Electric Structure of Crust and Upper Mantle Beneath the Bangong‐Nujiang Suture in Tibet from Magnetotelluric Sounding

Abstract

AbstractBased on magnetotelluric (MT) sounding along the three profiles across the Bangong‐Nujiang suture in Tibet, we have established the electric model for this tectonic zone and adjacent areas and studied the features of the deep structure in this region. The result shows that there exist widespread discontinuous high‐resistivity bodies in upper crust along this zone and its both sides, which reflect spatial distribution of magmatic rocks that exhibits big difference between the northern and southern sides. Beneath the Gangdisê and Qiangtang terranes, middle and lower crust is characterized by extensive high‐conductivity layers, indicative of the sign of underthrusting of the India continent beneath Tibet. Below the high‐conductivity layers is a high‐resistivity block that emanates from the cold and rigid India crust diving northward. The electric structure model of the Qiangtang terrane can be divided into northern and southern parts. In the southern part, the high‐conductivity layer in crust is related with the impeding of the Bangong‐Nujiang tectonic zone to the underthrusting India plate. While in the northern part of Qiangtang, such zone is associated with the hindering of the Asian continent to the India plate as well as the southward subduction of the Asia continent. Because of the impeding of the Bangong‐Nujiang suture and Asian continent, the northward underthrust of India is likely not over the Bangong‐Nujiang suture, instead sinks into asthenosphere nearby the suture, causing upwelling of mantle materials that resulted in channels for exchanges of heat and materials in crust and mantle as well as large‐scale high‐conductivity bodies that extend downward to upper mantle. The electric structure of the Bangong‐Nujiang suture indicates that it is a set of steep and large faults cutting through the crust.