Structural Interactions Between Deep Mesozoic Strike-Slip Faults and Shallow Cenozoic Contractional Folds in the Northern Tianshan Foreland Basin (NW China)

In the rejuvenated mountain front, preexisting basement structures are often reactivated and interact with the subsequent thin-skinned deformation. How the deep structures affect the shallower ones is key to establishing the processes and mechanisms for the foreland fold-and-thrust system. We presented an exceptional case study on the structural inheritance between the deep Mesozoic strike-slip faults and the shallow Cenozoic contractional folds from the Northern Tianshan foreland basin, Northwest China, using high-resolution 2-D and 3-D seismic data. Based on the interpretation of seismic data and progressive restoration, our study illustrated the NW-trending Ai-Ka strike-slip faults controlled a dextral shear zone, which initiated the Gaoquan restraining bend in the basement during Jurassic. Later, these strike-slip structures, close to the mountain front, were reactivated during the N-S Mio-Pliocene contraction, and folded the upper décollements that characterized the localization of thin-skinned deformation. In contrast, in the further foreland, nonreactive strike-slip faults controlled basal décollement pinch-out, which localizes the thin-skinned deformation, resulting in en échelon folds that trace the strike of the deep strike-slip faults. The onset time of each anticline shows that the thin-skinned deformation first extended laterally and then propagated further north, resulting in ca. 7 km shortening along the whole foreland. Moreover, the shortening rate decreased eastward from 0.90 to 1.46 mm/yr along the Gaoquan-Kayindike structural line to 0.24–0.37 mm/yr along the Dunan structural line as the Sikeshu depression, constrained by the NW-trending Ai-Ka strike-slip fault, narrowed eastward. This feature implies that the width of the depression may control the amount of displacement propagation.