Blueschist-facies paleo-earthquakes in a serpentinite channel (Zagros suture, Iran) enlighten seismogenesis in Mariana-type subduction margins

The architecture and pressure-temperature conditions reached by a Cretaceous block-in-matrix serpentinite mélange exposed in the Zagros suture resemble those imaged active Mariana subduction zone. There, large magnitude-earthquakes (M>w9) have never been recorded but smaller events – of poorly-constrained physical origin range M?w3-6 are widespread. Field petro-structural constraints led to first report blueschist-facies seismic fault-related rocks melange, including breccias, foliated cataclasites ultracataclasites; all observed within mafic metatuffaceous block embedded schists. Fine-scale petrological characterization ultrafine-grained, fluidized cataclastic material reveals presence newly-formed glaucophane, lawsonite, phengite, albite pumpellyite, an assemblage inferred (based on thermodynamic modelling) crystallized lower lawsonite-blueschist facies at ?0.6-1.0 GPa 230-300 °C. Extensional veins containing similar mineral assemblages crosscutting aforementioned also identified as comminuted fragments lithologies. Crosscutting relationships among multiple generations ultracataclasites brecciated blueschists suggest that episodic faulting hydrofracturing were contemporaneous processes ?20-35 km depth, i.e., reported for metabasalts expelled mud volcanoes. Mechanical modelling confirms studied features can only formed under nearly lithostatic pore fluid pressure conditions, maintaining system critically unstable regime promoted recurrent faulting, monitored seismogenic These fluids likely associated with externally deeply-generated pulses may window, imprinting Ta-Th-Nb-HREEs-enriched trace element signature. This new faulted blueschist occurrence highlights nature mechanical operating fluid-saturated fault zones serpentinized channel.