ÇAĞRILI KONUŞMALAR / KEYNOTES Invited Speeches ... - TPJD

Tectono-Sedimentary Evolution of the Upper Cretaceous – Middle Eocene
Central Anatolian Basins, Turkey: Summary and New Tectonic Model
Steven Nairn 1 , Alastair Robertson 2 , Ulvican Ünlügenç 3 , Kemal Taslı 4 , Nurdan İnan 4
1 University of Cambridge, UK
2 University of Edınburgh, School of Geosciences, UK
3 Çukurova University, Department of Geological Engineering, Adana
4 Mersin University, Department of Geological Engineering, Mersin
5 Department Geological Engineering, Mersin University, Mersin, Turkey
In central Turkey, a strand of the former northern Neo-Tethys Ocean (İzmir-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 Niğde-Kırşehir). The resulting
suture zones encompass Upper Cretaceous to Middle Eocene basins including the Kırıkkale,
Haymana, Tuz Gölü and Çankırı basins. The basement comprises the Ankara Mélange, a mainly
Cretaceous accretionary complex together with the western margin of the Niğde-Kırşehir Massif,
an inferred microcontinent. New geochemical data from beneath the Kırıkkale Basin identifies
mid ocean-ridge basalt, here interpreted as Upper Cretaceous Neo-Tethyan oceanic crust.
During the latest Cretaceous, the Kırıkkale and Tuz Gölü basins formed in deep water on MORB
crust, bordered by the Niğde – Kırşehir microcontinent to the east. Further west, the Haymana
Basin is an accretionary forearc basin constructed on the Ankara Mélange. The Çankırı Basin
further north developed on accretionary mélange 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 İzmir-Ankara ocean,
triggering the genesis of supra-subduction zone oceanic lithosphere. The subduction zone then
rolled back southwards until it collided with the Niğde – Kırşehir microcontinent, again emplacing
ophiolites (e.g. Çiçekdağ) during latest Cretaceous time. However, vestiges of Neotethyan
MORB remained to the west of the Niğde – Kırşehir microcontinent, forming the basement of
the Kırıkkale and Tuz Gölü 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.
Keywords : Central Anatolia, sediments, tectonics, models
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