Paleotectonic stress field and its evolution in central part of the intraplate yanshan orogenic belt during middle jurassic and early cretaceous: Constrains of stress inversion of fault slip vectorsEI北大核心CSCD

The Mesozoic structural deformation and sedimentation as well as the volcanism in the Chengde area, central part of intraplate Yanshan orogenic belt, have been systematically investigated in the last two decades. The paleostress fields leading to these complicated tectonic deformations remain unrevealed. Paleostress inversion of fault slip vectors, combining with the newly defined structural levels and the latest age dating results on the key lithostratigraphic units, is employed to establish the paleostress fields in the Chengde area during Middle Jurassic and Early Cretaceous. Three generations including five phases of paleostress fields have been identified in this study. The first generation is believed to be the Middle Jurassic NNW compression (D1) after the sedimentation of the Xiahuayuan Formation and previous to that of the Tiaojishan Formation volcanism (~173 Ma-165 Ma); The second generation includes two phases, the Late Jurassic and earliest Cretaceous N-S compression (D2-1) during and after the sedimentation of the Tuchengzi Formation(~152 Ma-139 Ma) followed by the NNE compression (D2-2) post to the Tuchengzi Formation and predate the Zhangjiakou Formation (~139 Ma-135 Ma). The third generation of paleostress field is inferred to be later than 125 Ma and characterized by a widespread multidirectional extension (D3-1) induced from vertical compression, followed by a leading and weak NW-NNW compression (D3-2). It is inferred that the contraction regime dominated in the Chengde area during the Middle Jurassic and the early Early Cretaceous, with the maximum principal stress axes (σ1) rotated ca 60° clockwise from NNW to NNE, and the sedimentation of the Tuchengzi Formation occurred in this compressive tectonic setting. Extension regime characterized the Early Cretaceous in the central Yanshan belt, even a weak compression once occurred during this period. There is no nearly W-E or NW-SE compressional stress field previously inferred as far-field response to the suspected subduction of paleo-Pacific Plate or Izanagi Plate have been identified in this area, which is likely resulted from intracratonic heterogeneous deformation or strain. ©, 2015, Science Press. All right reserved.