Gneiss domes, metamorphic core complexes, and wrench zones: Thermal and structural evolution of the Niğde Massif, central Anatolia

Abstract

The Niğde Massif, a migmatite‐cored structural dome in south central Turkey, was metamorphosed, deformed, intruded, and exhumed in an oblique tectonic regime involving a switch from transpression (prograde metamorphism) to transtension (exhumation). An 80 Ma history of transpression and transtension is recorded in metamorphic rocks of the massif, and the last ∼50 Ma are recorded in both basement and overlying basin deposits. Niğde metamorphic rocks record a high‐temperature, top‐to‐north, syntranspression ductile fabric that was overprinted by lower‐grade, top‐to‐south, syntranstension ductile shear zones. The 40Ar/39Ar data for hornblende, muscovite, and biotite document rapid Late Cretaceous cooling, with the oldest Ar hornblende ages (88–79 Ma) overlapping U‐Pb ages in monazite and zircon (92–78 Ma). Muscovite Ar ages are dominantly 81–79 Ma, suggesting a short time between crystallization of high‐temperature metamorphic rocks and their cooling. Biotite Ar ages are 79–74 Ma, with the exception of disturbed samples from the eastern margin of the massif and from Eocene granitic stocks in the dome core. The eastern margin, adjacent to the sinistral Central Anatolian Fault Zone, records another cycle of burial and exhumation that overprinted earlier fabrics and disturbed isotopic systems. These two cycles of burial‐exhumation took place repeatedly along the same zone; this may be characteristic of highly oblique tectonic regimes. In the Niğde Massif, burial and exhumation became more localized and of lower amplitude over time, suggesting stabilization of the crust.