Effects of plate convergence obliquity on timing and mechanisms of exhumation of a mid-crustal terrain, the Central Anatolian Crystalline Complex

Apatite fission-track (FT) ages from the Central Anatolian Crystalline Complex (CACC), a microcontinent within the Turkish segment of the Alpine-Himalayan orogen, vary dramatically from north to south. This variation correlates with differences in the obliquity of convergence of the continental fragment relative to the Pontide belt (for the northern CACC) and the Tauride belt (for the southern CACC). The northern CACC was deformed and metamorphosed during Late Cretaceous orogen-normal collision and was exhumed from the mid-crust to shallow crustal levels ( < 2 km depth) primarily by erosion as evidenced by an extensive unroofing sequence nearby. Apatite FT ages from two massifs (Kirşehir, Akdaǧ) in the northern CACC range from ~ 32 to 47 Ma and these rocks cooled slowly at ~ 3°C/m.y. from > 50 Ma to the present. In contrast, the southern CACC (Niǧde Massif) was initially deformed and metamorphosed during Late Cretaceous contraction, but subsequently developed as a metamorphic core complex in a wrench-dominated regime and was exhumed to < 2 km depth at least 20 m.y. later than the northern CACC. Apatite FT ages for the Niǧde core complex range from ~ 9 to 12 Ma and exhumation resulted in slow to moderate cooling at rates of 30°C to 8°C/m.y. The northern massifs were therefore exhumed to < 2 km depth while the Niǧde rocks remained above the apatite FT closure temperature. The Niǧde core complex was unroofed primarily by tectonic denudation along low-angle detachment faults because the faults clearly bound the core and there is very little in the way of detritus that records unroofing. This is different from core complexes described for the Aegean and other extensional regimes worldwide because it developed in a highly oblique (wrench) zone. The broad zone of wrenching subsequently evolved into a narrow brittle fault zone that is intermittently seismically active today.