Late Tertiary faults and their paleostress along the boundary between the Kuqa Basin and the Tianshan Mountains

Field investigation shows that the boundary between the Kuqa Basin and the Tianshan Mountains can be divided into two sections with the Yanbulak area as the di-viding point. In the western section, the Mesozoic strata overlie unconformably on the Paleozoic rocks. The ba-sin-dipping faults developed in both Mesozoic and Paleozoic rocks. The eastern section is characterized by basin-dipping normal faults separating the Paleozoic strata and Tertiary. The brittle structural analysis was carried out along the ba-sin-range boundary. 360 measurements of striations have been obtained at a total of 25 sites. Paleostress reconstruction indicates that the basin-range boundary was in an exten-sional condition, with some superimposed strike-slip, during the Late Tertiary. The extension could be explained by the vertical block uplift of the Tianshan Mountains.