The Mesozoic Superimposed Fold And Its Tectonic Implications In Fuzhouwan?Liaodong Peninsula

As an important part of North China Craton,Liaodong Peninsula has experienced the contraction and extension of Mesozoic,and the Liaonan caprock's deformation is very strong and complex,which is rare in stable platform.It is of great significance to study the tectonic evolution history and geodynamic background of Liaodong Peninsula to understand the deformation in the Liaonan caprock.The deformation of caprock in southern Liaoning has attracted extensive attention of many geologists.Although the structural combination pattern and deformation process in this area have been deeply understood,the understanding of superimposed folds exposed and well preserved in Fuzhouwan area and their significance is not deep enough.In this paper,Mesozoic superimposed folds in the Fuzhouwan area in the south of Liaodong Peninsula are taken as the research object.Detailed field investigation and structural analysis are carried out along two nearly orthogonal sections.Fold elements such as stratigraphic occurrence and axial cleavage occurrence of superimposed folds in the Fuzhouwan are systematically measured and counted.Their superimposed patterns are analyzed,and the structural evolution sequence of folds is established.It is determined that the reverse junction of the late NE vertical horizontal fold is across the early NW anyan type fold.According to the general situation of the region,it is analyzed and judged that the sencond fold in this region are fault-related folds.Fold parameters are used to study concealed thrust faults.Relevant parameters of concealed thrust faults are calculated.The ramp dip angle of the thrust fault is 64.4°,the shortening rate of the hanging wall syncline is about 6.8%,the fault-parallel distance of the fault is 2.99 km,the displacement on the fault surface is 0.31 km,and the depth of the hidden thrust fault is 3.90 km.Based on the distribution of strata in the study area,it can be judged that the depth of the thrust fault is in the Cambrian systemBased on the comparison of regional geological relations and evolution,it is determined that the superimposed folds in Fuzhouwan are the result of the composite superimposed deformation of folds in Indosinian and early Yanshan periods.in the early stage,they were affected by the S-N compressive stress generated by the subduction of the Yangtze plate under the north China craton in Indosinian period,and in the later stage,they were affected by the NW-SW compressive stress generated by the NW subduction of the Pacific plate under Eurasia in early Yanshan period.Based on the structural analysis of the profile and previous research results,it is determined that the change of regional stress field in Fuzhouwan area is the result of the absence of Sinian sedimentary basement bulge on its east side,thus forming NW-trending echelon folds slightly different from EW-trending folds in Jinzhou area on the south side of the study area.Through the restoration of two periods of tectonic stress field,the regional tectonic evolution was reconstructed,and the tectonic evolution model of superimposed folds in Fuzhouwan was established.