Magnetotelluric investigation of the northern part of the Zagros orogenic belt

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The northern Zagros mountain belt is a young collisional zone where the European and Arabian plates collide. This regularly results in large, destructive earthquakes. Currently, two competing hypotheses proclaim different underthrusting processes of the Arabian plate below central Iran with and without slab detachment. Accordingly, the underlying tectonic models and their implications are poorly understood. However, numerical simulations of hypothetical electrical conductivity distributions derived from these studies show that MT is capable of distinguishing between these conflicting models. Our magnetotelluric (MT) investigation in the northern Zagros Mountains in NW Iran would thus contribute to the solution of a currently controversial issue.The observation of seismic anisotropy in NW Iran has been interpreted to depend on prominent geological features. Albeit, it is not clear whether these findings are related more strongly to mantle flow or stress in the lithosphere or a combination of both.The joint interpretation of the seismic and MT results will significantly enhance the understanding of the structure and tectonic evolution of the Zagros Mountains, especially by comparing it with previous MT studies in the southern part. Furthermore, the demonstration of the electrical anisotropy and the comparison with the seismic anisotropy will provide valuable information for the geophysical community as well as for the petrology and rheology in the area of measurement.The project comprises three 450 km long NE-SW profiles, which are about 30 km apart. Two long-periodic MT profiles with 5 stations each will provide information about conductivity structures in the deep lithosphere. The broadband MT profile with 23 stations crosses the main geological units and dissolves crustal structures in the upper lithosphere. The station setup is optimized with regard to the logistic effort and the subsequent 3D analysis.The data are processed using the Frankfurt software package FFMT. Indications of electrical anisotropy are obtained by evaluating the spatial distribution and frequency dependence of the complex apparent resistivity tensors and tipper vectors. The phase tensor (PT) has become an important tool for data visualization and interpretation because it is free of galvanic distortion. The transfer functions are modelled with ModEM, an inversion code for the calculation of isotropic 3D conductivity anomalies. The model resp. data fitting is then improved by an anisotropic 3D forward modelling code developed by the Frankfurt group with COMSOL Multiphysics®. The project includes the first interpretation of MT data in the northern Zagros Mountains. Our results will help to describe how the deformation has been accommodated in the northern Zagros collision zone and to compare it with that in older orogenies, thus providing new insights into the plate tectonic processes involved.