sex series. The normalized REE distribution curve of chondrite is characterized by light rare earth element (REE) enrichment. The light and heavy rare earth elements are fractionally fractionated and Eu shows weak negative anomaly (δEu = 0.82 ~ 0.90). The trace element geochemical characteristics show that the rocks are enriched in large ion lithophile elements Rb, Th and U, and weak depleted high field strength elements Nb, Ta, Zr etc, indicating the characteristics of orogenic magmatism associated with plate subduction. The gneissic granodiorite from North Lenghuo Lake in Qinghai is the product of partial melting of the basaltic rocks under amphibolite facies pressure. The LA-ICP-MS zircon 206Pb / 238Pb is 470.2 ± 1.2 Ma (n = 19, MSWD = 0.68) and represents the diagenetic age of gneissic granodiorite. According to the regional geological evolution characteristics, the rock mass is formed in volcanic arc tectonic setting and is a geological record of the subduction of the northern Ordovician oceanic crust to the Oolongbrook Block.