Metamorphic Petrology And Microstructure Features For Eastern Himalayan Syntaxis And Its Geologic Implications

Himalayan orogen is by far the youngest and largest active continent-continent collision belt in the world and is the ideal place for studying the plate dynamics of intracontinental convergence and investigating the mechanism responsible for uplift of the plateau. The western syntaxis in the vicinity of Nanga Parbat at the joint of India and Pakistan and the eastern syntaxis around Namche Barwa, Tibet are the two extreme points of Himalayas. They are the key places to understand the evolution of Himalayan structure and uplift of the Tibet plateau in that they are the most particular places in Himalayan orogen, which suffer the most remarkable metamorphism, deformation and partial melting, and also develop the fastest rate of uplift.High-pressure granulite and the coexisting eclogite and coesite-bearing ultrahigh-pressure eclogite have been subsequently found in the western syntaxis since 80s' last century. Geologists and geophysicists have carried out substantial work on petrology, geochemistry, chronology and geophysics, et al., which yields important reference material and constrains for explanations of questions, such as the delamination and exhumation mechanism for the lower crust, models of the rapid uplift of Himalayan orogen and deep subduction of India-Eurasia plate.While only a little has been done to study the eastern syntaxis at present. It is because, on the one hand, of the bad natural conditions in eastern Tibet, and on the other hand, that we are late in the study of this field. But eastern syntaxis has attracted peoples' eyes since Zhong Dalai et al. (1995) reported the finding of high-pressure granulite in this region and tends to become the focus and hot spot of study for geoscience circle at home and abroad.Indus-Tsangpo suture zone is the joint of Indian plate and Eurasia plate. The study on its evolution history can provide us dynamic evidence for continent-continent collision between Indian plate and Eurasia plate. Then what is the formation mechanism and deformation history for the Indus-Tsangpo suture zone? In addition, Tibet is characterized by great thickness, highly acidic and low Vp and Vs, but why does Tibet behave like such features? Since eclogite and the coexisting high-pressure granulite have been found in western syntaxis, we'll ask whether it is possible that eclogite also can occur in eastern syntaxis?The goals of the thesis are mainly to investigate the structural profile at Baila village in Indus-Tsangpo suture zone, and to provide us with effective reference information about deformation history of Indus-Tsangpo suture zone based on studies on petrology and petrofabric analysis of quartz in addition to detailed field observations. This profile lies near the Yalu Tsangpo river, by the road from Luxia to Baila village, Qiangna, Milin, Tibet. It belongs to the north of Indus-Tsangpo suture zone, and mainly contains mica-schist, quartz-schist and quartzite besides a few of marble and meta-basalt. Within the section, rocks are strongly deformed and develop fine schistosity. One group of lineations developed in most rocks' foliations is orthogonal to the strike, another group developed in others intersects with the strike at 40-60? The petrofabric of quartz for this section is classified into five types: The samples of Type I are east-west-striking and have orthorhombic symmetries with foliation (S) as the symmetry plane and lineation (L) as the secondary symmetry axis. The optical axis of quartz shows a great circle girdle perpendicular to lineation. This kind of petrofabric indicates that the rocks may form during the collision between Indian plate and Eurasia plate and suffer compression nearly along N-S direction; The samples of Type II are all nearly NNE-striking and have clinorhombic symmetries with lineation (L) as the secondary symmetry axis. This kind of petrofabric may be due to shearing and reflect that its formation may be at the same period as that of the NNE-striking shear zone (i.e. Yalu Tsangpo shear zone); The samples of TypeIII have triclinic symmet...