Transient, synobduction exhumation of Zagros blueschists inferred from P-T, deformation, time, and kinematic constraints: Implications for Neotethyan wedge dynamics

摘要

We present the first P-T, deformation time, and kinematic constraints on the only known blueschist facies rocks (BS) present in the Zagros (Hajiabad area). The BS were underplated below the Sanandaj-Sirjan zone and crop out as kilometer-scale bodies within extensive colored melange units marking discontinuously the Neotethyan suture zone. P-T estimates point to high-pressure/low-temperature (HP-LT) conditions around 11 kbar and 520–530°C for the majority of BS, along a ～15°C km?1 gradient. Some exotic blocks in matrix serpentinite reached 17–18 kbar at ～500°C. In situ laser probe 40Ar-39Ar radiometric age constraints on phengite cluster between 85 and 95 Ma and suggest that (1) synconvergence exhumation of Zagros BS from 35–50 km to depths <15–20 km was accomplished before 80 Ma, (2) BS exhumation corresponded to a transient process with respect to the long-lived subduction beneath Iran (～150–35 Ma), and (3) age constraints for Zagros BS are 5–10 Myr older than for the nearby Oman HP-LT rocks and broadly coincide with obduction processes in the region (circa 95–70 Ma).