Late Paleozoic-Mesozoic Thrust System And Its Evolution In The Western Segment Of Daqingshan,Inner Mongolia

The Daqingshan thrust system in Inner Mongolia is located in the eastern part of the Yinshan intraplate orogenic belt along the north margin of North China Craton.Structural deformations since late Paleozoic in the Daqingshan belt bear important implications for a better understanding of the syn-collision tectonic deformation and subsequent intraplate tectonic deformation process.Previous studies mostly focus on the late Mesozoic large-scale thrust and nappe tectonics in the eastern segment of the Daqingshan thrust system,and subsequent metamorphic core complexes.The structural framework and geometric style of thrust system as well as the thrusting propagation sequence in the western part of the Daqingshan thrust system remain unclear.In this study,detailed mapping are employed to investigate the geometry and thrusting sequence in Tumod Left County and Tumod Right County,Inner Mongolia.A five-phase tectonic deformation process since late Paleozoic are established after clarifying the tectonic framework and the styles of thrust system.A couple of thrust styles are identified in the western segment of the Daqingshan thrust system.They are characterized by basement-involved type and capping-sliding type including triangle zone,the exposed and blind thrust imbricate fan,and duplex structures.Furthermore,all of three kinds of thrust fault-related folds are identified.The dominant thrusting sequence of the thrust faults during Middle and Late Jurassic is determined as the piggy-back propagation.During the Late Paleozoic-Mesozoic period,the study area experienced five stages of tectonic deformation.D₁:at the end of the Late Paleozoic,E-W trending thrust faults developed under S-N contraction.D₂:In Early Jurassic,E-W trending rifted basins developed under S-N extension.D₃:In mid-Jurassic-late Jurassic,E-W trending thrust faults developed under S-N contraction.D₄:In early Cretaceous,NE-SW trending thrusting fault developed under NW-SE contraction.D₅:In the early Cretaceous,NE-SW trending normal faults developed under NW-SE extension.The D1 is inferred to be related the final closure of the paleo-Asian ocean.The intraplate deformations in the study area are characterized by intervening contraction with extension.