THERMOCHRONOLOGICAL EVIDENCE OF LATE OLIGOCENE AND MID-MIOCENE ACTIVITY ALONG THE NORTH ANATOLIAN FAULT IN SOUTHWESTERN THRACE (TURKEY)

Propagation of the North Anatolian Fault in the Marmara Sea region is dated at the early Pliocene. However, apatite fission-track analyses and thermal modelling of rock samples of similar age and lithology collected across the trace of the Ganos segment of the North Anatolian Fault (NAF) in southwestern Thrace (Turkey) indicate that a significant structural discontinuity was in existence there at least by the latest Oligocene. Such discontinuity had a complex kinematic history, as exhumation south of it occurred during the latest Oligocene and north of it during the mid-Miocene. Our data imply that early Pliocene westward propagation of the NAF in the Marmara region followed a pre-existing structural discontinuity and has not led to a significant vertical offset.

The proto-NAF documented in this paper can be interpreted as the western branch of the Intra-Pontide suture, a Paleogene collision zone related to the opening of the western Black Sea. According to Görür and Okay (1996), the terminal closure of the Intra-Pontide ocean and the development of the Intra-Pontide suture in the Marmara region occurred during the Oligocene. Our data support this interpretation, pointing to a previously unrecognized episode of rapid exhumation of the frontal part of the Thrace forearc basin during latest Oligocene – early Miocene time.