The Geometric Styles And Mechanism Of Mesozoic Deformations In The Southern Front Of The Micangshan, North Sichuan Province

Michangshan, located in the northeastern part of Sichuan province, is adjacent to the Qinling orogenic belt to the north and the Sichuan basin to the south, and is sandwiched between the Dabashan orogenic belt with northwestern trend and the Longmenshan orogenic belt with northeastern trend, on the east side and west side respectively. Because of its special tectonic location and become one of important areas for the study of the basin-mountain coupling relationship of the Sichuan Basin and Qinling orogenic belt. According to previous research work, overall, Micangshan is a anticlinoyinm,developed Pre-Cambrian basement in the fold core, the outcropped lithology is primarily Mesoproterozoic metamorphic rock, as well as magmatite(mainly acidic magmatic rock) which developed in it. Sedimentary covers from Sinian to Cretaceous is distributed around the core of the Micangshan anticlinoyinm, missing the sedimentary of the devonian and The carboniferous. Some supersequence set boundaries disconformities developed in the caprock indicates the uplift and subsidence of the crust in the area during the geologic history. A series of NW-trending and NE-trending thrust faults developed in the Micangshan area, which thrust to north along the northern border of the Micangshan and to south along the southern boundary. Some anticline and syncline folds near EW trending were developed in the caprock at the southern front of the Micangshan. However, the fold and fault developed in the east and west edge of Micangshan, were all reconstructed and superposed as the result of influence of Dabashan orogenic in the east and Longmenshan orogenic in the west. Although there are lots of previous research, there is still a great inadequate, particularly lacking the studying of the geometric styles and mechanism of Mesozoic deformations in the southern front of the Micangshan.The main research results are as follows: First, summarized in the geometric styles of basin-mountain zone, there are buried emergent thrust, monoclinal zone of the mountain front, tip line fold pair, backthrust and passive roof duplex, etc. Next, through the compilation of one structural outline and three tectonic sections, the structural framework of the southern Micangshan is established: Micangshan anticlinoyinm is a large-scale flexural folds which present as a box fold'geometric styles today, in the southern Micangshan, there has large buried thrust and passive roof duplex, and the forming mechanism of the steep dipping monocline in the mountain front are closely related with backthrust and buried emergent thrust. Then, according to the geometry of structural deformation with outcrop scale and the associated structure which reflect the kinematics and dynamics characteristics of the structural deformation, we consider that the mechanism of mesozoic deformations in the southern front of the Micangshan mainly include: flexural folding, fault-related folding, buried emergent thrusting, backthrusingt, kinking and superposition of folds. Finally, although we have the preliminary understanding on the structural framework,geometric styles and forming mechanism to the Micangshan, however, detailed study to the geometry and kinematic of the faults, in the southern front of the Micangshan, is still deficiency, which restrict the compilation of balanced geological cross-setions of Micangshan, and it is the key work of the future.