Relation between electricity structure of the crust and deformation of crustal blocks on the northeastern margin of Qinghai-Tibet Plateau

Abstract

Study on the electricity structure along a magnetotelluric (MT) sounding profile on the northeastern margin of Qinghai-Tibet Plateau indicates that four crustal blocks can be de-termined from southwest to northeast, namely Bayan Har block (BH), Qin-Qi block (QQ), Hai-yuan block (HY) or the North-South seismotectonic belt and Ordos block (OD). The BH, QQ and OD blocks display a similar electricity structure of the crust. The upper crust represents a high- resistivity layer and the upper part of lower crust represents a low-resistivity layer with the resis-tivity increasing gradually with depth from the lower part of lower crust to the upper mantle. The electricity structure of the crust in these three blocks is similar to that in the complete blocks on the southern and eastern margins of the Qinghai-Tibet Plateau and belongs to normal electricity layering of the crust in slightly deformed or complete intracontinental blocks. The crust in HY block as a boundary zone has been significantly deformed, hence its electricity layering was de-stroyed and the structure was complex and the block became a recent tectonically active and great seismo-active region. The contact belts between the blocks on the northeastern margin of Qinghai-Tibet Plateau exhibit both upthrusting outward and strike-slip movement different from those on the southern and eastern margins of the plateau. The genesis of the low-resistivity layer in the crust is analyzed and the thickness of the lithosphere is estimated in the paper.