Crustal disequilibrium of the central Pontides (northern Turkey) due to oroclinal bending revealed by gravity modelling

Abstract

The Turkish Pontide orogenic belt belongs to the former Eurasian margin, which is the result of two major successive processes of the closure of the Tethyan oceans: subduction followed by collision. This almost E-W trending large mountain range shows an arc-shaped geometric structure in the northern Turkey. According to previous studies based on geological and paleomagnetic data, oroclinal deformation was proposed as a result of the geodynamic evolution due to the Africa-Eurasia convergence in the region. The aim of study is to determine how this important evolution is expressed in the lithosphere beneath the region by gravity modelling.A Bouguer gravity anomaly map was constructed and from this a gravity model is presented that reveals the general crustal structure underneath the northern Turkey. The results present a significant crustal thickness change that occurs in the N-S and as well as in the E-W directions. From S to N, a significant sharp crustal thickness decrease (~20 km) was found, while from E to W the crustal thickness beneath the Pontides increases by approximately 7 km.While an average thickness of 37 km was calculated in the East, it reached a maximum value of ~44 km in the West. Although the reason for the increase in crustal thickness from north to south is logical in terms of the geodynamic evolution, the increase from east to west is probably caused by the nature of the continental collision. The most plausible explanation is an (oblique) NW indentation of the Kırşehir Block into the Pontides.