Metamorphic and Tectonic Evolution of the Hırkadağ Block, Central Anatolian Crystalline Complex

Authors: DONNA L. WHITNEY, YILDIRIM DİLEK

Abstract: The Hırkadağ metamorphic block is a NE-SW-trending horst structure that is part of the Kırşehir Massif in the Central Anatolian Crystalline Complex (CACC). Along its southwestern margin, the block contains upper amphibolite facies metapelitic rocks that record peak metamorphic conditions of 670-710 °C, ~ 7 kbar, as determined by garnet-biotite geothermometry and garnet-sillimanite-plagioclase-quartz, garnet-rutile-sillimanite-ilmenite-quartz, and garnet-rutile-ilmenite-plagioclase-quartz geobarometry. A clockwise pressure-temperature path is inferred from thermobarometric results and analysis of reaction textures among aluminous phases. Following this medium-pressure metamorphism, low-pressure - high-temperature metamorphism resulted in widespread replacement of garnet by cordierite + spinel + sillimanite, partial replacement of spinel by corundum, and partial melting to produce granitic leucosomes. Garnet-cordierite thermobarometry indicates that low-P - high-T metamorphism occurred at 3 kbar, > 650 °C. This event may have occurred owing to isothermal decompression at high temperatures, or may have been related to magmatism, similar to intrusion-related low-P - high-T metamorphism elsewhere in the CACC. High-angle normal faults bounding the southwestern and northeastern margins of the block truncate metamorphic structures and a granitic intrusion. These faults are part of a crustal-scale extension zone that uplifted the southern part of the Kırşehir Massif in the Late Tertiary, following its erosional exhumation in the Late Eocene.

Keywords: Central Anatolian Crystalline Complex, Hırkadağ, Kırşehir Massif, Metamorphism, Thermobarometry

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