Evolution of the Gölbaşi basin and its implications for the long-term offset on the East Anatolian Fault Zone, Turkey

The left lateral East Anatolian Fault Zone (EAFZ) is one of the most active major neotectonic structures of the Eastern Mediterranean region. The fault zone runs for a distance of about 550. km between Karliova in northeast and Mediterranean Sea in southwest. Several fault-parallel basins (such as Hazar and Gölbaşi basins) have been forming along the fault zone. The Gölbaşi basin is the largest basin along the EAFZ and it is located near the junction of the çelikhan-Erkenek and Gölbaşi-Türkoĝlu segments of the EAFZ. Different interpretations including pull-apart, fault wedge and fault ramp basin were made about the evolution of the basin in previous studies. Detailed mapping shows that the çelikhan-Erkenek and Gölbaşi-Türkoĝlu segments are connected by a releasing bend around Gölbaşi Lake. Our study also suggests that Gölbaşi basin was a wide river valley in which the Aksu River flowed and occupied by a large lake. The valley was blocked by a large landslide at least 31,600 ± 500 years ago in the northeastern corner of the basin and as a result, the Aksu River was captured to the SW corner of the basin. Our scenario implies that the Aksu River valley is left laterally offset by the EAFZ about 16.5 ± 0.5. km, which is the largest documented morphological offset on the EAFZ.