Burial and exhumation history of the Daday Unit (Central Pontides, Turkey): implications for the closure of the Intra-Pontide oceanic basin

In northern Turkey, the Intra-Pontide suture zone represents one of the first-order tectonic structures located between the Istanbul-Zonguldak and the Sakarya continental terranes. It consists of an E-W-trending assemblage of deformed and variably metamorphosed tectonic units, including sedimentary rocks and ophiolites derived from a Neo-Tethyan oceanic basin, known as the Intra-Pontide oceanic basin. One of these units is represented by the Daday Unit that consists of a block-in-matrix assemblage derived from supra-subduction oceanic crust and related deep-sea sedimentary cover of Middle Jurassic age. This setting was acquired during Late Jurassic time by tectonic underplating at a depth of 35-42 km associated with blueschist-facies metamorphism (D1 phase). The following D2, D3 and D4 phases produced the exhumation of the Daday Unit up to shallower structural levels in a time span running from the Albian to late Paleocene. The high geothermal gradient detected during the D2 phase indicates that the Daday Unit was exhumed during a continent-arc collisional setting. The tectonic structures of the Intra-Pontide suture zone, resulting from the previously described tectonic history, are unconformably sealed by the upper Paleocene - Eocene deposits. This tectonic setting was intensely reworked by the activity of the North Anatolian Fault Zone, producing the present-day geometrical relationships of the Intra-Pontide suture zone of the Central Pontides.