Lu-Hf dating of Jurassic eclogites of the Zagros hinterland, Iran: Implications for the timing of Neotethyan subduction initiation

The Sanandaj-Sirjan zone (SaSZ) on the northern edge of the Arabia-Eurasia suture in Iran includes a significant high-pressure (HP) metamorphic suite exposed along the upper Zayanderud River north of Shahrekord. Phengitic micas from eclogite in the Zayanderud metamorphic complex (ZMC) yielded ⁴⁰Ar/³⁹Ar dates ranging from 184 to 173 Ma ^[1], whereas zircon from an associated anatectic pegmatite gave an average U-Pb age of 176 ± 3 Ma ^[2]. These data are consistent with a subduction channel metamorphism and rapid exhumation during the Early to Middle Jurassic. To constrain the timing of high-pressure conditions, we have conducted Lu-Hf mineral-whole rock dating on two eclogite samples. The resulting garnet-controlled isochron dates of 171.4 ± 0.4 (MSWD = 1.2) and 175 ± 1 (MSWD = 0.43) Ma have important geodynamic implications as the Jurassic initiation of the Neotethyan subduction in Iran has recently been disputed ^[3][4]. The metamorphic ages of the ZMC eclogite now leave no doubt that subduction was ongoing along the SaSZ peri-Tethyan margin during the Middle Jurassic.

[1] Davoudian et al., 2016 Gondwana Research 37: 216-240; [2] Jamali Ashtiani et al., 2020 Gondwana Research 82: 354-366; [3] Azizi & Stern, 2019 Terra Nova 31: 415-423; [4] Lechmann et al., 2018 Contrib. Mineral. Petrol. 173 (12): 102