Tectonic Activity Of Tamusu Candidate Area In Alxa,Inner Mongolia

With the rapid development of nuclear power in China,a large amount of high-level radioactive waste has been produced.At present,deep geological disposal of high-level radioactive waste is recognized as one safe and effective way.Because of attractive properties of clay rock,e.g.very low permeability,high plasticity,strong self-sealing and adsorption,it has been proposed as one of the important candidate rocks for the geological disposal of high-level radioactive wastes.In recent years,the screening of clay rocks for geological disposal repository of high-level radioactive waste has been carried out in China.By now,the Tamusu site in Alxa,Inner Mongolia,is considered to be one of the favorable sites for geological disposal repository.In this paper,the activity of the Tamusu fault is investigated by using shallow seismic exploration,optically stimulated luminescence dating and iron element Mossbauer spectroscopy.The results indicated that Tamusu fault was relative inactive during the late Quaternary,1)The stratigraphic occurrence of the study area is relatively gentle and the geological conditions are relatively simple,so the shallow seismic exploration technology can be served as an effective way to reveal the thickness of underground strata and stratigraphic spatial distribution characteristics in the study area.The investigation shows that none of the Tamusu fault structures appeared in the Quaternary strata,indicating that the Tamusu faults were only active in the Cretaceous,and the tectonic activity of the faults has been weak since the Quaternary.2)A river terraced is analyzed by using satellite images,OSL dating techniques and differential GPS,the OSL dating results suggest that the terrace was formed at 56.8±5.2ka,the terraces are found with insignificant vertical displacement,although the terrace thread is discontinuous.Thus,it is thought that the Tamusu fault was relative stable since 56.8±5.2ka.3)The geochemical characteristics of fault gouge are closely related to its occurrence environment due to the activity of iron element chemical reaction and the extensiveness of crustal distribution,and there is a certain correlation between iron element chemical species and fault activity.The Mossbauer spectrum of iron elements collected from the fault gouge from the Tamusu fracture shows that the iron chemical species are all oxidizing iron,indicating that the environment in which the fault gouge is located is an oxidizing environment.And after a long period of precipitation forest filtration or exchange with the atmosphere,the reduced iron is completely replaced out,which further shows that the activity of the tower lignin fracture is weak.