Deep resistivity structure of the northwest Indian Himalaya and its tectonic implications

Abstract

Long period magnetotelluric (MT) data were collected at 15 stations on a 250 km long profile in the northwest Indian Himalaya to study the structure of this continent-continent collision zone. Two dimensional MT inversion was used to find a resistivity model that fit the data. In the upper crust low resistivity was imaged on the limbs of the Tso-Morari dome and may originate in serpentenization or zones of graphite. The Indus Tsangpo Suture was imaged as a sub-vertical conductive structure that dips northeast and merges with a mid-crustal conductor. A north dipping zone of low resistivity is imaged at the top of the underthrust Indian Plate and is likely due to fluids expelled from the underthrust sedimentary rocks. North of the Indus Suture zone this layer is located at 20-25 km depth with a conductance around 3000 S. The resistivity of 5-10 Ωm can be attributed to the presence of fluids, likely partial melt or aqueous fluids. This layer is underlain by a relatively resistive Indian crust that extends from the High Himalaya to north of the Indus suture. A decrease in deep resistivity was observed at the northern end of the profile, and is similar to the structures observed further east in the region of the indepth study, despite the smaller north-south extent of the orogen in the Indian Himalaya.