Cooling and deformation history of the Çataldağ Metamorphic Core Complex (NW Turkey)

Abstract

Abstract The Cataldag Metamorphic Core Complex (CMCC) consists of the Latest Eocene-Early Oligocene (34–32 Ma) Turfaldag gneiss-migmatite complex (TGMC) and an Early Miocene (21 Ma) Cataldag synkinematic pluton (CSP) which were exhumed as a dome-shaped core complex in the footwall of the Cataldag Detachment Fault Zone (CDFZ) in the Early Miocene. Microstructural features of the Cataldag Metamorphic Core Complex (CMCC) and a two-feldspar geothermometry were studied to understand the cooling and deformation mechanisms. Microtectonic analyses of the TGMC and CSP show that the quartz, feldspar, and mica minerals underwent continuous deformation from ductile to brittle conditions during cooling of the CMCC. Two main deformation zones were determined according to temperature and strain intensity: a ductile deformation zone (DZ) within the central zones of the TGMC and CSP, and a mylonitic zone (MZ) within the peripheral zones of the TGMC and CSP (close to the CDFZ). Within the ductile zone, K-feldspar displays microcline twinning, myrmekite along the K-feldspar megacryst and flame-shaped perthite, and quartz displays chessboard extinction, grain boundary migration, and sub-grain rotation recrystallisation. These microstructures indicate that deformation temperature reached about 600 °C. Under high strain intensity along the CDFZ, the DZ microstructures turn to MZ microstructures. In the MZ, protomylonitic gneiss and mylonitic schists show distinct foliation and their K-feldspar and micas display C-S structures. The feldspars show bulging recrystallisation, a feldspar-fish structure, and domino-type microfractures, while the quartz displays ribbon structures, indicating ductile-to-brittle deformation with temperatures ranging from 500 °C to 500 °C/my) along the CDFZ in the Early Miocene (21 Ma). The shear zone-controlled CSP was emplaced into shallow levels of the Anatolian extending crust, deformed progressively (ductile-to-brittle) along the CDFZ, and cooled rapidly (>500 °C/my) in the Early Miocene (21 Ma). Together, the microstructure, two-feldspar geothermometry and thermochronology data indicate that the TGMC and CSP, which were emplaced into different crustal levels and in different periods, suffered continuous ductile-to-brittle deformation and were exhumed together along the CDFZ during the Early Miocene under the N-S extensional regime in western Anatolia.