Characteristics Of Nappe Tectonics And Analysis Of Chronology In Bengbu Fengyang

Bengbu uplift is located on the southern margin of the North China block, which is affected by Yanshan movement after the collision by South China block with North China block, recorded the inportant structural information. It’s worth studying on structure analysis.We noticed that a nearly EW thrust nappe structure situated in Bengbu-Fengyang area. In this study, we used several methods to research and investigate the thrust nappe structure’s geometry, kinematics and the formation age as well as the environment. By measuring, sampling and analysising the profile of the Mashan, Xiaohongshan and Xilushan overthrust structure, we concluded several consensuses:(1) The thrust nappe structure of Bengbu-Fengyang have a kinematics characteristic of the nappe from south to north; (2) Using software to analysis the stress state of researched area, we found that Fengyang area received compression between near SN and NW-SE two directions, this phenomenon consistent with the compression background analysis of the quartz grains vorticity;(3)According to the different deformation in two stages of nappe structure, two group representative foliation,182°∠10° and 142°∠33°respectively, and combine the age of quartz ESR dating in nappe structure,268.6±25.0-208.3±20.0Ma and 163.4±16.0-151.5±15.0Ma, we speculated that the thrust nappe structure experienced two stage:one is that the nappe get the total collision between North China block and Yangtze block near NB in Indosinian period;another is the collision between the Pacific plate and the Asian continental near NW in the early Yanshanian;(4) The Fengyang area overthrust structure formation temperature between 300 and 490℃ and relative pressure ranged from 0.29 to 0.63 GPa detected by hornbende-plagioclase geothermobarometer,two feldspar thermometer and phengite geobarometer respectively.Owing to Fengyang aea weathered seriously and rocks outcrop scarcely, researches were limited, many issues, such as nappe distance and the exact size yet to thoroughly understand. Further researches are needed to confirm these issues.