Abstract:

In the front of northern Dabashan thrust belt, there is a huge popup structure bounded by the NNEdipping Chengkou fault in the south, and the SSWdipping Gaoqiao fault in the north. The popup structure can be divided into several different segments along its strike, due to the variance of the occurrence characteristics and intensity of tectonic activity. To the northwest, it is a bidirectional thrusting structure and displays a positive flower structure; by contrast, the southeastern part is composed of a vertical Chengkou fault and a series of northdirected backthrusts, showing a semiflower structure. The 40Ar39Ar dating of syntectonic microthermal metamorphic sericite showed that Chengkou fault had an intense deformation during Yanshanian epoch (about 1433 Ma), causing rapid uplifting and thrusting of northern Dabashan thrust belt. During the propagation of this thrusting, a series of backthrusts formed because of the obstruction from the frontier of Dabashan thrust belt, and as a result, the popup structure was built up.

Key words: northern Dabashan, thrust belt: backthrust, popup structure, 40Ar39Ar age