Slab metamorphism and interface earthquakes in Peru: implications for along-strike fluid content and seismotectonic variation

Evidenced by a typically shallow subducted thick mid-ocean ridge basalt (MORB) layer that dominates the subducting Nazca plate and a significant lack of arc magmatism, the Peruvian megathrust remain enigmatic in thermal regime and petrological metamorphism. Thermally controlled slab dehydration in the incoming plate may facilitate fluids release and migration which possibly causes fault instability and seismic and aseismic slips. We find that (1) the eclogitization of the MORB layer and the harzburgitization of the ultramafic layer, and the subsequent dehydration embrittlement probably affect interface seismicity in Peru; (2) the subduction of the Nazca Ridge separates southern Peru from north-central Peru, leading to a MORB-dominant oceanic lithosphere beneath Peru associated with an aseismic interface at depth and a lack of arc magmatism; (3) slab dehydration of >0.01 wt%/km accompanied by temperatures of 300-600°C possibly affect the occurrence of earthquakes and slips distributed on the hydrated interface. The along-strike fluid content variation possibly interprets the forearc seismotectonic segmentation associated with pore fluid pressure variation on megathrusts.