Study On Fault Stability Of Tamusu Area In Inner Mongolia

With the development of Chinese nuclear industry,the safe disposal of high-level radioactive waste has become unavoidable,even more prominent.At present,the best disposal method of high-level radioactive waste in the world is deep geological disposal.In the site selection of high-level radioactive waste disposal repository,the crustal stability in the preselected area is one of the important factors affecting the long-term safe operation of the repository.The stability of regional faults is very important to the preselected area of the disposal reservoir.Fault structures are well developed in the Tamusu area,and fault gouges are developed locally.In this paper,three faults?F₂-Tamusu fault;F₄-Wulantiebuke fault;F₇-Narenhala fault?were studied in the preselected area of Tamusu as the research object.Through field investigation,we use the mineral composition,chemical composition,carbon and oxygen isotope distribution and iron chemical distribution of fault gouges and wall rocks,quartz grain structure observation of fault gouge and the history of shallow seismic prospecting and earthquake and other methods to evaluate the stability of the preselected area.The study found that,?1?The surface characteristics of quartz grains in F₂ and F₇ fault gouges show that the activity frequency of F₂ and F₇ faults is relatively low since Holocene.F₂ and F₇ fault the latest activity is given priority to with“transition?”type.Fault activity is close to stick-slip.?2?Previous research results show that hydrothermal activities within faults may come from three aspects:deep hydrothermal fluid,low temperature hydrothermal fluid of wall rocks and atmospheric water.The activity of deep hydrothermal fluids is often related to active faults.The mineral composition and chemical composition of fault gouges and wall rocks are consistent.The main components of fault gouges and wall rocks of F₂ fault are quartz and feldspar.The wall rocks and faults of the F₄ fault contain a large amount of clay minerals and calcite,and the content of smectite in the fault gouge is significantly higher than that in the wall rocks of the fault.The wall rocks and gouges of the F₇ fault are mainly clay minerals such as quartz,feldspar and chlorite,illite and smectite.Active elements such as Ca in fault gouge are higher than those in wall rocks.The distribution of ¹³C and ¹⁸O in fault gouges and wall rocks of the three faults indicates that the fluid in the fault zone mainly comes from sedimentary water of marine strata and a small amount of atmospheric precipitation,and non-fault activities communicate with deep thermal fluids.It is worth noting that the carbonate hydrothermal processes in the fault zone may be related to the increase of the geothermal gradient in the basin.?3?There are differences in iron species,carbon and oxygen isotope distribution between the fault gouges and wall rocks of the three faults.The wall rock and gouge of F₂fault only contain oxidizing iron,indicating that the fault zone is under strong oxidizing condition.Compared with the fault wall rock,F₄ fault gouge contains a small amount of oxidized iron.The distribution of oxidized iron and reduced iron in the wall rock and gouge of F₇ fault is similar.?4?According to the shallow seismic exploration results in the study area,the quaternary strata have not been cut through by all the faults in the area,and most of the faults have a small dislocation distance.The frequency and magnitude of earthquakes in the area are small,and they are distributed outside the preselected areas with little influence on the preselected areas.Based on the characteristics of the fault gouges and wall rocks of the three faults,the tectonic characteristics and the earthquake history of the preselected area,the crust of the preselected area of Tamusu is in a relatively stable state.