Tectono-Sedimentary Evolution of the Upper Cretaceous – Middle Eocene Central Anatolian Basins, Turkey: Summary and New Tectonic Model

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In central Turkey, a strand of the former northern Neo-Tethys Ocean (Izmir-Anzara-Erzincan ocean) subducted northwards under the Pontide active margin during Cretaceous – Early Cenozoic time. Subduction generated accretionary complexes and emplaced ophiolites onto the former passive margins of microcontinents (e.g. Tauride-Anatolide Nigde-Kirsehir). The resulting suture zones encompass Upper Cretaceous to Middle Eocene basins including the Kirikkale, Haymana, Tuz Golu and Cankiri basins. The basement comprises the Ankara Melange, a mainly Cretaceous accretionary complex together with the western margin of the Nigde-Kirsehir Massif, an inferred microcontinent. New geochemical data from beneath the Kirikkale Basin identifies mid ocean-ridge basalt, here interpreted as Upper Cretaceous Neo-Tethyan oceanic crust. During the latest Cretaceous, the Kirikkale and Tuz Golu basins formed in deep water on MORB crust, bordered by the Nigde – Kirsehir microcontinent to the east. Further west, the Haymana Basin is an accretionary forearc basin constructed on the Ankara Melange. The Cankiri Basin further north developed on accretionary melange bounded by the Pontide active margin to the north. Palaeocene sedimentation was dominated by shallow-marine coralgal reef facies. Latest Palaeocene – Middle Eocene facies include shelf-type Nummulitic limestone, locally deposited on unconformity surfaces. In one model, the basins formed on obducted ophiolites following Late Cretaceous closure of a single northern Neo-Tethyan ocean. In an alternative model, the basins evolved in a forearc setting associated with northward subduction until the Middle Eocene. We propose a new model in which two north-dipping subduction zones were active during the late Mesozoic in the northern Neo-Tethyan region (distinct from the S Neotethys). In the south, ophiolites formed above a N-dipping subduction zone consuming oceanic crust adjacent to the Tauride-Anatolide continent (Inner Tauride Ocean) until the southward retreating trench collided with the northern margin of the continent emplacing ophiolites (e.g. Alihoca ophiolite). In the north, subduction initiated outboard of the Eurasian margin within the Izmir-Ankara ocean, triggering the genesis of supra-subduction zone oceanic lithosphere. The subduction zone then rolled back southwards until it collided with the Nigde – Kirsehir microcontinent, again emplacing ophiolites (e.g. Cicekdag) during latest Cretaceous time. However, vestiges of Neotethyan MORB remained to the west of the Nigde – Kirsehir microcontinent, forming the basement of the Kirikkale and Tuz Golu Basins. Continuing latest Palaeocene – Middle Eocene northward subduction culminated in final continental collision and the development of an Anatolia-wide unconformity, although strong uplift was delayed until Plio-Pleistocene.