The Late Triassic Structural Style And Later Stage Deformations From Jurassic To Cretaceous In The Liaodong Peninsula

Liaodong Peninsula,located at the eastern edge of the North China Block,and affected by the interaction of the Siberia Block,Paleo Pacific Plate,South China Block and the Eurasian Plate.Complicated structures were preserved within the Liaodong Peninsula,has always been the focus of tectonic research of the North China Block.However,the Indosinian orogeny produced by the collision between the North China and South China Block has been diluted and broken into pieces by following deformations,leading to weak understand of tectonics of the Liaodong Peninsula.In response to above scientific issue,regional structural analysis and geochronological dating were applied in two specific areas,i.e.,Pulandian area in the southern Liaodong Peninsula and Qingchengzi area in the northern Liaodong Peninsula.Methods of field geological investigation,structural geometric and kinematic analysis,paleo-stress recovery,and zircon U-Pb dating revealed the Later Triassic deformation(D1)and subsequent superimposed three episodes of D2,D3 and D4 in the Liaodong Peninsula.The D1 is characterized by NW-SE trending fold-thrust belt,near-surface brittle deformation,and kinematics of top-to-the NE thrusting.EBSD analysis for dolomite twins recovered principal compressive stress of NE-SW for D1 faults.Zircon U-Pb ages of syn-tectonic granite porphyry dikes and ⁴⁰Ar/³⁹Ar ages of metamorphic minerals constrained the D1 deformation at the Later Triassic.Thus D1 is part of the foreland fold-thrust belt of the Sulu orogenic belt produced by the continent-continent collision of the North China and South China Block.The D2 is characterized by NE-SW trending fold-thrust belt,indicating NW-SE compression tectonic stress field.Ages of the involved deformational strata and undeformed dykes intruded into the deformation constrained the time of D2 in the late Middle Jurassic-Late Jurassic.The Late Jurassic-early Early Cretaceous D3 is dominated by small-scale of SN trending and NW-SE trending strike-slip faults,which partitioned the Early-Middle Jurassic basins into isolate residual smaller basins,indicating tectonic switching from compression to extension.The D4 is characterized by large-scale of the middle-late Early Cretaceous extensional tectonics,including basins produced by local strike-slip faults,half graben basins dominated by normal faults,Liaonan metamporphic core complex and detachment faults.The D2-D4 are response of the subduction dynamics of the Paleo Pacific Plate,including high speed and low angle subduction,the changing of subduction direction from NW ward to NNW ward,and the low speed and high angle subduction related with the roll-back of the Paleo Pacific Plate,respectively.We therefore proposed a new tectonic model that the main tectonic framework was built by the Indosinian foreland fold-thrust belt,and was overlapped and superimposed by the subsequent of D2-D4 in the Liaodong Peninsula.