Neotectonism In The China-mongolia Border Region Of Dongwuqi County Of Inner Mongolia

Dongwuqi County of Inner Mongolia, as China-mongolia border region, locates at the eastern edge of Inner Mongolia plateau. Since Cretaceous Period, the terrestrial lake basins developed widely. The lacustrine strata before pliocene have been studied sufficiently, while the research on the lake evolution since quaternary was unsubstantial. It is found that the quaternary deposits in the study area are continuous and integrated, lake terraces and volcanic tableland developed completely, during this field work. Lake terraces, volcanic tableland and terrace deposits record the characteristics of the new tectonics movements in the study area substantially.Based on the chronological research on the quaternary deposits and the interpretation of shallow-layer seismic profile, indoor remote sensing, explanation on topographic map and field survey, the study area can be divided into Chaobuleng uplift area in north and Zhunerren fault area in south. These two parts are bordered by the hidden active fracture in the north of Chaobuleng. According to previous date and field geology investigation, the hidden active faults in northern Chaobuleng formed in Paleozoic era, characterized in old fracture activation, and transformed from reverse fault to normal fault, in tectonic nature. Chaobuleng uplift area have developed three order lake terraces, approximately formed in middle Pleistocene between 250-310 ka respectively, which came from thermoluminescence age. Zhunerren fault area have developed five order lake terraces, formed from late Pleistocene to Holocene, between 21-8.6ka approximately, which came from thermoluminescence age. The whole study area have developed eight order lake terraces at least from the top to bottom, where the three order lake terraces in uplift area should be developed in the fault area, showing as buried terrace in the fault area. The reason for the division and distribution of terrace in the study area is that quaternary lake deposit was controlled by the hidden active faults in northern Chaobuleng.This article, through the research on the grain size analysis of lake deposit in different locations and terraces, (1) revealed that the evolutionary characteristics of Quaternary deposit from middle pleistocene alluvial lacustrine sedimentary to lakeshore sedimentary, from late Pleistocene shallow-lake sedimentary and Holocene lakeshore to alluvial lacustrine sedimentary;(2) reprduced the highest distribute location of the water surface of the basin in faulted area, corresponding to 930 meters contour line now; (3) reproduced the topography and geomorphology of some bottom of basin in Quaternary southern uplift area, revealed its characteristics in topography and geomorphology from the macroscopic angle -high in south and east, low in north and west, and it be controlled by the regional tilting movement from south and east to north and west;(4) constructed eight Quaternary basin filling sequences, recorded the evolution progress of Quaternary basin from formation to disppearance.According to the analysis of the actual-measured profile during field work and samples, previous date about age of basalt, the activity intensity of Cenozoic volcano is weak to some extent. The Cenozoic volcano shows central type explosive-effusive facies, caldera in geomorphology.On the basis of the research on the characteristics of lake terraces and fracture activity, and the characteristics of the Cenozoic volcanic rocks, the evolution of new tectonics movements in study area can be divided into four evolution stages mainly. Besides being impacted the regional tilting movement from south and east to north and west, the evolution of new tectonics movements in study area was mainly controlled by active fracture. Therefore, the secondary uplift, fault and tilting movement happened in the inner of quaternary basin. Based on research, the activation of hidden fracture in northern Chaobuleng commenced from middle Pleistocenem, which can be considered as the sign of the start of new tectonics movements in the study area. The evolution mechanism of new tectonics movements is the synthetic effect of the gravity isostasy and the subduction from Pacific Plate to Eurasian Plate.