Sedimentary Evidences Constrain On The Uplift Of The Micang Shan

As the northern boundary of Sichuan Basin, The Micang Shan locates in the north part of the upper Yangtze region, Which is the basin and mountain transition area among the Longmen Shan, Qinling orogen belt and Sichuan Basin, so it is important for researching the tectonic evolution and coupling relation of basin and mountain about Qinling and upper Yangtze region in Mesozoic. The uplift period of Micang Shan has large connection with spatio-temporal boundary of Sichuan Basin and tectonic evolutional framework.Based on the new research findings and progress of the south Qinling Orogenic belt and the Yangtze block in general, especially chose Jurassic sediment from both sides of the Micang Shan to study and contrast, then analyzed palaeogeographical topographic features and tectonic upwarping's feature of Jurassic Micang Shan. After concluding the research above, Uplift period of the Micang Shan was restricted and uplifting process was discussed, some pieces of conclusions and recognitions about the Micang Shan area were obtained as follows;1. Three cross sections were surveyed at Baishui, Ganchang and Pingxi to the south of Micang Shan, another cross section lied in Yankou to the north of Micang Shan, and column of lithology of Jurassic was made then. There were no remarkable discrepancies in sediment to both sides of Micang Shan from Early-Jurassic to early phase of Mid-Jurassic after comparing in detail. This research indicated that the Micang Shan uplifted later than early phase of Mid-Jurassic and the sedimentary environment was not separated until then. The northern boundary of Jurassic Sichuan Basin reached Xixiang area.2. Sichuan Jurassic Basin and the Qinling Orogenic Belt have been studied from the aspect of basin-orogen coupling after collecting new achievements of stratigraphy, petrology, structural geology and isotopic chronology about these areas. The Uplifting of Micang Shan was caused by the large-scale clockwise rotation of Sichuan terrane which started in middle-late Jurassic and restarted in Cretaceous.