Superimposed Deformation In The Kexueshan Area,the Western Periphery Of The Ordos Block

Kexueshan area in the western of Ordos block is characteristic of typical regional superimposed folds in Jurassic strata,documenting the main tectonic evolution progress since Mesozoic in the western periphery of Ordos block.The complex structural features and patterns of this study area may be related to its unique geotectonic location and complex tectonic deformation progress.All of which makes Kexueshan as an ideal place to research its tectonic deformation from Middle-Late Mesozoic to Cenozoic,the new views and research results as follows:On the basis of regional structural analysis,The teo-phase structural shortening deformation processes in this area were determined by field structural investigation.Meantime,the-phase tectonic stress fields related to the structural shorting deformation were reconstructed by using fault kinematic analysis in Kexueshan area,together with structural sieving.Synthesizing the regional structural analysis and geochronology,two stages of tectonic evolution were proposed since Late Mesozoic in Kexueshan area.During Middle-Late Jurassic?J₂-J₃?,under the control of NW-SE trending tectonic compression,the NW-SE structural shortening deformation occurs in Kexueshan area,which forms the NE-SW trending folds and thrust faults,and control the Middle-Late Jurassic deposition.This structural shortening deformation is likely liked with a combination of the southward convergence of the Siberian plate and the northwestward subduction of the Pacific plate.During Late Miocene-Late Pliocene?N₁²-N₂?,the tectonic stress field is transformed into NE-SW trending tectonic compression,resulting in the development of the NW-SE trending folds,which are superimposed on the early NE-SW trending folds,and featured by regional superposed folds.Representative superposed fold patterns are Conversion fold,T-shaped fold,Crescent fold,Tubular fold.Regional structure investigation shows that this structural shortening deformation coincides with the northeastward growth of Qinghai-Tibet Plateau.The above studies provide important evidence for the reconstruction of the intracontinental deformation process in the western periphery of Ordos block.