塔里木北缘—南天山地区古生代侵入岩年代学、成因及构造意义

发布时间：2018-05-02 11:07

  本文选题：塔里木北缘 + 南天山　； 参考：《中国地质大学(北京)》2017年博士论文

【摘要】：塔里木北缘-南天山地区位于塔里木克拉通与中亚造山带过渡地带,构造位置十分关键。但就南天山洋俯冲极性、闭合时代以及地壳深部物质组成等关键问题上还存在争议。本文以塔里木北缘-南天山东部地区若干古生代侵入体为研究对象,在详细的野外地质调查基础上,以岩相学、矿物学、岩石地球化学及锆石U-Pb年龄、Hf同位素为主要研究手段,对岩体成因、构造演化及地壳深部物质组成进行了综合研究,取得以下认识:1、初步厘定了塔里木北缘-南天山地区古生代岩浆活动期次依据新获得的锆石U-Pb年龄和前人研究成果统计分析,古生代岩浆活动主要作用在晚奥陶世、中志留世至中泥盆世和晚石炭世至中二叠世三个时间段。其中,晚奥陶世的岩浆活动相对较弱,侵入体分布规模较小,而中志留世-中泥盆世(峰期年龄420 Ma)和晚石炭世-中二叠世(峰期年龄284 Ma)两期岩浆活动规模相对较大,以花岗质侵入岩为主,构成塔里木北缘-南天山地区古生代岩浆活动的主体。2、探讨了塔里木北缘-南天山地区东段古生代侵入岩成因及构造背景古生代中期岩石类型包括辉长岩、闪长岩和花岗岩。辉长岩体形成时代为晚志留世到早泥盆世(424±4 Ma和416±4 Ma),具有相对高的MgO和Mg#值(49-53),以及正的εHf(t)值(+4.0~+11.4),富集大离子亲石元素,亏损高场强元素,暗示其母岩浆源自俯冲板片流体改造的亏损地幔楔部分熔融;闪长岩体侵位时代为早泥盆世(415±2Ma),具有与辉长岩类似的地球化学特征及正的εHf(t)值(+3.0~+9.4),表明其源于亏损地幔的玄武质岩浆的分离结晶作用;花岗岩体形成于早泥盆世到中泥盆世(408~385Ma),均属于高钾钙碱性弱过铝质I型花岗岩,物质来源主要为年轻物质,或者不同程度新老物质的混合物源。不同类型的岩石,在区域上均表现出类似于安第斯型大陆弧岩石的地球化学特征,说明在古生代中期塔里木北缘为活动大陆边缘。古生代晚期岩体主要为花岗质岩体,岩体成因类型上具有A型,I型和S型花岗岩共存的特征。库尔楚II号花岗岩体(311±4 Ma),具有A型花岗岩特征,明显不同于俯冲带上形成的花岗岩,指示了其形成于后碰撞环境。从时间上来看,从库尔楚II号岩体、七个星晚期侵入体到盲起苏岩体(311~302Ma),源区形成深度不断增加(如Sr从91.9→192.8→592.5ppm),地壳逐渐加厚。之后形成的花岗岩(300~290 Ma)则具有低Sr(58.6~67.4ppm)和高Y(15.9~19.4ppm)的特征,暗示后碰撞阶段拆沉作用的发生,岩石圈发生了一定程度的减薄。随后,岩石圈—软流圈界面上移至地壳底部,使花岗质岩浆在地壳浅部处于较高的温度环境,岩浆缓慢冷却和充分分离结晶形成含石榴石花岗岩(~283Ma)。3、通过古生代花岗岩类Hf同位素特征揭示地壳深部物质组成,限定中亚造山带南界塔里木北缘-南天山地区地壳深部物质组成主要以前寒武纪古老地壳为主,兼并含有少量新生地壳(如虎拉山地区)。虎拉山地区花岗岩类明显具有高和正的εHf(t)值(-8.68~+13.2)以及年轻的Hf模式年龄(543~1854 Ma),其以幸格尔断裂为界与塔里木克拉通北缘的库鲁克塔格地区(εHf(t)=-23.4~+2.5,TDM2=1244~2845 Ma)具有明显不同的地壳深部物质组成,因此,将幸格尔断裂认定为中亚造山带和塔里木克拉通的界线。4、结合前人研究成果,提出新的构造演化模式460~430 Ma南天山洋发生向南俯冲并产生了活动大陆边缘,并促使微陆块(如虎拉山地块)沿幸格尔断裂碰撞增生在塔里木克拉通;随后,430~370 Ma,产生新的弧系统(塔里木克拉通+增生体),辉长岩、闪长岩和花岗岩体即为俯冲产物。370~320 Ma,南天山洋向南俯冲终止,为单一的北向俯冲,并发生陆陆碰撞。320~270 Ma,本次研究的晚期花岗质侵入体以及南天山西段的花岗质侵入体形成于古南天山洋最终闭合之后的后碰撞环境中,并且岩体年龄呈现从东到西逐渐减小的趋势,暗示剪刀式闭合方式。
[Abstract]:The northern Tarim South Tianshan area is located in the Tarim Craton and the Central Asian orogenic belt, and the tectonic position is very critical. However, there are still disputes on the key problems of the South Tianshan ocean subduction polarity, the closed age and the deep crust material composition. This paper is a study of some Paleozoic intrusions in the northern Tarim North Shandong region. On the basis of detailed field geological survey, taking petrography, mineralogy, petrography, geochemistry and zircon U-Pb age and Hf isotopes as the main research means, a comprehensive study of rock formation, tectonic evolution and deep crustal mass composition has been carried out to obtain the following understanding: 1, the Paleozoic rocks of the northern Tarim North edge of the South Tianshan area were preliminarily determined. According to the statistical analysis of the newly acquired zircon U-Pb age and previous research results, the Palaeozoic magmatic activity mainly acts in the late Ordovician, middle Silurian to Middle Devonian and Late Carboniferous to Middle Permian, of which the late Ordovician magmatic activity is relatively weak and the intrusive body is smaller, and middle Silurian - middle three. Devonian (peak age 420 Ma) and Late Carboniferous to Middle Permian (peak age 284 Ma) have relatively large scale of magmatism, mainly granitic intrusive rocks, which constitute the main.2 of Paleozoic magmatism in the northern margin of Tarim and South Tianshan area, and discussed the origin and tectonic setting of the Paleozoic intrusive rocks in the eastern part of the northern Tarim South Tianshan region. The Middle Paleozoic rock types include gabbro, diorite and granite. The age of gabbro is formed from late Silurian to early Devonian (424 + 4 Ma and 416 + 4 Ma), with relatively high MgO and Mg# value (49-53), and positive epsilon (T) value (+4.0~+11.4), enriching large ion stone elements and losing high field strength elements, suggesting that the mother magma originated from the subduction plate. The depleted