Electromagnetic Imaging of the Thrace Basin and Intra-Pontide Subduction Zone, Northwestern Turkey

Abstract

Magnetotelluric data were acquired at nine stations along an ˜80 km profile crossing the Thrace Basin and the Istranca Massif. These data were modeled using two-dimensional inverse techniques. The main findings are: (1) In the northernmost part of the profile, a wide (˜21 km) zone of the Istranca Massif with very high resistivity (>2000 ohm m) was imaged at a depth of 2.5 km, extending to ˜35 km depth. (2) Sedimentary rocks of the ˜63 km wide Thrace Basin (<75 ohm m) extend to a maximum depth of about 8 km along the profile. (3) Below the Thrace Basin, an undulating ˜10 km thick zone of conductive lower crust with low resistivity (<75 ohm m) is present. (4) The depth to the lithospheric upper mantle (˜250 ohm m) is about 45 km beneath the Istranca Massif in the northernmost part of the profile, and rises to a lowest value of 17 km toward the southeast part of the profile, possibly indicating mantle uplift. (5) The location and existence of the Intra-Pontide subduction zone in the Thrace Basin is the subject of debate. We imaged for the first time a slab subducting to the north beneath the Istranca massif in the Thrace Basin. (6) Our georesistivity model also indicates that, in contrast to western Turkey, an electrically conductive asthenosphere is not present in northwestern Turkey.