Characteristics And Geological Significance Of Guangping Nappe Structrue In Datian County, Fujian Province

Nappe structure of a certain scale exists extensively in Fujian province. Guangping nappe structure is located in the area of Guangping-Jian'ai and Taihua-Shangjing, in the north of Datian county, Fujian province. It is the most complete nappe structure with large area in Fujian province. It is 20 kilometers from north to south and 12 kilometers from east to west, covering an area of over 100 square kilometers.This paper carries out the theories and methods in structural geology, petrology, isotopic geochronology, mathematical modeling, statistic analysis, area balancing to study the characteristics of geometry, kinematics and chronology of Guangping nappe structure and to work out a preliminary dynamic model. We draw conclusions as follows:1. The allochthone marked by imbricate faults and the autochthone marked by folds of Guangping nappe structure are much different in characteristics of deformation from macroscopic to microcosmic. Located in Southwest Fujian nappe frontal belt, the study area is compressed intensively by the nappe structure, with undulating plane.2. A comparison between the Tangquan granodiorite and the granite porphyry proves it can be more significant to use the age of the granite porphyry to describe the characteristics of chronology of Guangping nappe structure than that of the Tangquan granodiorite. U-Pb dating of zircons from the granite porphyry gives an age of 142±1Ma, indicating the age for the formation of Guangping nappe structure.3. We used the area balancing method to calculate shortening estimates and analyze the errors of the incompetent coal-bearing stratum in the Tongziyan Formation belonging to autochthone. The result is 10.94±0.32% shortening.4. There is good similarity in petrology, lithogeochemistry, facieology and isotopic geochronology between the muscovite monzonitic granite in the study area and the Zhangfang granitoid in Shunchang area. The Zhangfang granitoid is likely to be the source of the autochthone of Guangping nappe structure. In this case, we found mathematical model on the problem of the source of the autochthone. In consideration of the affect of the left-lateral slip of the Zhenghe-Dabu fault, we draw a conclusion that the thrusting distance is between 55 to 105 kilometers, with a direction of N60W to N-S.5. Guangping nappe structure is the result of the subduction and the compression of the Izanagi plate underneath the Eurasian plate, with counter-clockwise rotation of the continent during Yanshanian.