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青海冷湖北片麻状石英闪长岩Si O2含量较低、Na2O、Al2O3、Mg O含量较高,铝饱和指数(ASI)介于0.66~0.70,具准铝质岩石的特征,属高钾钙碱性系列。球粒陨石标准化的稀土元素配分曲线表现为轻稀土富集型,轻重稀土分馏明显,Eu呈很弱的负异常(δEu=0.82~0.87)。微量元素地球化学特征显示,岩石富集大离子亲石元素Rb、Ba、Sr和Th、U,贫高场强元素Nb,Ta、Zr、Hf等,显示出与板块俯冲作用有关的造山带岩浆岩的特征,岩石形成于火山弧构造环境。青海冷湖北片麻状石英闪长岩形成于以角闪石作为主要残余的压力环境下,源岩可能为中—高钾的变质玄武岩。经过锆石阴极发光分析和MC-LA-ICP-MS锆石U-Pb测年,获得加权平均年龄为430.7±0.8Ma,代表了片麻状石英闪长岩的成岩年龄。该岩体是在塔里木地块与柴达木地块发生斜向俯冲碰撞时,深部软流圈相对岩石圈继续运动,岩石圈内部发生拆离,密度相对较小的柴达木陆壳在浮力作用下迅速折返,随着温度的升高或者压力的降低,陆壳中—高钾变玄武岩在中下地壳压力条件下发生熔融形成,是柴北缘高压—超高压变质带折返的物质响应。
The content of Si2O in the Lenghu northern gneissic quartz diorite is relatively low with high contents of Na2O, Al2O3, MgO and aluminum saturation index (ASI) ranging from 0.66 to 0.70. It is characterized by high-K Alkaline series. The normalized REE distribution curve for chondrite is characterized by light rare earth enrichment, obvious fractionation of light and heavy rare earths and very weak negative Eu anomaly (δEu = 0.82 ~ 0.87). Trace element geochemical characteristics show that the rocks are enriched in large ion lithophile elements such as Rb, Ba, Sr and Th, U, high field strength elements Nb, Ta, Zr, Hf, etc., indicating that the orogenic magmatism associated with plate subduction Rock characteristics, the rock formed in the volcanic arc tectonic environment. The Qinghuobei gneissic quartz diorite in Qinghai Province was formed under the pressure environment with amphibole as the main residual. The source rocks may be medium-high potassium metamorphic basalts. After zircon cathodoluminescence analysis and MC-LA-ICP-MS zircon U-Pb dating, the weighted average age was 430.7 ± 0.8Ma, representing the diagenetic age of gneissic quartz diorite. In the event of oblique subduction collisions between the Tarim block and the Qaidam block, the deep asthenosphere continues to move relative to the lithosphere and detachment occurs within the lithosphere. The Qaidam continental crust with a relatively small density is in buoyancy Under the action of rapid reenforcement, the medium-high-K transitional basalt melts under the conditions of middle and lower crustal pressure with the increase of temperature or pressure, which is the material response of the reenforcement of the HP-UHP metamorphic belt in the northern Qaidam.