Late Paleozoic To Mesozoic Structural Deformation In Hexigten-Linxi Area, Inner Mongolia: Implication For Tectonic Evolution Of Xar Moron Suture

Hexigen-Linxi area is located in the eastern Inner Mongolia, where the Xar Moron suture developed. Late Paleozoic to Mesozoic strata and tectonic deformation structures as well as widespread plutonic rocks are well exposed in this region, which are thought to record the geological process from the closure of the Paleo-Asian Ocean to subduction of the Paleo-Pacific Plate beneath the Eurasian continent. In this study, geometric and kinematic analysis on folds developed within Late Paleozoic to Mesozoic strata were employed combining with chronological data from previous researches to identify the transformation and superimposed deformation from the tectonic Paleo-Asia system to paleo-Pacific system.in the eastern Inner Mongolia.NEE trending folds have been observed in Late Paleozoic strata. And the trending of folds within Late Paleozoic strata developed in the north side of Xar Moron Suture extended in direction of NEE-NE-NEE with varied scales undergone stronger deformation than the related strata in the south side of Xar Moron Suture and modified by later deformation. They are characterized by EW trending residual structures and some NW trending could be identified. The folds within Mesozoic strata dominated by kilometer-scale structures, are less complicated in geometry compare with those in late Paleozoic strata, They are dominated by NE trending to NNE trending in orientations. In addition to the analyses on fold deformation, paleostress inversion from fault slip vectors was conducted. At least four phases of contractional deformation and one phase of multidirectional extension have been defined. The first one(D1), which displays NNW-SSE compression, is related to the closure of paleo-Asian ocean and subsequent collisional event at the end of the Paleozoic to mid-Triassic; the second phase(D2),shows NE-SW compression and the source of their geodynamic are still unknown. the third phase(D3) indicates NW-SE compression, is resulted from the northwestward subduction of Paleo-Pacific plate during the mid-Jurassic to early Cretaceous; Since the early Cretaceous the research area likely developed a short-lived NWW-SEE shortening deformation. After early Cretaceous there may also existed a multidirectional extensional event.At present, the folds axis with S type in direction developed in the north side of Xar Moron suture appear to be modified by later structure deformation. NEE trending folds formed in early phase have been curved in direction by the NE-SW contraction, and formed a gigantic S structure in the north side of Xar Moron Suture, to the south, it likely because of the transcompressional force have been absorb by the shear of Xar Moron fault or the stability change of crystalline basement, which made this phase of compression didn’t formed curved folds in a relevant scale.