The Deep Resistivity Structure of Southwestern Turkey: Tectonic Implications

Abstract

Magnetotelluric data along two profiles, across the Lycian nappes and the Beydag autochthon of the southwestern Taurides in the eastern Mediterranean region images shallow and deep crustal structures. Inversion of the magnetotelluric data from profiles K and H reveals two subzones of the crust of varying thickness; the first is the conductive and viscoelastic lower crust (< 75 ohm m), whereas the second is the resistive (500-7500 ohm m) and brittle upper crust. The thickness of the uppermost conductive units, the Lycian nappes, is found to be 3.5-4 km in the northwest and 0.5 km in the southeast. The total thickness of the autochthon that forms the resistive upper crust varies from 7-16 km beneath the Lycian nappes to 11-20 km beneath the Korkuteli region along profile K. The depth to the upper/lower crust boundary varies from 10 to 30 km in the region. The resistive upper crust is interrupted by more conductive vertical zones. One of these zones along profile K coincides with the Fethiye Burdur fault zone (FBFZ), one of the most prominent geological structures in the region. The FBFZ lies in continuity with the Pliny and the Strabo subduction zones in the Mediterranean Sea. Projections of all the vertical resistivity discontinuities in the MT images onto the gravity map with the main surface faults show an alignment parallel to the FBFZ, and the Pliny and the Strabo trenches. The Bouguer gravity map shows a low gravity zone between the towns of Fethiye and Burdur. This gravity low also coincides with the alignment of projections of vertical high conductivity zones onto the map. Almost no earthquakes occur in the conductive lower crust, whereas significant earthquakes occur in the resistive upper crust, and the resistive lithospheric upper mantle (~250 ohm m) in the southeastern part of the region along the profile K. In contrast, in the northwestern part of the profile, the upper mantle is conductive (80 ohm m), indicating a viscoelastic character.