A comparison of the geological and geoelectrical structures in the Eastern Marmara region (NW Turkey)

摘要

Northwestern Anatolia contains different tectonic units which are presently bounded by the two branches of the North Anatolian Fault. The Pontide Zone in the north consists of the Istanbul-Zonguldak Unit to the west and the Ballidag-Kuere Unit (a remnant of Paleo-Tethyan ocean) in the east. The Sakarya Zone in the south is juxtaposed against the Pontide Zone due to the closure of Paleo-Tethys. The Armutlu-Ovacik Zone represents a tectonic mixture of both zones in the north and south. Neotectonic units, such as the Izmit-Sapanca Corridor and the Northern Sakarya Low, which developed south of the Istanbul Zone and north of the Sakarya Zone, respectively, represent an extensional tectonic regime. The relationship and continuations of these tectonic entities in the region were examined by a 90km-long, NW-SE trending magnetotelluric profile. Electrical resistivity is quite low (10 ohm m) beneath the Northern Sakarya Low and the Sakarya Zone at a depth of 26 km, compared to the northern areas. This low-resistivity zone may provide an indication of thinning in the total crustal thickness and a viscoelastic lower crust. Furthermore, in the northern part of the profile, the five-layered conductive sequence obtained by magnetotelluric modelling, may correspond to fragments of the Istanbul Zone and the Balhdag-Kure Unit underlying it.