A Study Of Electrical Structure Of Crust In Southeastern Qinghai-Tibet Plateau

Qinghai-Tibet Plateau is one of typical areas where collision of continental plates existing and the high terrain results from collision between the Eurasian Plate and the Indian Plate that are still colliding mutually at a certain rate.Therefore,QinghaiTibet Plateau is known as the natural laboratory of geodynamics and geology.Deep structure and state of materials especially in southeastern Tibet are key points of studying the dynamics of Qinghai-Tibet Plateau.This paper is based on SinoProbe-01 and we try to study the electrical structure of the crust and state of materials in crust by magnetotellurics profile data collected in southeastern Tibet.The data processing,2D inversion and 3D inversion are taken advantage to obtain the electrical structure,which shows a characteristic of vertical stratification.High resistance bodies of various sizes are distributed widely in upper crust.However,in mid-lower crust high conductor bodies of average 20 km thickness are generally distributed and the upper mantle is dominated by High resistance bodies.One thing is worth noting that high conductor bodies in midlower crust are not distributed continuously but partially,which means that connectivity among the high conductor bodies is poor.In addition, there is a clear high conductor strip crossing the faults near Jiasangka-Chibu Fault in 3D horizontal resistivity slice,whose headend has crossed the Bangong-NuRiver Fault.In the 2D inversion model,a low resistance path exists at a depth of 40 km beneath the high resistance body north of Bangong-Nu River Fault and the resistivity is just more than ten Ω.m.It is inferred that this one is the reflection of aforementioned high conductor strip and such a situation of distribution may be under the effect of thermal diffusion.In addition, high conductor bodies surrounded by high resistance bodies generally keep a state of extending from south to north in the east of Lhasa-Gangdise Block and the south end has arrived at Jiali Fault.The author holds the view that relatively weak materials exist beneath southeastern Tibet and these conductors may make the crust and the upper mantle not coupling powerfully.In result,the high conductivity regions may mean the decoupled regions.Besides,we haven’t made a conclusion as the previous magnetotelluric result that large-scale as well as banded lower crust flow exists in the study region.It is showed that those high conductor bodies of average 20 km thickness are just distributed partially and the connectivity among the high conductor bodies is poor,which means they may keep a state of plastic creepage.At the same time,the apparent trace of channel flow isn’t able to be found.This model may not be consistent with the continuous channel flow escaping to east.