Varying Indian crustal front in the southern Tibetan Plateau as revealed by magnetotelluric data

Abstract

In the southern Tibetan plateau, which is considered to be the ongoing India–Eurasia continental collision zone, tracing of the Indian crustal front beneath Tibet is still controversial. We conducted deep subsurface electrical modeling in southern Tibet and discuss the geometry of the front of the Indian crust. Three areas along the Yarlung-Zangbo river zone for which previous magnetotelluric (MT) data are available were inverted independently using a three-dimensional MT inversion algorithm ModEM. Electrical horizontal slices at different depths and north–south oriented cross sections at different longitudes were obtained to provide a geoelectrical perspective for deep processes beneath the Tethyan Himalaya and Lhasa terrane. Horizontal slices at depths greater than − 15 km show that the upper crust is covered with resistive layers. Below a depth of − 20 km, discontinuous conductive distributions are primarily concentrated north of the Yarlung-Zangbo sutures (YZS) and could be imaged from mid- to lower crust. The results show that the maximum depth to which the resistive layers extend is over − 20 km, while the mid- to lower crustal conductive zones extend to depths greater than − 50 km. The results indicate that the conductive region in the mid- to lower crust can be imaged primarily from the YZS to south of the Bangong-Nujiang sutures in western Tibet and to ~ 31°N in eastern Tibet. The northern front of the conductive zones appears as an irregular barrier to the Indian crust from west to east. We suggest that a relatively less conductive subsurface in the northern portion of the barrier indicates a relatively cold and strong crust and that the front of the Indian crust might be halted in the south of the barrier. We suggest that the Indian crustal front varies from west to east and has at least reached: ~ 33.5°N at ~ 80°E, ~ 31°N at ~ 85°E, and ~ 30.5°N at ~ 87°E and ~ 92°E.