Abstract: The southern margin of Qinshui basin has mainly experienced three periods of tectonic activities since the Mesozoic: Indosinian, Yanshanian, Himalayan. Palaeotectonic stress field data have been obtained by analyzing the striation, buckle fold, and conjugated joint system in outcrop. In the east, the thrust compressing structure is evident within the NNE trending Taihangshan Fault Belt and the associated asymmetrical anticline shows 110° trending compression. In the central, the EW trending normal fault and graben system were probably produced by the SN trending compression in Indosinian and the subsequent tectonic inversion in the Cenozoic. The Cenozoic extension is very significant and the extension azimuth is 26° , 249° and 347° , respectively. The nearly SN striking faults composite the west boundary of the Qinshui basin, striation evidence of the nearly WE and the NEE-SWW trending extension has been gained and the extension azimuth is 94° and 72° . NNW-SSE, NW-SE, NE-SW, NEE-SWW and nearly SN striking conjugate joint systems exist in our study area. NW-SE trending horizontal compressive tectonic stress field of Yanshanian and NE-SW trending horizontal compressive tectonic stress field of Himalayan could be gained by the conjugated joints systems. The nearly EW trending horizontal compressive tectonic stress field was probably formed during the process of the conversion of the two main tectonic stress field.

Key words: Southern margin of Qinshui basin, Structural deformation, Tectonic stress field, Yanshanian, Himalayan