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The Analysis of Tectonic and Inversion of the Paleostress Field in the Zhangxian Salt Red Bed Basin in Northern Margin of West Qinling

The northern margin fault zone of western Qinling is one of the principal tectonic boundaries in the northeastern margin of the Tibet plateau. The Zhangxian red bed basin is an important part of the Northern fault zone of western Qinling. The study of the paleostress field on the basin is essential to understanding the tectonic evolution of the fault belt of western Qinling in the Mesozoic and Cenozoic periods. Our method is, first, to match the joints of same period according to the structure characteristics of the joint that are observed and measured in the field. Second, we inversed the paleostress field by using the stereographic projection method. The result shows that the study area has underwent four stages of compressive stress after the Cretaceous period, i.e., N-W, S-W, E-W and N-S compressive stresses. The inversion results of Palaeostress field shows that the area is dominated by strike-slipping tectonics after the Cretaceous sedimentation.