Cooling history of the Chapedony metamorphic core complex, Central Iran: Implications for the Eurasia–Arabia collision

Abstract

New apatite and zircon (U–Th)/He thermochronometry is used to constrain the late-stage cooling history of the Chapedony metamorphic core complex in the Saghand region of Central Iran, providing new constraints on the Cenozoic tectonic evolution of this segment of the Euro–Arabian collision zone. Zircon and apatite He ages from the footwall indicate that it cooled to near-surface temperatures by 30Ma. Combined with previous high temperature thermochronology, the new data require that the Chapedony metamorphic core complex cooled from ~750°C to ~60°C in less than 20million years (at ~80°C/Myr). Cooling of the complex occurred through tectonic exhumation at a rate of 1.2–1.5km/Myr. Exhumation of the core complex occurred during the main phase of subduction of the distal Arabian margin beneath the Central Iranian Plate at 49 to 30Ma. Zircon He ages from the hangingwall units of the complex suggest an earlier pulse of exhumation in Middle–Late Cretaceous. Apatite He ages from the hangingwall (22–30Ma) are significantly younger than the core complex exhumation but is consistent with the regional timing of initial Eurasia–Arabia collision.