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Lithospheric structure of the Arabia-Eurasia collision zone in eastern Anatolia: Magnetotelluric evidence for widespread weakening by fluids?

Eran Türkolu¹, Martyn Unsworth¹, lyas Çalar², Volkan Tuncer¹ and Ümit Avar²

¹ University of Alberta, Edmonton, Alberta T6G 2G7, Canada
² Istanbul Technical University, Maslak, Istanbul 34390, Turkey

Eastern Anatolia is the location of a young continent-continent collision between the Arabian and Eurasian plates. Long-period magnetotelluric data have been used to image the electrical resistivity of the crust and upper mantle in this region. The Anatolian block is being extruded to the west and is characterized by a low-resistivity (fluid rich) lower crust underlain by relatively normal upper mantle structure. The Anatolian Plateau has a lower crust that contains pockets of very low resistivity that may indicate local accumulations of melt. This is underlain by an upper mantle with an anomalously low resistivity that can be accounted for by an asthenosphere containing a few percent partial melt. The presence of fluids may weaken the crust and mantle sufficiently to permit lateral flow, and may also allow a decoupling of the upper and lower portions of the lithosphere. The lithospheric structure of the Anatolian Plateau is similar to that of the northern Tibetan Plateau, with zones of elevated fluid content. However, low resistivity in the Anatolian crust is found in isolated pockets, rather than the widespread regions observed in Tibet.

Key Words: continent-continent collision • plate tectonics • rheology • orogenesis