Late Cretaceous – Paleogene tectonothermal evolution of the Akdağ Massif in the central anatolian crystalline complex (northern Kayseri, central Turkey)

Abstract

The Central Anatolian Crystalline Complex (CACC) is a Late Cretaceous continental crystalline basement exposed in central Turkey. Here, we report the metamorphic conditions and cooling history of the southern Akdağ Massif, which is the northeastern margin of the CACC. Thermobarometry performed on the garnet-sillimanite-bearing metapelitic rocks indicate ∼5-6 kbar/650-700 °C metamorphic conditions. Following HT-MP metamorphism, conditions of ∼3-4 kbar and ∼720 °C were also recorded by the metapelitic rocks. The replacement of sillimanite, cordierite, and biotite on the rims of garnet indicates LP-HT metamorphism. The HT decompression path described in this study is similar to conditions that have been previously proposed for the CACC. The LP-HT metamorphism resulted from the increased geothermal gradian arising from local granitoid intrusions, which are most likely related to Late Cretaceous subduction below the CACC, at ∼82-72 Ma. The Ar/Ar geochronology indicates that cooling of the high-grade rocks occurred at 75±0.8 Ma and the relatively younger Ar/Ar cooling ages of 61±0.5 Ma (amphibole) and 55.0±0.3 Ma (muscovite) were obtained from the medium/low grade metamorphic rocks of the Akdağ Massif. These cooling ages and stratigraphic evidence from the middle Eocene sedimentary cover, suggests a rapid exhumation and cooling rate of the Akdağ Massif is about ∼40 °C/Ma. We suggest therefore, that the exhumation of the Akdağ Massif was finalized by the Late Paleocene – Early Eocene and we suggest that this rapid exhumation can be explained by tectonic effects rather than by erosional alone.