论文部分内容阅读
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。
The Nanshan tectonic belt of Qinghai is an important combination belt that connects the Zongloung tectonic belt, the southern Qilian tectonic belt and the West Qinling orogenic belt. The post-ditch magmatic complex is located in the eastern segment of the Nanshan structural belt in Qinghai Province and consists mainly of gabbro, gabbro, quartz diorite and granodiorite. In this paper, detailed petrological, lithogeochemical and zircon U-Pb isotopic dating of zircons from the ditch magma complex have been studied. The results show that the crystallization ages of gabbro, gabbro, quartz diorite, granodiorite and dark particle inclusions are 248.8 ± 2.6 Ma, 243.2 ± 2.1 Ma, 243.1 ± 0.9 Ma and 244.0 ± 2.1 Ma and 249 ± 3 Ma. The gabbro is rich in iron, magnesium and lean alkali; the gabbro diorite is high in aluminum, rich in calcium and sodium, both of which are calc-alkaline rocks. Quartz diorite and granodiorite are quasi-aluminum-weakly permafrost calc-alkaline rocks, and dark-colored granulite inclusions are calc-alkaline-alkaline rocks. All rock types are enriched in large ion lithophile elements (Cs, Rb, K) and Pb, depleted high field strength elements (Nb, Ta and Ti) and P and Ba negative anomalies. The rightward divergence feature, with a weak-medium negative Eu anomaly. Petrography and lithogeochemical characteristics show that the post-sulcal magmatism is characterized by crust-mantle magmatism suggesting that it may be formed under the mantle-derived magma underplating due to partial melting of subducted fluid mantle wedges. The gabbro is the product of the separation and crystallization of mantle magma. The gabbro is the product of mantle magmatic differentiation and mixed with a small amount of crustal magma; the mafic magma mixed with the acidic magma in the crust and experienced A certain differentiation and evolution process formed the quartz diorite and granodiorite. According to the analysis of regional geological data, the post-ditch magmatic complex may represent the tectono-magmatic events related to the southward depletion of the Chongzonglong Ocean from the Late Triassic to Early Middle Triassic in the study area.