The Structure Characteristics And Tectonic Evolution In The Baiyinxile Area, Inner Mongolia

The study area is nearby the boundary of Geosyncline and plateform, lies in the epicontinental aggradational belt in the northern margin of the North China Plate, the structure is complex. Divergent views still exist as to the chronocorrelation of the Pre- Bainaimiao Group ,the majaor stratum of this area, the main reason is that the evidence of the Palaeobiological fossil and the appropriate age were not been found. Therefore, the author takes the Baiyixile area as his own research area. It is helpful to establish the strata-tectonic framework of work area and solve the chronochorizone of Bainaimiao Group through studying the structure characteristics and its evolution in this area.The research is mainly base on the field work, this paper analyzed the fold structure features of Baoerhantu Group and other structures in the area, and established the structure evolution history with the analysis of regional data, and also discussed the chronocorrelation of the Pre- Bainaimiao Group .The main comprehensions are as follow:1. The Baoerhantu Group has been undergone by several tectonizations. Based on the structural features. There are three types of the fold structure of Baoerhantu Group can be recognized: the rootless folding; NWW-SEE-face or near EW-face folds ; near S-N-face folds.2. Xuniwusu fault developed in area, whose fault tilting facing the south and is from pushing going against covering rushing structure, guessing its forming in late Jurassic.3. In the middle of the research area, the ductile shear zone was developed; it was possibly the identical structural system root belt with Xuniwusu fault, which belonged to the deeper tectonic level. Basic clod appears on this belt possibly represents the boundary of geosyncline and platform; it obtains the confirmation where the geophysics material results in.4. The Soft-sediment Deformational Structures exit in the first section of Baoerhantu Group, which had showed Baoerhantu Group formed in turbulent continental margin and the crustal uplifting and tesensional tectonic setting in the early time, possibly influenced by the seismic activity in the region.5. On the basis of the tectonic features, the tectonic evolution of the Baiyinxile region has been distinguished as the follow six stages: (1) epicontinental rifting and aggradational in the Preordovician; (2) the early fold structure deformation and the collision between the North China plate and the Siberia plate during the late Devonian to the late Permian; (3) the magmatic intrusion and the ductile shear zone forming during the early triassic to the middle Triassic; (4) the mail fold deformation and thrusting from the south to the during the late Triassic to the late Jurassic; (5) the later fold deformation during the late Jurassic to the early Cretaceous ;(6) the compression from southwest to northeast and the volcanic rock eruption during the middle Cretaceous to Neogene. In the Baiyinxile region, there may be an orogeny in the Mesozoic era, caused the lithosphere uplifting over 3.5km.6. The Pre-Bainaimiao Group consists of Bainaimiao Formation whose lithology is cupreous green-schists (amphibolite at the bottom is excluded), Xuniwusu Formation and Xibiehe Formation .The time is from early Cambrian to late Silurian. The third section to the fifth section of Pre-Bainaimiao Group should be setted on top of the Baiyunebo Group. The time of these three sections is from early Ordovician to early Silurian.