青海南山沟后岩浆杂岩体锆石U-Pb年代学、岩石成因及其地质意义

发布时间：2018-05-26 01:41

本文选题：青海南山 + 西秦岭北缘　；参考：《大地构造与成矿学》2017年05期

【摘要】：青海南山构造带是衔接宗务隆构造带、南祁连构造带和西秦岭造山带的重要结合带。沟后岩浆杂岩体位于青海南山构造带东段,主要由辉长岩、辉长闪长岩、石英闪长岩、花岗闪长岩组成。本文对沟后岩浆杂岩体进行了详细的岩石学、岩石地球化学和LA-ICP-MS锆石U-Pb同位素年代学研究。结果表明,辉长岩、辉长闪长岩、石英闪长岩、花岗闪长岩及暗色微粒包体的结晶年龄分别为248.8±2.6 Ma、243.2±2.1 Ma、243.1±0.9 Ma、244.0±2.1 Ma和249±3 Ma。辉长岩富铁、镁,贫碱;辉长闪长岩高铝、富钙和钠,二者均为钙碱性岩类。石英闪长岩和花岗闪长岩为准铝-弱过铝质高钾钙碱性岩,暗色微粒包体属钙碱性-碱性岩系列。不同岩石类型均表现为富集大离子亲石元素(Cs、Rb、K)和Pb,亏损高场强元素(Nb、Ta、Ti)和P、Ba负异常;稀土元素配分曲线均具有轻重稀土分异的右倾特征,具弱-中等负Eu异常。岩相学和岩石地球化学特征表明沟后岩浆杂岩体具壳幔岩浆混合特征,暗示其可能形成于由俯冲流体交代地幔楔部分熔融的幔源岩浆底侵作用下的构造环境。辉长岩为幔源岩浆经分离结晶的产物,辉长闪长岩为幔源岩浆经分异演化并混染少量壳源岩浆的产物;中基性岩浆与壳源中酸性岩浆发生混合并经历一定的分异演化过程形成了石英闪长岩和花岗闪长岩。结合区域地质资料分析认为,沟后岩浆杂岩体可能代表了研究区早三叠世晚期-中三叠世早期宗务隆洋向南消减作用相关的构造岩浆事件。
[Abstract]:The Nanshan tectonic belt in Qinghai is an important conjunctive zone connecting Zongwu uplift tectonic belt, South Qilian tectonic belt and West Qinling orogenic belt. The Gouhou magmatic complex is located in the eastern segment of the Nanshan tectonic belt in Qinghai Province and is mainly composed of gabbro, pyroxenite, quartz diorite and granodiorite. In this paper, detailed petrology, geochemistry and U-Pb isotopic chronology of LA-ICP-MS zircon have been carried out for the Gouhou magmatic complex. The results show that the crystallization ages of gabbro, pyrodiorite, quartz diorite, granodiorite and dark particle inclusions are 248.8 卤2.6 Ma-243.2 卤2.1 Ma-243.1 卤0.9 Ma-244.0 卤2.1 Ma and 249 卤3 Ma, respectively. Gabbro is rich in iron, magnesium and alkali, and pyroxenite is high in aluminum, calcium and sodium, both of which are calc-alkaline. Quartz diorite and granodiorite are quasi-aluminum-weakly peraluminous high-potassium calc-alkaline rocks, and the dark particle inclusions belong to the calc-alkaline rock series. The different rock types are characterized by enrichment of large ion lithophile elements (Cslr Rbtl K) and Pb, and depletion of high field strength elements (NbTX Tatii) and PnbBa negative anomalies, and the REE partition curves all have the characteristics of right deviation of REE differentiation and weak to medium negative EU anomalies. The petrographic and petrogeochemical characteristics indicate that the Gouhou magmatic complex is characterized by a mixture of crust-mantle magma, suggesting that it may have been formed in a tectonic environment in which mantle magma submersed by subducting fluid metasomatic mantle wedge partially melted. Gabbro is the product of the separation and crystallization of mantle-derived magma, while the amphiolite is the product of the differentiation and evolution of mantle-derived magma and mixed with a small amount of crust-derived magma. The intermediate-basic magma and crust intermediate-acid magma mix and undergo a process of differentiation and evolution to form quartz diorite and granodiorite. Based on the analysis of regional geological data, it is concluded that the Gouhou magmatic complex may represent the tectonic magmatic events related to the subduction of Zongwulong ocean in the late early Triassic to the early Middle Triassic in the study area.
【作者单位】：西部矿产资源与地质工程教育部重点实验室国土资源部岩浆作用成矿与找矿重点实验室长安大学地球科学与资源学院;山东理工大学资源与环境工程学院;中国地质大学(北京)地球科学与资源学院;南阳理工学院土木工程学院;
【基金】：国家自然科学基金(41472191、41502191、41172186) 中国地质调查局地质调查项目(12120114041201、12120114018219) 中央高校基本科研业务费专项资金(CHD2011TD020、2013G1271091、2013G1271092)联合资助
【分类号】：P581;P597.3

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