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 east-west trending assemblage of deformed and variably metamorphosed tectonic units, including sedimentary rocks and ophiolites derived from a NeoTethyan oceanic basin, known as Intra-Pontide oceanic basin. One of these units is represented by the Daday Unit that consists of an assemblage of block-in-matrix derived from a supra-subduction oceanic crust and related deep-sea sedimentary cover of Middle Jurassic age. This setting has been acquired during the Late Jurassic by underplating at 26-38 km of depth associated with blueschist facies metamorphism (D1 phase). The following D2, D3 and D4 phases developed in a time span running from Albian to late Paleocene during the exhumation of the Daday Unit from 26-38 km to uppermost structural levels. The high geothermal gradient detected during the development of the D2 phase seems to be consistent with the exhumation of the Daday Units 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 late 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 central Pontides.