Differential deformation mechanism of E–W-trending Weiningbeishan fold-thrust belt from central Ningxia, NW China

Abstract

The Weiningbeishan fold-thrust belt (WFTB), located in the transitional zone of the Tibetan Plateau, Alxa Block and Ordos Basin, is an ancient intracontinental orogenic belt. In this article, structural analysis is conducted to more finely reveal differential deformation between the Devonian and Carboniferous strata in the WFTB. We found that the E–W-trending open folds are mainly developed in the Upper Devonian Zhongning Formation (D₃z), while the E–W-trending close and tight folds are mainly developed in the Carboniferous strata. The N–S minimum shortening strain of the bottom boundary of Member 2 of the Upper Devonian Zhongning Formation (D₃z²) is 21.1%, whereas the N–S minimum shortening strain of the bottom boundary of Member 2 of the Upper Carboniferous Danliangshan Formation (C₂d²) is 64.1%. We propose that the E–W-trending open folds in the Upper Devonian Zhongning Formation (D₃z) and E–W-trending close and tight folds in the Carboniferous strata were formed under the N–S compression during the Middle–Late Triassic. The Zhangyigou and Laoyagou faults are the main tear faults to accommodate differential displacement on the surface between the Upper Devonian Zhongning Formation (D₃z) in the east and Carboniferous strata in the middle, which change into a décollement fault in the deep part of the Dafosigou fold area in the middle to accommodate differential deformation between the deep Upper Devonian Zhongning Formation (D₃z) and Carboniferous strata. This study enables us to better understand the Mesozoic intracontinental deformation in response to far-field plate-boundary convergence in NW China.