| Milin-Qushui section of Yarlung Zangbo suture belt belongs to the south Tibet valley in the southeastern Tibetan Plateau, which betweens the Nyainqentanglha Mountains and the Himalayas, and also is the eastern section of Zonal structure-Tethyan orogenic system(zone) that well-know in the world, it has a complex and unique lithospheric structure.The research section is in the famous Himalayan seismic belt, where the neotectonic activity is extremely strong and the seismic activity is frequently and strongly.This area has a steep topography and many types of geological formations, the Tectonic activities were strongly and the terrestrial heat is very obvious, especially the structural alteration is very prominent since the quaternary. The geological problems are very prominent, such as complex topography, geological formations (including Quaternary moraine), intense tectonic deformation, high-intensity, high geothermal and high temperature and pressure of ground water, high field stress etc., making the engineering geological conditions is extremely complex.This thesis conducted a study on the general characteristics of the structure-petrology in milin-qushui section of the suture belt, and discussed the different sections characteristics of the suture belt. In addition, made a study on the geological structure development characteristics and fault activity characteristics and analyzed its impact on the characteristics of the suture belt activities. The paper work is completed by the in-depth on-site geological research and room data analyze, and based on the comprehensive analysis of previous studies results. On the basis of geological studies and combined with the existing regional tectonic crustal stress test data and focal mechanism solution date, using the numerical simulation method to analysis the present stress-deformation characteristics in the four typical section (Milin, Langxian, Jiacha and Zedang) of the suture belt. Combined with the geological study and numerical simulation analysis results, making a in-depth analysis and discussion of the mechanical mechanism of the Yarlung Zangbo suture belt. The results of the analysis come to the following understanding:(1) The principal stress distribution is mainly the vertical gravity, horizontal tectonic stress is not a leading role in relative terms. Crustal rock mass stress mainly as the self-weight stress and the horizontal tectonic stress is comparatively small in the suture belt. It was presumed that the uplift of the Tibetan Plateau has reached the limit in present, and the three-dimensional stress state of the crustal rock is turning from "potential strike-slip" that dominated by the horizontal tectonic stress to the "potential normal stress fracture" which dominated by the gravitational field.(2) The suture belt has a subduction process on the transfer of crustal stress, making the powerful thrust which comes from the southern Indian plate decreased significantly after passing the suture belt. The suture belt also has a subduction process on the horizontal crustal displacement, the subtractive displacement and deformation mainly conversed into compressive deformation, fracture backward displacement or the extend-type dip-slip displacement along the fault zone.(3) The tectonic deformation characteristics of the west and east section of the suture belt is very different.In the northward pushing of the southern Himalayas block, the high Himalayas rigid block which in the east section of the suture belt make a northward subduction, and produce a strong push effect for the northern Gangdise-Nyainqentanglha mountain rigid block, having a very significant stress concentration near the south boundary fracture which is broaching contact.The north Himalayan plastic block which in the south side of the west section of suture belt make a northward obduction, pushing to the northern Gangdise Nyainqentanglha mountain rigid block, and mainly presented as a nearly north-south compression deformation, which difficultly to accumulate a high tectonic stress,therefore, there is no obvious stress concentration. |
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