【作者】 孙云锴；

【导师】 毛晓冬；

【作者基本信息】 成都理工大学 ， 矿物学、岩石学、矿床学， 2010， 硕士

【摘要】 变质岩是地壳的重要组成部分之一,占地壳总体积的近三分之一。研究区域变质岩石,可以获取该区域深部地壳演化的相关信息,还有利于发现其中丰富的矿产资源。变质岩石和变质地质作用已成为当今地质学家十分关注的研究课题,也是前寒武纪地质和探索地壳早期演化的重要内容,同时已成为近年来地质学领域内发展较快的学科之一。青藏高原是当今世界上海拨最高、面积最大、形成年龄最年轻的高原。西藏冈底斯造山带位于雅鲁藏布江结合带和班公湖—怒江结合带之间,向西与克什米尔-拉达克岩浆弧地块相接,向东延伸至滇西腾冲陆块。研究区内构造运动频繁,变质岩分布广泛。本文立足于新一轮青藏高原1:25万区域地质调查的大量成果和数据之上,系统消化吸收并整合相关资料;依据古特提斯洋、新特提斯洋所经历的闭合碰撞造山作用,以及造山期后的高原隆升过程中所发生的一系列变质地质作用,自北向南依次将冈底斯造山带划分为班公湖-怒江变质带、革吉-班戈-洛隆变质带、隆格尔-工布江达变质带、冈底斯-察隅变质带、雅鲁藏布—南迦巴瓦变质带共五条变质带;在系统分析冈底斯造山带内五条变质带的变质岩石类型、出现的变质矿物组合,以及前人对这些变质岩石的岩石地球化学分析数据的系统分析基础上,在研究区内划分出八种不同变质强度的变质相类型:次绿片岩相、低绿片岩相、高绿片岩相、低角闪岩相、高角闪岩相、蓝片岩相、麻粒岩相和高压-超高压榴辉岩相。系统总结了各变质带中变质岩的地质特征、变质矿物组合、变质作用类型、变质作用事件及不同变质岩石的P-T条件;在前人的相关研究成果基础上,聚焦于各变质带中特征的变质矿物组合特征,在各变质带中分别划分出葡萄石—绿纤石带、绢云母—绿泥石带、黑云母带、铁铝榴石带、透辉石带、十字石—蓝晶石带、红柱石—堇青石带、蓝闪石带、矽线石带等特征的变质矿物带。基于上述研究,本文较系统总结了冈底斯造山带变质岩区的主要变质地质作用特点:1.变质岩和变质作用类型的多样性:冈底斯造山带的变质岩分布广泛,类型复杂,大体可分为七种岩石类型;变质作用类型齐全:区域变质作用、接触变质作用和动力变质作用均有出现,其中以区域变质作用为甚。2.区域变质作用的多期性:区域变质作用的变质时代具有明显的多期性,大体可划分为前泛非期、泛非期、加里东期、华力西期、印支期、燕山期、喜马拉雅期等7期,其中前泛非期、泛非期、燕山期和喜马拉雅期为研究区内主要变质时期;不同时期的变质作用在空间上多有叠加。3.变质地质作用过程的旋回性:冈底斯造山带内的变质作用受控于区内经历的复杂而多期构造旋回,其中新特提斯大洋板块构造演化的燕山晚期—喜马拉雅期变质旋回记录最为完整。此旋回清晰地展示了一套从海底埋深变质作用开始,经历洋壳俯冲高压埋深变质作用、陆缘和岛弧低压区域动力热流变质作用、陆—陆碰撞区域低温动力变质作用、陆内汇聚中压区域动力热流变质作用,而终止于地壳大规模造山隆升的退变质作用的完整变质演化历程。4.变质程度的差异性:整个冈底斯造山带的变质程度的非均匀性,总体上呈“南多北少,东高西低”的规律。即南北以雅鲁藏布结合带为界,南部变质岩出露面积大于北部;东西以当雄—羊八井断裂为限,东部变质程度高于西部。本文在上述的相关研究成果基础上,初步较系统的归纳和总结出了一套能反映研究区变质岩分布、变质强度变化、变质时期的能客观表达研究区变质作用时空演化规律的编图原则和图示方案,编制完成了《青藏高原冈底斯造山带变质地质图》(1:150万),具有较好的可读性。本论文从冈底斯造山带变质岩和变质作用方面的大量实际材料,结合沉积建造、岩浆建造和同位素年代学等多方面的信息和资料的综合研究,将研究区划分出基底形成、特提斯大洋闭合碰撞、喜马拉雅造山三个主要大地构造演化阶段;并分别就三阶段构造演化时期的变质地质作用,开展了较细致的论述。其中变质基底在研究区主要由念青唐古拉岩群和聂荣岩群组成,变质程度已达到角闪岩相和麻粒岩相。极低变质作用发生的时代在792～950Ma,480～590Ma两个时段,分别代表了前泛非期和泛非期两套构造-热事件的变质年龄。古特提斯和新特提斯大洋的构造演化造就了研究区内两条巨大的结合带:班公湖—怒江结合带和雅鲁藏布结合带。自二叠纪末始至始新世末止,二者的形成、发展和消亡经历了一系列变形-变质作用,形成了大量变质强度不同的变质岩石,构成了整个冈底斯造山带变质地带和变质带的骨架;印度洋板块从白垩纪晚期开始向北的快速漂移,到中新世末期与欧亚大陆板块的陆—陆碰撞,导致雅鲁藏布江洋的最后关闭,形成了一系列的逆冲推覆带,自此整个冈底斯造山带北西西—南东东向的地块展布格局基本定型;喜马拉雅地区地壳急剧增厚,同时也在该地区形成了一系列高压-超高压深成变质体。综上所述,本文初步总结了冈底斯造山带各变质带从发生、发展到最后形成这一过程的时空演化及相互之间的成因关系,对揭示变质地质作用对冈底斯造山带地壳形成演化过程的响应,以及在该区寻找与变质作用有关矿产资源具有积极的意义和有益的探索。更多还原

【Abstract】 Metamorphic rocks are an important part of the crust, crustal volume of nearly one-third.Researching regional metamorphism can acquire the information of evolution from rocky deep crustal, and thus found mineral resources which is rich in metamorphic rocks.Metamorphic rocks and metamorphic geological effect has become the focus of attention by geologists in recent years, and also is an important part for Precambrian geological and the early evolution of crust. So it is one of the fastest growing branch about geology in recent years.Qinghai-Tibet Plateau is the highest、largest and youngest plateau in the world. The Gandise orogenic zone in Tibet, westward joining Keshimier arc massif and eastward extending to Tengchong landmass in West Yunnan, is located between the Brahmaputra