南阿尔金玉苏普阿勒克塔格花岗质复式岩体岩石成因与构造地质意义研究

发布时间：2019-01-10 12:58

【摘要】：玉苏普阿勒克塔格花岗质复式岩体位于阿尔金造山带南缘,是南阿尔金出露面积最大的花岗岩体之一。根据野外地质调查,该岩体是多期岩浆分期侵位形成,两期岩体的结构构造与物质组成具有明显的差异,并含有大量的暗色包体。这为我们探讨岩浆演化和深部壳幔相互作用提供了很好的条件,同时也为我们探讨南阿尔金古生代岩浆作用与构造演化的关系提供了可能。然而到目前为止尚未见到该岩体详细的研究成果发表。因此,本文选择该复式岩体为研究对象,通过对该复式岩体的野外地质及矿物学、岩石学、地球化学等特征进行对比研究,探讨岩体的成因及形成的动力学过程。结合锆石U-Pb年代学及Lu-Hf同位素组成,判断岩体形成的时代、物质来源及成因类型。最后综合前人对南阿尔金岩浆活动期次的划分,探讨该岩体的构造地质意义。玉苏普阿勒克塔格花岗质复式岩体主体为中粗粒似斑状黑云二长花岗岩,是第一期岩浆侵位的结果。在岩体边部与地层的构造接触带上出露少量中细粒含斑黑云二长花岗岩,含有钾长石斑晶及暗色包体,是第二期岩浆侵位的结果。主量元素特征显示玉苏普阿勒克塔格花岗岩体为高钾钙碱性I型花岗岩,第一期岩体比第二期岩体相对富铁镁,贫硅。微量元素特征显示第一期岩体比第二期岩体相对亏损高场强元素,富集大离子亲石元素。稀土元素特征显示该复式岩体具有轻稀土富集、重稀土亏损的右倾式配分模式,具有Eu的负异常。据锆石LA-MC-ICP-MS U-Pb同位素定年,获得第一期岩体的年龄为(458.4±4)Ma,第二期岩体的年龄为(418.2±3.6)Ma,说明该复式岩体的形成时代为早古生代,第一期岩体形成相对较早,为两期岩浆分期侵位的结果。Hf同位素组成显示该复式岩体整体ε_(Hf)(t)值为正值,表明该复式岩体来源于新生地壳的部分熔融,第一期花岗岩体的ε_(Hf)(t)值相对更高,说明形成第一期岩体的岩浆混合作用程度更高。综合上述研究结果,我们认为南阿尔金地区从460Ma开始进入造山晚期阶段。南阿尔金洋向北的俯冲、碰撞减弱,直至420Ma左右进入碰撞后的均衡调整、伸展阶段。在这个过程中,南阿尔金洋壳的俯冲板片脱水,流体交代上覆楔形地幔,地幔楔部分熔融形成玄武质岩浆。该玄武质岩浆带来的热量及流体使新生地壳部分熔融,在地壳深部形成花岗质岩浆房。该岩浆经历岩浆混合作用及岩浆分异作用后分期侵位,从而形成玉苏普阿勒克塔格花岗质复式岩体。
[Abstract]:The Yussup Alektagic granitic complex is located in the southern margin of the Altun orogenic belt and is one of the largest granite bodies in the southern Altun. According to the field geological investigation, the rock mass was formed by stages of magma emplacement. The structure, structure and material composition of the two stages are obviously different, and there are a large number of dark inclusion bodies. This provides a good condition for us to study magmatic evolution and deep crust-mantle interaction, and also provides a possibility for us to study the relationship between Paleozoic magmatism and tectonic evolution in South Altun. However, no detailed research results have been published so far. Therefore, this paper chooses the complex rock mass as the research object, through the comparative study of the field geology, mineralogy, petrology, geochemistry and other characteristics of the complex rock mass, discusses the origin of the rock mass and the dynamic process of its formation. Combined with zircon U-Pb chronology and Lu-Hf isotopic composition, the age, material source and genetic type of the rock mass are determined. Finally, the tectonic and geological significance of the rock mass is discussed by synthesizing the division of the magmatic activity stages of the South Altun. The main body of the Yusupu Alektagg granitic complex is the medium coarse grained porphyry black cloud monzonitic granite, which is the result of the first magma emplacement. In the tectonic contact zone between the edge part of the rock mass and the strata, a small number of medium-fine granites containing porphyry granites, potash feldspar porphyry and dark inclusion are exposed, which is the result of the second stage of magma emplacement. The main element characteristics show that the Yushupu Alektage granite body is a high potassium calc-alkaline I-type granite. The first stage of the rock mass is relatively rich in iron and magnesium and is poor in silicon compared with the second stage of the rock mass. The characteristics of trace elements show that the first stage of rock mass is relatively depleted of high field strength elements compared with the second stage of rock mass, and it is rich in large ion lithophile elements. The characteristics of rare earth elements show that the complex rock mass is characterized by light rare earth enrichment, heavy rare earth depletion, right tilting distribution model and negative Eu anomaly. According to zircon LA-MC-ICP-MS U-Pb isotopic dating, the age of the first stage of the rock mass is (458.4 卤4) Ma, and the age of the second stage of the rock mass is (418.2 卤3.6) Ma, which indicates that the complex rock mass was formed in the early Paleozoic. The formation of the first stage of the rock mass is relatively early, which is the result of two magma emplacement stages. The Hf isotopic composition shows that the integral 蔚 _ (Hf) (t) value of the complex rock mass is positive, which indicates that the complex rock body originated from the partial melting of the new crust. The 蔚 _ (Hf) (t) value of the first stage granite body is higher than that of the first stage granite body, which indicates that the magmatic mixing degree of the first stage granite body is higher. Based on the above results, we believe that the southern Altun area has entered the late orogenic stage from 460Ma. The southern Altun ocean subducts northward and the collision weakens until 420Ma enters the postcollision equilibrium adjustment and extension stage. During this process, the subduction plate of the southern Altun oceanic crust was dehydrated, fluid metasomatic overlying the wedge mantle, and the mantle wedge partially melted to form Black Tortoise magma. The heat and fluid from the Black Tortoise magma partially melt the new crust and form a granitic magma chamber in the deep crust. The magma underwent magma mixing and magmatic differentiation, and then emplaced by stages, thus forming the Yusupu Alektagg granitic complex.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.1;P548

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