On The Metamorphism And Its Tectonic Significance In Gangdise Orogenic Zone Of Qinghai-Tibet Plateau

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.