Evidence of oceanic plate delamination in the Northern Atlantic

Earth is a dynamic planet with its surface constantly recycled by plate tectonics and surface processes. Subduction of oceanic lithosphere and delamination of continental lithosphere are two of the main mechanisms by which the Earth’s lithosphere is recycled back into the mantle. Delamination in continental regions typically occurs below collisional belts due to the separation of the lithospheric mantle from the overlying lighter crust, aided by the existence of weak layers within the continental lithosphere. The oceanic lithosphere is classically pictured as a rigid plate with a strong core that should not allow for delamination to occur at pristine segments of oceanic plates. We will present what may be the first case of oceanic delamination offshore Southwest Iberia. The process seems to be triggered by plate convergence and assisted by a thick serpentinized layer that allows the lower part of the lithosphere to decouple from the overlying crust. Tomography images of a high-velocity anomaly support the hypothesis of ongoing oceanic delamination. We also present a set of numerical models that reproduce the process and suggest that it may facilitate subduction initiation. We further propose that such oceanic delamination is responsible for some of the highest-magnitude earthquakes in Europe, including the M8.5-8.7 Great Lisbon Earthquake of 1755 and the M7.9 San Vincente earthquake of 1969. 

 

This work is supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025 and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). JCD is supported by an FCT contract CEEC Inst. 2018, CEECINST/00032/2018/CP1523/CT0002 (https://doi.org/10.54499/CEECINST/00032/2018/CP1523/CT0002).