PHYSICS OF THE EARTH AND PLANETARY INTERIORS, vol.125, pp.95-110, 2001 (SCI-Expanded)
The crustal structure of the northwestern Anatolia was studied by magnetotelluric measurements with periods up to 500 s at 20 locations along a line (line KS) crossed Istanbul, Sakarya and Bornova Zones to investigate deep electrical resistivity pattems that contribute to the understanding of tectonic setting of the region. The results obtained from the two-dimensional (2D) inversion of magnetotelluric data for the modes transverse electric (TE) and transverse magnetic (TM) show that the tectonic structure up to 5 km depth was comparatively complex and that the structural pattern was generally disturbed by the grabens and Neogene basins of low resistivity feature. The low resistivity (<80 m) zones stretched from the Istanbul Zone towards the northern part of the Sakarya Zone and from the southern border of the Bornova Zone towards the Gediz Graben in south characterize sedimentary sequences for this depth range. Based on the more detailed near-surface 2D geoelectrical model constructed using dc Schlumberger resistivity data the basin-fill deposits is about 1.5 km and 750 m thick in the Gediz and Gorede Grabens, respectively. Other smaller regions of low resistivity were also interpreted as the small-scale sedimentary Neogene basins within the Sakarya and Bornova Zones. Below about 5 km depth geoelectric models except a zone beneath Kazdag range show more resistive structure underlying these sediments. The resistive structure was correlated with the Precambrien crystalline rocks and gneiss schist basement of Sakarya and Bornova. Zones, respectively. A major zone with relatively conductive (similar to 10 Omega m) occurred within highly resistive mid crust beneath Kazdag range represents an electrically macro-anisotropic structure which could be followed from magnetotelluric sounding data in both TE and TM modes. It was discussed that the origin of this zone is associated with a coeval plutonism and metamorphism of latest Oligocene age, which yields a considerable low conductivity in the crystalline rocks. Of special interests was the zone of electrical conductivity, as it seems to exist a correlation between conductive structure and geotectonic features, which may support ideas about the high-grade metamorphism and accordingly north-south extending in the northwestern Anatolia. (C) 2001 Elsevier Science B.V. All rights reserved.