The Structural Simulated Experiment To The Gravitational Sliding In The Northern Segment Of Longmen Mountain

Longmen Mountain tectonic zone is one of such important zones in southwestchina. It belongs to a part of the Yangzi plate according to the tectonic districts ofchina. Longmen Mountain tectonic zone is located in an approximately adjacent to thenorthwest edge of the Yangzi palte. It is in a position which is betweenSongpan-Ganzi tectonic zone and Sichuan basin. Huabei plate and Tibetan plate.From north to south, there are three main faults in Longmen Mountain tectonic zoneof which the main direction is northeast. These faults are: F1Pengguan-Anxian fault,F2Yingxiu-Beichuan fault and F3Maowen-Wenchuan fault. There are6geotectonicunits which are adjacent to Longmen Mountain tectonic zone, which are the ancientYangzi plate, the Chuanxi foreland basin, The Songpan-Ganzi folded zone, theMianlve-Qinling tectonic zone, The SanJiang tectonic zone and the Kangdian tectoniczone of which the main aligement is roughly from south to north.Longmen Mountain tectonic zone experienced different kinds of effects fromtectonic stress fields belongs to the ancient Yangzi plate, Huabei plate andSongpan-Ganzi plate in caledonian movement，Variscian movement，Indosinianmovement，Yanshan movement and Himalayan movement. It can be confirmed thatLongmen Mountain tectonic zone had been greatly transformed in the respect oftectonics. Therefore, it formed the features which are with their own specialty andwith the mutual connections in the respect of tectonic transformation.Longmen Mountain tectonic zone is also one of the important tectonicboundaries. Songpan-Ganzi folded zone is to its northwest, and Sichuan forelandbasin is to its Southeast. The formation of Longmen Mountain tectonic zone isexperienced very complicated process in the tectonic dynamics. There also are very complicates structural compositions and the great transformation based on thestructures which were formed previously from the tectonic movement in later stage.Due to that, the characteristic of multiphasic congruence has been showcased inLongmen Mountain tectonic zone. This thesis is based on the geotectonics, dependingon the tectonodynamics, the structural geometry and the science of sedimentary fromwhich the formation of Longmen Mountain tectonic zone is analysed and discussed.The main and important point of this thesis is the tectonic evolution and the mode of itin Indosinian movement, especially in the late stage of such epoch.The main structural grillage of Northern Segment of Longmen Mountain iscomposed by two parts which are the basement and the sedimentary cap. In the zone,the complicated lithological compositions can be detected. In different vertical andhorizontal positions of Longmen mountain tectonic zone, there are differentsedimentary faces existed such as the continental face, the oceanic face and paralicface. In Longemen mountain tectonic zone, there also are some planes ofunconformity which means this zone definitely experienced the different structuralmovements for many times in the geological history and was also greatly transformedby such movements.In the Northern Segment of Longmen Mountain tectonic zone, there are themultiple sliding systems which can be divided as3main section according the depth.They are the sliding system in deep level, the slding system in middle level and thesliding system in shallow level. In the epoch of Indosinian movement, the slidingsystem of middle made very deep and strong effect to the formation of the LongmenMountain tectonic zone.The main part of the Northern Segment of Longmen Mountain tectonic zone isformed by a series of secondary tectonic zones which are roughly parallel deckenstructures. The characteristic of overthrust and gravitational sliding is showed. Thereare also some exposed lithologic units in large scale and structure units in this zone,such as Jiaoziding complex and Tangwangzhai syncline. In this thesis, according tothe field work in Kuansghangliang which is in the Guangyuan and the indoorstructural-physics simulated experiment, some new academic points about theformation and tectonic evolution especially in the epoch of the earlier period of thelate stage of the Indosinian movement are obtained through the related analysis andforward simulations.The gravitational sliding is a kind of structural effect which can easily occurredunder the real geological conditions. When the rock mass is under the effect of gravity, the geopotential of it would be transformed to the form as the energy of motion of therock mass. In this process, the structural transformation will occur, and be kept as theform of the structural of gravitational sliding. According to the results of previousresearch, it can be recognized that if the related factors such as the rock property, thefluids which existed in the pores of the formations are considered in the analysis, therealistic angle for the occurrence of gravitational sliding is generally smaller than thetheoretical value.In the front sections of Longmen Mountain tectonic zone, kinds of structures aregenerally distributed under the partially extruding conditions. It includes the statureslike Spread drape fault, Turning drape fault, klippe and so on. Based on theconsequences of the previous research by other geologists, there is an area with highresistance which is a sign of the existed ancient faults system in the cohesive sectionbetween crust and mantle. The depth of this area is about20~100km under thesurface. Vertically, the direction of the upper half of this area is northwest, but thedirection of lower half of it is southeast. According to the mode of evolution of thetectonic zone under the condition of continuous overthrusting, the theoretic directionof this area should be consistent with the direction of the main faults of the Sichuanforeland basin which is northwest. So the real direction of the area with highresistance is difficult to be explained by the theory model of continuous effect ofoverthrust or overthrust of multiple phases. It means probably there should be anothermode of the evolution of the tectonic zone.There is a very strong and important connection between the gravitational slidingand the formation of the Northern Segment of Longmen Mountain tectonic zone.Simultaneously, the evolution of Longmen Mountain tectonic zone is highly related tothe formation of Sichuan foreland basin. Consequently, the vital point and mainessence of the research of gravitational sliding in this zone are the relationship of thecohesion of orogenic belt and basin.The structural simulation experiment is a very effective way in the research ofthe respect of tectonics. The essence of it is using different materials to establish themodel for simulating the tectonic process under the conditions of external force whichis produced by certain of equipment. From the observation towards to thetransformation of the layers of the model, the theories in tectonics can be tested andconfirmed.To the Longmen Mountain tectonic zone, in the early phase of early TriassicEpoch and the early and middle phase of middle Triassic Epoch during Indosinian movement, the tectonic background is stable passive continental margin, whichincludes the feixianguan formation, the jialingjiang formation and the leikoupoformation. After that, the Longmen Mountain tectonic zone probably experienced themovement of which the main characteristic is stretching. Such stretch is caused by thedistinctive upheaval of the blocks. The speed of upheaval of Songpan-Ganzi plateau isfaster than that of Sichuan basin, such a distinction caused the formation of rift zones.Under the conditions above, the area of high resistance mentioned previously wasformed. The period probably lasted from the end of middle Triassic Epoch to the earlyphase of late Triassic Epoch.Through the simulated experiment, it demonstrates that under the background ofdistinctive upheaval the possibility of the occurrence of the gravitational sliding isexisted. Such effect may cause the forming of extrusive tectonic environment in thefront edge of the sliding rock mass. Through the multiple analysis and the integrationof explorations which are finished by other geologists and the consequences ofprevious research, the evolving process of the Northern Segment of LongmenMountain tectonic zone since Indonesia movement can be divided into two sectionswhich are tensional environment caused by the distinctive upheaval in the early phaseof late Indonesia movement, and the overthrusting period which is after the first one.Based on such an evolution, the tectonic appearance of Longmen Mountain tectoniczone is formed.