Late Triassic tectonic stress field of the southwestern Ordos Basin and its tectonic implications: Insights from finite-element numerical simulations

The tectonic stress field of the southwestern Ordos Basin during the Late Triassic is controversial. The major controversy is whether the southwest- ern Ordos Basin was a compressional basin throughout the Late Triassic or whether it transformed from an extensional into a compressional basin during this period. We divided the Late Triassic into the early to middle and late to terminal periods. Two paleotectonic stress field simulation models of the southwestern Ordos Basin were constructed using finite-element software (ANSYS 10). Our results showed high consistency with regional geologic correlations, suggesting the credibility of the models. We found that the southwestern Ordos Basin was dominated by NE-SW extensional stress and strain during the early to middle Late Triassic, associated with strike-slip faulting along the western margin of the Ordos block. This is consistent with the development of syndepositional normal faults and was probably induced by the scissor collision from east to west between the North China craton and Yangtze block. The tectonic stress field of the southwestern Ordos Basin during the late to terminal Late Triassic mainly manifested as NE-SW compressive stress and strain. The dominant tectonic dynamics for the Ordos block during this period may have changed to northward compression of the Songpan-Ganzi and Qiangtang terranes. The southwestern Ordos Basin was characterized by compressional deformation and northeastward migration of the depocenter. The southwestern Ordos Basin transformed from an extensional basin associated with strike-slip faulting during the early to middle Late Triassic into a compressional depression basin during the late to terminal Late Triassic.