Tibet Mangkam Geneva Fracture Deformation And Alteration Characteristics And The Impact Of The Project

Because of the western development strategy of the country,the Lancang River is also one of the important reserve energy bases for the transmission of electricity from west to east.The hydropower development conditions are good,the runoff is abundant and stable,and the sediment concentration of the river is small,and the cascade power generation benefit is huge.Therefore,relevant departments decided to deploy large-scale water conservancy projects in the Lancang River Basin to develop hydropower.The planned water conservancy project is located in the Sanjiang orogenic belt.The tectonic background is complex,with new structures,active structures,regional folds and faults.The project is only a few hundred meters away from the most recent regional rupture.Therefore,the deformation characteristics and activity of the fracture,and the alteration degree and alteration scope of the structural alteration rock near the fracture zone all play a decisive role in the site selection,planning and construction of the project.A total of eight outcrops of the fault were discovered in the study area.The outcrop of these faults is generally in the direction of South to East,which is roughly parallel to the flow direction of the Lancang river.The fracture surfaces are wavy and show obvious compressional characteristics.The fractured porphyry is widespread in the vicinity of the fault zone,and some obvious fault breccia is visible.The thickness of the gouge is between 0~10cm.Occasionally,the development of the scratch step indicates that the fault is thrust.No fault was found by visual observation,and the upper terrace and Quaternary sediments were cut.There are dozens of large and small Adit in this area.This paper mainly investigates six large adit.PDF202 and PDF23 fully reveal the RIA fault,which has a fracture bandwidth of about 25 m,and a large number of cleavage and structural lenses can be seen in the rock,and the main type of rock is mylonite.According to the degree of deformation,it can be divided into three bands.The weak deformation zone in the upper part of the fault is mainly based on the brittle deformation of ductile deformation,the strong deformation zone of the fault fracture zone,a lot of cleavage of rock,the structure of structural lens and the obvious rupture.The weak deformation zone of the footwall,a small amount of cleavage of the rock,and the structural lens are weakened,and the structural deformation is far away from the fault zone.There are 47 minor faults in the remaining cavern,most of which are fragmented rock and fault gouge.The ESR and quartz scanning electron microscopy dating of typical samples from field outcrops and cavern were carried out.The results of ESR show that the age of the fault is greater than 100 thousand years,and quartz SEM shows that the early Pleistocene and the former are mainly eroded quartz.All of these indicate that the fault has not been active since Late Quaternary.There are no new structural and active tectonic indications of overlying and adjacent quaternary disturbances,folds,faults and so on.There were no earthquakes along the fault zone and no hot springs were exposed.So the tile fracture is inactive.Through microscopic observation and laboratory tests of samples,it was found that the alteration rate of rocks near the broken zone in the Zhawa fault ranged from 15% to 18%,and the total amount of mineral components varied from 40% to 60%.The fault-affected zone alteration rate is 10% to 15%;the total mineral component variation is about 20% to 40%;and the intact new rock body is not affected by the fault,and the erosion variable(rate)is generally 5% to 10% of the rock.The total amount of mineral components is about 10%.It shows that the Ziwa fault has a large scale and a long extension.There is a certain alteration in the area,but it is mainly distributed along the fault zone,and the overall quality of the rock not affected by the fault structure is good.In summary,there are no obvious constraints to the construction of high dams in the project area.Only need to pay attention to avoid the strong deformation belt of Riwa fracture.