喜马拉雅碰撞造山带新生代地壳深熔作用与淡色花岗岩

发布时间：2018-02-08 22:40

本文关键词： 淡色花岗岩高分异花岗岩地壳深熔作用碰撞造山带喜马拉雅造山带　出处：《岩石学报》2017年05期 　论文类型：期刊论文

【摘要】：自从印度-欧亚大陆碰撞以来,伴随着构造演化和温度-压力-成分(P-T-X)的变化,喜马拉雅造山带中下地壳变质岩发生不同类型的部分熔融反应,形成性质各异的过铝质花岗岩。这些花岗岩在形成时代、矿物组成、全岩元素和放射性同位素地球化学特征上都表现出巨大的差异性。始新世构造岩浆作用形成高Sr/Y二云母花岗岩和演化程度较高的淡色花岗岩和淡色花岗玢岩,它们具有相似的Sr-Nd同位素组成,是碰撞早期增厚下地壳部分熔融的产物。渐新世淡色花岗岩主要为演化程度较高的淡色花岗岩,可能指示了喜马拉雅造山带的快速剥露作用起始于渐新世。早中新世以来的淡色花岗岩是喜马拉雅造山带淡色花岗岩的主体,是变泥质岩部分熔融的产物,包含两类部分熔融作用——水致白云母部分熔融作用(A类)和白云母脱水熔融作用(B类)。这两类部分熔融作用形成的花岗质熔体在元素和同位素地球化学特征上都表现出明显的差异性,主要受控于两类部分熔融作用过程中主要造岩矿物和副矿物的溶解行为。这些不同期次的地壳深熔作用都伴随着高分异淡色花岗岩,伴随着关键金属元素(Nb、Ta、Sn、Be等)的富集,是未来矿产勘探的重要靶区。新的观测结果表明:在碰撞造山带中,花岗岩岩石学和地球化学性质的变化是深部地壳物质对构造过程响应的结果,是深入理解碰撞造山带深部地壳物理和化学行为的重要岩石探针。
[Abstract]:Since the India-Eurasian collision, different types of partial melting reactions have occurred in the lower crust metamorphic rocks in the Himalayan orogenic belt, following tectonic evolution and changes in temperature, pressure and composition (P-T-X). Forming peraluminous granites of various natures. These granites were formed at the time of their formation, mineral composition, The geochemical characteristics of the whole rock elements and radioisotopes show great differences. The Eocene tectonic magmatism resulted in the formation of high Sr/Y dimica granites and higher evolutional degree of pale granite and pale granite-porphyrite. They have similar Sr-Nd isotopic composition and are the product of partial melting of the lower crust thickened in the early collision period. It may indicate that the rapid exfoliation of the Himalayan orogenic belt began in the Oligocene. The pale granite since the early Miocene is the main body of the pale granite in the Himalayan orogenic belt and the product of partial melting of the argillaceous rocks. There are two kinds of partial melting processes: water induced partial melting of Muscovite and dehydration of Muscovite and dehydration of Muscovite. The granitic melts formed by these two kinds of partial melting processes have both elemental and isotopic geochemical characteristics. Showing obvious differences, It is mainly controlled by the dissolution behavior of the major petrogenic minerals and accessory minerals in the process of two types of partial melting. These deep crustal meltdowns are accompanied by the enrichment of high grade heterogenous pale granites and the key metal elements, such as NbTa-TaSn-SnBe, and so on, which are mainly controlled by the dissolution behavior of the major rock-forming minerals and parametals during the process of partial melting. The new observation results show that in the collisional orogenic belt, the changes of granite petrology and geochemistry are the result of the deep crustal material responding to the tectonic process. It is an important rock probe for deep understanding of the physical and chemical behavior of the deep crust of the collision orogenic belt.
【作者单位】：中国地质科学院地质研究所;
【基金】：中国地质调查局地质调查项目(121201102000150005) 公益性行业科研专项(201511022) 国家自然科学基金项目(41425010)联合资助
【分类号】：P542;P588.121

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