suture and the Ban-gong-Co-Nujiang suture. There are frequently tectogenesis and widespread metamorphic rocks in this area. This paper integrate relevant datum which is based on the data and results form 1:250000 regional geological survey of qinghai-tibet plateau. We divided Gandise orogenic zone into 5 metamorphie zones from north to south, they are Ban-gong-Co-Nujiang zone,Geji-Bango-Lolong zone, Ronger-Gongbujande zone, Gandise-Chai zone, Brahmaputra-Nanjabarwa zone. We analyzed the type of metamorphic rocks, metamorphic mineral association, geochemistry data from previous research achievements, so differentiated 8 metamorphic facies in Gandise. They are very low Greenschist facies, low Greenschist facies, high Greenschist facies, low Amphibolite facies, high Amphibolite facies, Blueschist facies, Granulite facies and Eclogite facies with high pressure. Geological characteristics of metamorphosed rock, metamorphic mineral association, metamorphism, metamorphic event and P-T condition with different metamorphosed rock in each zone are collected. We are focus on the metamorphic mineral association in each zone, and mark off prehnite-pumpellyite belt, sericite-chlorite belt, biotite belt, almandine belt, diopside belt, staurolite-kyanite belt, andalusite-Cordierite belt, glaucophane belt and Sillimanite belt from these zones.Based on the above research in this paper, it systematically summarizes the characteristics of metamorphism geological process in Gangdisi orogenic zone metamorphic rocks :1.The diversification of metamorphic rocks and metamorphism:metamorphic rocks with wide distribution in Gangdisi orogenic,type complex ,it can be roughly classified into seven types of rocks;Complete metamorphism:there are contact metamorphism、dynamic metamorphism and with regional metamorphism prominent.2. The multi-epoch of regional metamorphism: the metamorphic period of regional metamorphism has the obvious of multi-epoch, it can be roughly classified into sevent epochs. There are Caledonian、Variscan、Indo-Chinese epoch and with chief metamorphic period of former Pan-African epoch、Pan-African epoch、Yanshanian epoch and Himalayan epoch; Different periods of metamorphism superimposed in space.3.The cyclicity of metamorphism geological process:the metamorphism of metamorphism Gangdisi orogenic zone is controlled by the complex and multiphase structure cyclicity,there is complete metamorphism cyclicity record of of Late Yanshanian-Himalayan epoch in Neo-Tethys oceanic plate. This cyclicity clearly demonstrates a suit of complete metamorphic evolutionary process start from seabed buried depth metamorphism, experienced ocean crust high pressure subduction buried depth metamorphism、continental margin and arc low-pressure area dynami cheat flux metamorphism, ending at complete metamorphic evolutionary process of retreat metamorphism in earth’s crust extensive orogenic uplift.4. The difference