Late Cretaceous extensional denudation along a marble detachment fault zone in the Kırşehir massif near Kaman, central Turkey

In the Central Anatolian Crystalline Complex (CACC), 100 km scale metamorphic domains were exhumed in a context of north-south plate convergence during late Cretaceous to Cenozoic times. The timing, kinematics and mechanisms of exhumation have been the focus of previous studies in the southern Niğde Massif. In this study, we investigate the unexplored northern area regarding the tectonic features preserved on the edges of the Kırşehir Massif, based on detailed field-mapping in the Kaman area where high-grade metasediments, non-metamorphic ophiolites and monzonitic plutons are locally exposed together. Close to the contact with the ophiolites, west-dipping foliated marble-rich rocks display mylonites and discrete protomylonites with normal shear senses indicating a general top-to-the W–NW direction. Both of these structures have been brittlely overprinted into cataclastic corridors parallel to the main foliation. The mylonite series and superimposed brittle structures together define the Kaman fault zone. The study of the evolution of calcite deformation fabrics along an EW section supported by Electron Back Scattered Diffraction measurements (EBSD) on representative fabrics indicates that the Kaman fault zone represents an extensional detachment.In Ömerhacılı, in the vicinity of the Baranadağ quartz-monzonite, the metamorphic sequence shows static annealing of the calcite mylonitic fabrics. This evidence suggests that intrusion took place at shallow depth (∼10 km) into an already exhuming metamorphic sequence. As a consequence for the Kaman area, buried metasediments have been rapidly exhumed between 84 and 74 Ma (∼1 km/Ma) where exhumation along a detachment zone, displaying a top-to-the W–NW shear motion, took place in the mid to upper crust prior to magmatic intrusion in the late Campanian. As the intrusion cut through the detachment fault, the main shearing deformation ceased. Brittle tectonics coupled with erosion likely took over during the final unroofing stages at a slower rate (<0.2 km/Ma), until the pertinent rocks reached the Earth’s surface in the late Paleocene.

► An extensional detachment has been discovered in Kırşehir Massif, Central Anatolia.
► Kinematic from calcite mylonitic shear bands points to a top-to-the W–NW motion.
► The exhumation rate was fast prior to monzonitic intrusion at shallow depth.
► Final unroofing stage was accommodated by brittle tectonics coupled with erosion.