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 Comp lex (CACC), a microcontinent within the Turkish segment of the Alpine-Himal ayan orogen, vary dramatically from north to south. This variation correlat es with differences in the obliquity of convergence of the continental frag ment relative to the Pontide belt (for the northern CACC) and the Tauride b elt (for the southern CACC). The northern CACC was deformed and metamorphos ed during Late Cretaceous orogen-normal collision and was exhumed from the mid-crust to shallow crustal levels (< 2 kin depth) primarily by erosion as evidenced by an extensive unroofing sequence nearby. Apatite FT ages from two massifs (Kirsehir, Akdag) in the northern CACC range from similar to 32 to 47 Ma and these rocks cooled slowly at similar to3 degreesC/m.y. from > 50 Ma to the present. In contrast, the southern CACC (Nigde Massif) was in itially 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 nort hern CACC. Apatite FT ages for the Nigde core complex range from similar to 9 to 12 Ma and exhumation resulted in slow to moderate cooling at rates of 30 degreesC to 8 degrees /m.y. The northern massifs were therefore exhumed to < 2 km depth while the Nigde rocks remained above the apatite FT closure temperature. The Nigde core complex was unroofed primarily by tectonic den udation along low-angle detachment faults because the faults clearly bound the core and there is very little in the way of detritus that records unroo fing. This is different from core complexes described for the Aegean and ot her extensional regimes worldwide because it developed in a highly oblique (wrench) zone. The broad zone of wrenching subsequently evolved into a narr ow brittle fault zone that is intermittently seismically active today. (C) 2001 Elsevier Science BN. All rights reserved.