Numerical Simulation Study On The Present Stess-Deformation Mechanisms Of The Crustal Rock Mass Of "Lhasa-Linzhi Block"

"Lhasa-Linzhi block", located in the southeast of the Qinghai-Tibet Plateau which is in the joint of the Indian plate and Eurasian plate, belongs to the east tectonic knot of Himalayan tectonic belt. From north to sorth, the study region concerns three primary tectonic units, including the Gangdise-Nyainqentanglha block, the Yarlung Zangbo suture zone and the Himalayan Orogen. The regional geodynamic environment is extremely complex. The problems such as complex construction of the formation rock, geological structure, intense tectonic deformation, seismic ctivity with high intensity and high field stress are very acute. In the condition of this complex geological background, I will explore the present characteristics of regional tectonic stress-deformation field of Lhasa-Nyingchi block, reveal the mode action of stress-deformation of crustal rock mass in the region and analysis the dynamic mechanism of stress-deformation effect of the crustal rock mass, and all this studies are of great scientific value for researching and studying the problem of present intraplate tectonic activity in the Qinghai-Tibet block.This article has taken "the present stress-deformation mechanism of the crustal rock mass of Lhasa-Linzhi block" as study object. Through laborious field survey and indoor data processing, this paper has concluded and analyzed regional geodynamic environment、the characteristics of crustal rocks formation which is based on the extensive collection of previous studies and the results of the work, and made further study on the characteristics of the regional block inlay structure and fault structure activity. Combining the research date of regional seismicity activity and focal mechanism solutions, I would build the geology-mechanism model which could objectively reflect the crustal rock mass structure and dynamic source mechanism in the region and do in-depth numerical simulation study on the present characteristics of the regional stress-deformation field by using two-dimensional finite element numerical simulation methods. Thus, I will research the problems of the the maximum principal stress distribution、the three dimensional stress state of crustal rock mass and the stress concentration and variation of different land units, then discuss the control effect of crustal movement on the regional stress-deformation field characteristics, regional fault activity and seismic activity. The main achievements and understand of this paper include the following aspects:(1) The geological stricture in the research area are extremely complex and it mainly involves three primary tectonic units and six secondary tectonic units. The stratigraphic provinces in the research area belongs to Reservoir-Yunnan formation macrozone and includes three stratigraphic regions and six secondary stratigraphical subregion, thus there are many construction types of the formation rock, the magmatic rock and the metamorphic rock. The fault structures in the research area could be divided to three levels and are mainly in the EW-trending, meanwile there are the NE-trending, NW-trending and SN-trending fault structures.(2) The action direction of the regional maximum principal stress totally shows NNE direction, but in the effect of the regional deep fault and fault block movement, the main stess direction apparently changes in fault zone and its vicinity.(3) Under the regional stress field in NNE direction, the fault structures in different direction are at different traits. The EW-trending faults perform as strong reversal faulting, the left-lateral strike-slip activity of the NE-trending faults are very obvious; the NW-trending faults show the dextral strike-slip activity with significant peizotropy and the SN-trending faults have significant tensional characteristics.(4) Affected by the aboved dynamic source mechanism and the fault activity, the regional seismic activity mainly concentrate in three special tectonic positions, that is, the area along Yigong, Motuo to Chayu in the north and east of the high Himalayan Massif, the area along the shear-pull boundary belt in the western margin of the "Lhase-Linzhi block" and the area along Cuomei to Longzi in the North Himalayan tectonic blet.