in degree of metamorphism:the whole heterogeneity of degree of metamorphism in Gangdisi orogenic zone which generally displayed the rule of“largger Outcropped in south and smaller in north,highter in east and lower in weast”. That is to say, to the limit of the Yarlungzangbojiang suture in southnorth, the metamorphic rock outcrop area in south is larger than north; To the limit of the Yangba well- DangXiong breakage in eastweast,the degree of metamorphism in east in higher than west.In this paper, a set of principles of compilation and graphics program were established on the basis of the above-mentioned relevant research results,which can reflect the distribution of metamorphic rock, metamorphic grade, the tine of metamorphism and the law of Space-time evolution of metamorphism in the study area. The "Geological Map of Qinghai-Tibet Plateau Gangdise metamorphic belt" (1:150 million) was done and readable. Three main stages of tectonic evolution: Basement formation, Tethys Ocean closed, collision, Himalayan orogeny was recognized and the metamorphism of each stage was depicted particularly in the area based on the study about the metamorphosed rock and metamorphism of theGangdise zone applied sedimentary formation, magmatic formation and isotope chronology.In the study area, metamorphic basement mainly be composed of nyainqentanglha and Neirong group, whose metamorphic grade reached the amphibolite facies and granulite facies. The period of Basement metamorphism is 792 ~ 950Ma and 480 ~ 590Ma, corresponding the former Pan-African and Pan-African period of two structural - metamorphic thermal event ages.The tectonic evolution of Paleotethys and Neo-Tethys Ocean had created two zones: a great combination of two zones: Bangong-Nujiang suture and Yarlung Zangbo suture. From late Permian to the late Eocene, a series of deformation– metamorphism and formed a large number of metamorphic rocks of different metamorphic grade through both of suture formation, development and disappearance, which constituted the skeleton of metamorphic zone of the entire Gangdise orogenic zone. The Indian plate started rapid drift northward at the late Cretaceous, it occurred continent-continent collision with the Eurasian at late Miocene, leading to the final closure of the Brahmaputra Ocean, forming a series of thrust belt, and shaping the Gangdise belt‘s NWW - NEE framework. It rapid thickened of the crust, simultaneously, and formed a series of high pressure plutonic metamorphics in the Himalayan region.From the above, this paper summarizes the relationship between different metamorphic zone from origin to formed in Gandise Orogenic zone. These works are beneficial to open out the connection between metamorphism geological process and the crust of Gandise. And in the future, they are positive and helpful for mineral products prospection which is created by metamorphism in Gandise Orogenic zone.更多还原