Palaeomagnetic investigation of Cenozoic volcanic rocks bordering the North Anatolian Fault Zone, Reşadiye and Koyulhisar Districts, central-east Anatolia, Turkey

Abstract

A palaeomagnetic study is reported from the lavas of Eocene, Miocene and Pliocene age cropping out immediately to the north of the North Anatolian Fault Zone (NAFZ) in the Reşadiye–Mesudiye region of central-eastern Anatolia. Rock magnetic investigations identify a high percentage of multi-domained magnetite as the dominant ferromagnet in these rocks and this probably accounts for a relatively poor response to alternating field and thermal demagnetisation. Thirty of 37 units yielded acceptable groupings of characteristic magnetisation directions. An earlier study indicated small anticlockwise crustal block rotation in this region since Upper Cretaceous times (D/I = 347/50°), and our study indicates that this was overtaken by clockwise rotation in Eocene times (D/I = 40/47°), although sample size control from the Palaeogene is poor. Results from later Miocene (D/I = 2/62°) and Pliocene (D/I = 0/53°) volcanic rocks indicate that no significant tectonic rotation has occurred in the north of the NAFZ in Neogene times. This contrasts with rotations in the weaker crust comprising the Anatolian collage south of the NAFZ, where differential and sometimes large anticlockwise rotations occurred during the latter part of the Neogene.