| Based on the national key project for basic research on Tibetan plateau (G1998040800) and the 1:50000 regional geological survey project of Yuka and Liuliangsan area ,a Neogene Sertenshan-Xitieshan Obligue -Trusting Fault of (SXOTF) is stuied in the Northern Qaidam Basin. SXOTF is recognized in the Northern Qaidam based on the analysis of structures of area.This oblique trusting fault zone with northwestern-southeastern trending consists of Fault gouge,fault breccia and fault cleavage. Fault hanging wall consists of Sertengshan-Xitieshan napple, which is distribution in dextral en echelon. Fault footwall consists of Youcangshan Formation in Neogene. This paper emphasize the research of geometry, kinematics, age of formation of oblique-thrustin. It is discussed that geological significance of obligue -trusting.(1) This paper classified the strata of Sertengshan-Xitieshan in northern Qaidam basin into Daken-dabanyan group in Lower Proterozoic, Tanjianshan group in Ordovician-Silurian period, Aimunike group in Upper Devonian period and Guokesan formation of Zhongwu-nunsan group in Permo-Carboniferous. The strata of the region are divided into two structural layers: the basement rock consisting of metamorphic rock and cover layer of Mesozoic and Neozoic sedimentary rock..(2) The geometry of left oblique-thrust fault zone of Sertengshan-Xitieshan in northern Qaidam basin was studied systemically. According to the spread of nappe and relation between the nappe and depression, Oblique-thrust fault zone was divided into three parts in this paper: Sertengshan,Lvliangshan and Xitieshan.(3) According to macroscopic characteristics of fault zone, cleavage characters of fault zone, drag folds, the reverse "s" fold in the footwall, positive flower structures and small left strike-slip fault, the kinematics characters of fault zone of Sertengshan-Xitieshan are concluded: thrusting in section, left-slip fault in plane and the strike-slip displacement increasing from the west to the east. Thrusting is the main character, so it was named as left-slip oblique-thrusting fault.(4) Through the analysis on the spread of inner structure, thickness change of strata and seismic and geological data in the southern basin of Sertengshan-Xitieshan, this paper discussed the response of oblique-thrust effect on basin. There are coherent between the spread of oblique-thrusting structure, fold and fault structure. There were close relationships between oblique-thrust structure and the reverse "s" structure in the basin. Both of them are result of the left oblique-thrusting.(5) According to the study on seismicic data, sedimentary characteristics, contact relations, incision relation of the faults and strata related to the folds which are associated with the faults, this paper reached the conclusions: the oblique-thrusting structure of Sertengshan-Xitieshan in northern Qaidam basin was formed in middle Jurassic and the left-thrusting fault zone was established in the late Pliocene of Neogene. The formation of the nappe led to sinking of Qaidam massif, nappe thrusting basin depositing persistently and the sedimentary center changed.(6) The geological significance of oblique-thrusting fault of Sertengshan-Xitieshan was discussed in this paper. The oblique-thrusting effect of Sertengshan-Xitieshan is the result of the long distance effction of Himalayan orogenic belt intracontinent subducting, which is of great theory significance for studying regional structural framwork, relations between basins and mountains and oblique-thrusting effect of large-scale fault zone or orogen in northern Qaidam basin. Moreover, the result is of guidance significance for the forecast of combination gas, distributing and formation of nappe metal deposit in northern Qaidam basin. The study on the fault zone will promote the discussion of the rising mechanism of the Tibeteau Plateau.
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