Timing of high-grade metamorphism in central Turkey and the assembly of Anatolia

The timing of metamorphism of the crystalline massifs in western and central Turkey (Menderes, Kirşehir, Niǧde, Akdaǧ) is important information for understandilng the assembly of Anatolia and the thermal-tectonic evolution of the Turkish segment of the Alpine-Himalayan belt. The high-grade basement rocks of the massifs are polymetamorphic, and the complexity of interpreting ages obtained from zircon and other minerals has led to a longstanding debate about the significance and regional extent of Neoproterozoic v. younger (Mesozoic, Cenozoic) metamorphism. New U-Pb SHRIMP (sensitive high-resolution ion microprobe) analyses of monazite from a garnet-sillimanite gneiss in the Kirşehir Massif, central Anatolia, document Late Cretaceous (84.1 ± 0.8 Ma) high-temperature metamorphism. This Late Cretaceous age for central Anatolian metamorphism is at least 50 Ma older than Alpine metamorphism in the Menderes Massif in western Turkey. Models that propose a continuous Anatolide-Tauride tectonic zone, with central Anatolia as a promontory, cannot explain such a large time difference within a small region. Unless the Menderes ages have been reset by Aegean thermal-tectonic events, Anatolia probably formed from a collage of continental fragments rather than by simple collision of an irregular Tethyan platform with Eurasia.