Oceanic intraplate faulting as a pathway for deep hydration of the lithosphere: Perspectives from the Caribbean

The recycling of water into the Earth's mantle via hydrated oceanic lithosphere is believed to have an important role in subduction zone seismicity at intermediate depths. Hydration of oceanic lithosphere has been shown to drive double planes of intermediate-depth, Wadati-Benioff zone seismicity at subduction zones. However, observations from trenches show that pervasive normal faulting causes hydration similar to 25 km into the lithosphere and can explain neither locations where separations of 25-40 km between Wadati-Benioff zone planes are observed nor the spatial variability of the lower plane in these locations, which suggests that an additional mechanism of hydration exists. We suggest that intraplate deformation of >50-m.y.-old lithosphere, an uncommon and localized process, drives deeper hydration. To test this, we relocated the 25 November 2018 6.0 M-W Providencia, Colombia, earthquake mainshock and 575 associated fore- and aftershocks within the interior of the Caribbean oceanic plate and compared these with receiver functions (RF) that sampled the fault at its intersection with the Mohorovicic discontinuity. We examined possible effects of velocity model, initial locations of the earthquakes, and seismic-phase arrival uncertainty to identify robust features for comparison with the RF results. We found that the lithosphere ruptured from its surface to a depth of similar to 40 km along a vertical fault and an intersecting, reactivated normal fault. We also found RF evidence for hydration of the mantle affected by this fault. Deeply penetrating deformation of lithosphere like that we observe in the Providencia region provides fluid pathways necessary to hydrate oceanic lithosphere to depths consistent with the lower plane of Wadati-Benioff zones.