mantle wedge partially melted by the slice fluid, and the diorite intrusive age was early Devonian (415 + 2Ma), with the geochemical characteristics of the gabbro and the positive epsilon Hf (T) value (+3.0~+9.4), indicating that it originated from the separation and crystallization of the basaltic magma from the depleted mantle, and the granite body formed from the early Devonian to the Middle Devonian (408~385Ma). All of them belong to high potassium calcium alkaline weakly peraluminous I type granite, which are mainly derived from young material or mixture of new and old materials. Different types of rocks show geochemical characteristics similar to the Andean continental arc rocks in the region, indicating that the northern margin of the Palaeozoic was the active continental margin in the middle Paleozoic. The late Cenozoic rock mass is mainly granitic rock mass. The genetic type of the rock mass is characterized by A type and I type and S type granite. The kurchu II granite body (311 + 4 Ma) has the characteristics of A type granite, which is obviously different from the granite formed on the subduction zone, indicating its formation in the post collision environment. From the time point of view, from the kurchu II rock. Body, seven late intrusive bodies to the blind Suzhou pluton (311~302Ma), the formation depth of the source region is increasing (e.g., Sr from 91.9 to 192.8 to 592.5ppm), and the crust gradually thickens. After that, the granite (300~290 Ma) has the characteristics of low Sr (58.6~67.4ppm) and high Y (15.9~19.4ppm), suggesting the occurrence of delamination in the post collision stage, and the lithosphere occurred. A certain degree of thinning. Then, the lithosphere - asthenosphere interface is moved to the bottom of the crust, and the granitic magma is in a high temperature environment in the shallow crust of the crust. The magma slowly cooled and fully separated and crystallized to form a garnet granite (~283Ma).3. Through the Hf isotopic characteristics of the Palaeozoic granitoids, the deep crustal composition was revealed and limited. The main crustal crust in the northern margin of Tarim south of the southern orogenic belt of the Central Asian orogenic belt is the main crustal crust of the former Cambrian, with a small amount of new crust (such as the hula mountain area). The granitoids in the mountain area of the hiraman area have obvious high and positive epsilon Hf (T) values (-8.68~+13.2) and the young Hf model age (543~1854 Ma). The fault is divided into the kuukatg area (Hf (T) =-23.4~+2.5, TDM2=1244~2845 Ma) in the northern margin of the Tarim craton, which has a distinct crust deep material composition. Therefore, the luckel fault is identified as the boundary between the Central Asian orogenic belt and the Tarim craton.4, and a new tectonic evolution model, 460~430 Ma south, is proposed in combination with the former research results. The Tianshan ocean dives southward and produces the active continental margin, and causes the micro block (such as the hula Mountain Block) to proliferate along the Tarim craton, and then the 430~370 Ma produces a new arc system (the Tarim cratonic + hyperplastic body), the gabbro, diorite and granite body is the subduction product.370~320 Ma, and the South Tianshan ocean direction The southern subduction is terminated by a single North subduction and a continental collision.320~270 Ma. The late granitic intrusive body and the granitic intrusive body of the South Tianshan Shanxi section were formed in the post collision environment after the final closure of the ancient South Tianshan ocean, and the age of the rock mass decreased gradually from east to West, suggesting the scissors closure. Way.

【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P588.12;P542
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本文编号：1833616