Neotectonic deformation linking the east Anatolian and Karatas-Osmaniye intracontinental transform fault zones in the Gulf of Iskenderun, southern Turkey, deduced from paleomagnetic study of the Ceyhan-Osmaniye volcanics

Abstract

Left-lateral strike slip along the Dead Sea Fault Zone (DSFZ) between the African and Arabian plates is partitioned into a complex set of motions at its northern extension where Arabia impinges into the Anatolian collage. As a result, the nature of the contemporary link between the east Anatolian and Dead Sea transforms is unclear. To quantify strike slip motion expressed as tectonic rotations along the inferred southwest continuation of the East Anatolian Fault Zone (EAFZ), we have investigated the paleomagnetism of young (<1 Ma) volcanics in the Adana Basin-Gulf of Iskenderun region comprising the Ceyhan-Osmaniye volcanic suite. This volcanism is sited close to the intersection between the sinistral Karatas-Osmaniye Fault Zone (KOFZ) and the Neotethyian Suture. Nine sites from a basaltic lava field in the vicinity of Osmaniye are entirely of normal polarity and, in the context of their very young morphologies, are assigned to the Brunhes Chron; declinations are mostly clockwise from the present field. This age assignment identifies rapid Recent (<780 ka) uplift at the head of the Gulf of Iskenderun and is linked to a diversion of the Ceyhan river drainage and ongoing regional tilting. Eight sites yield a mean declination of 11.3 +/- 10degrees, implying clockwise block rotation on Riedel-type fractures on the northwest side of the KOFZ. Seven lavas sites from a volcanic succession near Botas, at the southwestern extension of the volcanic lineament are of reversed polarity and rotated counterclockwise by 43 +/- 7degrees with respect to the present field. Polarity, K-Ar, and morphological evidence indicate an assignment toward the latter part of the Matuyama Chron and identify rapid Neogene block rotation of a flake within the KOFZ. An inferred maximum slip rate of 0.6 cm/year on this fault zone is comparable with lower estimates of slip on the EAFZ and suggests that most strike slip on the DSFZ is now being partitioned to the west of the Gulf of Iskenderun on a developing strike slip zone linking with the Cyprus Arc.