Numerical modelling of lithosphere-asthenosphere interaction and intraplate deformation in the Gulf of Guinea

To present day, the phenomenon of intraplate deformation and its associated earthquakes remain elusive. In this work, we argue that intraplate deformation may result from the interaction between lithospheric and upper mantle dynamic processes. To this extent, we targeted the Gulf of Guinea and adjacent Western Africa, a region with both low plate velocities and clear asthenosphere dynamics, allowing us to isolate the individual underlying dynamic constraints which govern intraplate deformation. Thus, here we present 3D numerical geodynamic models of the asthenosphere-lithosphere interaction in the Gulf of Guinea, ran with the state-of-the-art modelling code LaMEM. We employ different initial/boundary conditions such as: (a) identical vs different spreading rates for the varying segments of the Atlantic mid-ocean ridge, (b) the presence/absence of weak zones (e.g., the Romanche/Central-African shear zones), and (c) the effect exerted by an active mantle plume, with a varying ascension velocity. Seismicity patterns was used to evaluate the models and their validity. Our results suggest that intraplate deformation within the Gulf of Guinea is influenced by the spreading rate of the mid-ocean ridge, with stress being localized around the ocean-continent transition and existing shear zones. They also suggest that the existence of an underlying stress source (e.g., a mantle plume) beneath the Cameroon region is crucial to explain the epicenter distribution/deformation in the region. • The seismic event distribution in the Gulf of Guinea can be explained by the interaction between two separate stress sources. • The presence of lithospheric weak zones allows the stress from the mid-ocean ridge to be transferred inland, with the seismicity in the Southern part of Ghana partly reflecting this process. • A mantle plume underneath the Cameroon Volcanic Line can explain the seismic events in the region.