Tectonic Characteristic In The West Part Of Dingri-Gamba Basin, Tibet

The Dingri-Gamba basin, an important component of the world-famous Tethys-Himalayan tectonic zone, is located in the southwest part of Tibet. As a representative area of the international studies on continental collision and orogenesis, one of the best explorative prospect petroliferous basins in Tibet, it had experienced complicated deformation extremely. With the intense orogenesis influence, the basin suffered from intense reforming, which is related to the valuation of oil and gas resources directly. The structural deformation and reform of basin is the significant tectonic problem about petroleum geology and the oil-gas appraises in the Qinghai-Tibetan Plateau.In order to solve the tectonic problems existed in the Dingri-Gamba basin research, the thesis takes western part of the basin as priority study area on the basis of collecting and making use of prevenient research results, as well as accurate routes of geological investigation. Taking structural deformation analysis and new theories about petroleum geology as guide, detailed tectonic deformation analyses as method, the thesis begins with the geometry about present structures and tectonics, make use of the prevenient geophysical data, analyse the fundamental characteristics about base structure and the structure of overlying strata of the basin. Meanwhile, by taking the comprehensive tectonic analysis method concerning the geometry , kinematics and dynamics, this paper finds out various scale structural deformation pattern(fold, fault, joint, foliation and lineation etc.), and their current properties, scale, distrubution and combination rule, carrys out the study about deformation stages, component, geometrical pattern and mechanical properties ect. And the cover tectonic units were divided into several rational units. On the basis, contracting, extending, and srike-slipping are considered fully on the process of basin structural deformation. By distinguishing the structural sequences and deformation mechanism in different structural level, analyzing the effects of structural replacement and composition in different time, the structural deformation sequences and the structural patterns were built. And then the stress-field of the fold structures in the basin was ascertained after structural strain analysis. Finally, combined with the basin structural deformation , magma-volcano effection and the stratum characteristics, the author got the tectonic reform intensity, ascertained the areas which are propitious to gas-oil preservation in west part of the Dingri-Gamba basin, and provided scientific basis for gas-oil resources potential valuation and prospecting areas in Dingri-Gamba basin from the aspect of tectonic deformation and reform systematically.The paper mainly draws following several conclusions:1. Divided the research region into three first-grade structural units by analyzing the effects of structural deformation: northern thrust belt, central compound-fold belt, southern detachment structure belt, further, divided the northern thrust belt into nothern synclinorium belt and southern anticlinorium belt, central compound fold belt into northern synclinorium belt and southern anticlinorium belt.2. The study also suggested that the basin has experienced four tectonic reformations episodes since late Mesozoic to Cenozoic. The first is closed to tight folds result from middle to deep shearing mechanism along the delamination. The second is the thrust fault and fold structure caused by middle layer compression system. The third phase deformation is normal fault that developed along the formation interface from different times or the same stratum with different lithology in the basin. The fourth phase is that the NS graben structure was produced by EW expanding mechanism in late Cenozoic. Thereinto, the second deformation is the leading structural form in the basin, and the form of fold structure is fine and large, which is an advantageous trap structure.3. The study result about stress field of fold structure indicates that the deformation in basin is dominatingly trending NNE to near SN direction extrusion. The SN direction takes contracts strain, EW direction happens to extend, the fold motion axis stands straight. Therefore, the fold belongs to buckle fold.4. By the analysis of structural deformation intensity, the author think that the research area, Na jia-Xiong ru-Qa er wa-Qiang mu guo area and Ji long-Woma-E la-Bo er jie jia la area, is propitious to gas-oil preservation.