Features Of Geological Structure For Xunyang-Shenhe Region, Southern Qinling Structural Belt

The formation of the Qinling orogeny belt.experienced an endless geological periodand it was the result of combined action between the North China plate and Yangtze plate. There are a lot of divergences about tectonic evolution and structural unit division of the Qinling orogeny belt.So the study will develop in the future.The research area lies in Xunyang basin which locating in the western portion of Wudang land mass and near Niushan land mass and Pingli land mass in the south and north . The research area located on the passive continental margin of the northern part of the Yangtze plate, belonging to Niushan-Diebu stratum zones. The structural position located in connection position among Jinjiling, the Southern Qining fold belt, a group of folds lies in south-east Liufengguan and north-east Baishui river-Baihe. By 2years field surveys for China Geological Surveys'1∶5 deposits exploration and collecting geological data about field surveys and indoor analysis and by studying of Structural features and their Spreading Regularity in space and time,we could describe the characteristics of geological structure in study area.The research area located on the passive continental margin of the northern part of the Yangtze plate,including transitional basement and sedimentary cover. The transitional basement includes metamorphic carbonate rocks of Yaolinghe group , Clastic Rock,,middle and basic volcanic rocks and Sedimentary Tuff in late Proterozoic Eras. The Sedimentary cover is constituted by the carbonate rocks in lower Cambrian-middle Devonian-Clastic Rock which overlies disconformably the lower the transitional basement.The strata in upper Sinian, late Proterozoic Eras and cambine system, Ordovician, Silurian ,early palaeozoic and Devonian ,late palaeozoic outcrop in In this area. The main strata are Sedimentary superficial metamorphic fine Clastic Rock with carbonate rocks . The deformation of Stratigraphic structure is stonger bu twith weak metamorphism.By getting the result of two years field survey and collecting occurrences and using the stereographic projection,then we determined the predominant mode of occurrence of folds in this area. The predominant mode of occurrence are 21°∠47°和185°∠38. The predominant mode of occurrence about faults are 21°∠47°和185°∠38°。The structural styles of early tension system were represented by detachment fault, bedding rhed fold,a-type lineation, sheath fold,Boudinage; The structural styles of extrusion were represented by regional consequent layer penetrative cleavage,ductile- shear features,regional thrust fault,asymmetrical lying fold. The overthrust faults in this area are Mapinghe fault,Lvhe fault and Shenhe fault. The structural styles of strike-slip system were represented by N-W to E-Wparallel displacement fault; The structural styles of extrusion syetem were represented by width folds,joints and kink; The structural styles of brittle extrusion system were represented by regional of the conjugate faults. Finally we determined the structure evolution sequence: E-W extension in Caledonian toVariscan; S-W extrusion and strike-slip in Indo-Chinese epoch; and S-N Shrinkage in Himalayan stage.According to the past research ,we divided the region geological structure development history into next four phases: tension system from early palaeozoic to Triassic basin; Strike-slip and thrust and nappe orogenic -extrusion syetem in Mesozoic; brittleness development from later Mesozoic to Cenozoic.