Detection of the deep crustal structure of the Qiangtang terrane using magnetotelluric imaging

Abstract

To determine the deep electrical structure of the Qiangtang terrane, northern Tibetan Plateau, we reanalysed three broadband magnetotelluric (MT) profiles collected by China University of Geosciences (Wuhan) in 1993–1994 and derived corresponding 2-D resistivity models. In these models, a remarkable high-conductivity layer that was divided into northern and southern parts and that had formed an antiformal zone of high conductivity beneath the central Qiangtang terrane was visible. This high-conductivity layer corresponds well with the trace of the southward subduction of the mélange from the Jinsha River suture inferred from surface geology. According to our resistivity models, the crust of the northern Qiangtang terrane is mostly composed of mélange. The underplated mélange may be closely related to the formation of the high-conductivity layer and provide a reasonable explanation for the cause of special geophysical features in this area. In addition, the similarity between these resistivity models provides evidence that the Qiangtang anticlinorium extends eastward to at least 92°E, whereas the differences between them may offer an explanation for the gradual narrowing of the metamorphic belt from west to east in the central Qiangtang terrane.