NEW CONSTRAINTS on THE TECTONIC HISTORY OF THE NW ANATOLIAN REGION: PALEOMAGNETIC RESULTS FROM MIDDLE EOCENE VOLCANIC UNITS AROUND THE ALMACýK BLOCK, TURKEY

We present new paleomagnetic results carried out on middle Eocene volcanic rocks at 25 sites in NW Anatolia, in order to better understand the regional tectonic deformation processes along the North Anatolian fault zone. The mean directions obtained from the Yýgýlca area in the Istanbul zone (D=191.5°, I=-47.1°, α₉₅=6.2°) indicate no tectonic rotation relative to the reference direction of the stable Eurasia (D=191.0°, I=-53.2°, α₉₅=5.0°). The paleomagnetic directions in the Almacýk block and the Armutlu region suggest CCW rotation of 21.5° ±7.8° and 14.8° ±14.5°, respectively, relative to Yýgýlca. These findings support the tectonic model, which has been previously suggested that both the Armutlu region and the Almacýk block were emplaced in the same area. Our paleomagnetic results indicate that through the right-lateral strike-slip movement of the northern branch of the NAF, both the Armutlu region and the Almacýk block were rotated in a counterclockwise sense with respect to the Yýgýlca area. In addition, within some parts of the block, an internal deformation with large declination anomalies ranging from 160° to 250° was observed in this and previous studies that could be explained as a result of chemical remagnetisation of hydrothermal events, stress-related magnetisation or small block rotations.