Magnetotelluric Study of the Southern Pamir, Tajikistan

Abstract:

The Pamir region at the western prolongation of the Tibet-Himalaya orogen is a high plateau which accommodated the India-Asia collision by crustal shortening and thickening. The same east-west-trending orogenic belts, corresponding to continental terranes which amalgamated with Asia prior to the collision with India, wrap around the Pamir and Tibet. The southern Pamir is equivalent to the Lhasa terrane in Tibet and consists of Paleozoic-Mesozoic meta-sedimentary rocks, rare Proterozoic gneisses, and voluminous Creaceous-Palaeogene granitoids. The Pamir, however, has been displaced northward by approximately 600km with respect to the Tarim Basin. Today, there is strong geophysical evidence that a slab of Asian lithosphere has been underthrust south-southeastward beneath the Pamir.

In summer 2013 we installed 85 broad-band magnetotelluric (MT) stations in the southern Pamir covering a 200km wide and 100km long area between Murghab and Khorugh, with a site spacing of approximately 8km. MT data quality is excellent in the sparsely populated southeastern Pamir plateau and heterogeneous or even strongly disturbed by electromagnetic noise in the populated southwestern Pamir. The magnetotelluric survey was part of the interdisciplinary TIPTIMON (Tien-Shan-Pamir Monitoring Program) project.

3D inversion of the data reveals a prominent low-resistivity zone at a depth of approx. 10 km. This anomaly, with resistivities below 10 Ωm, extends across the entire southeastern Pamir and appears to be limited to the West by the Shakdara dome. The crystalline basement of the Shakdara dome is imaged as resistive material. We interpret the observed low resistivity of the southeastern Pamir is as partially molten felsic material at middle to lower crustal levels.