Towards subduction inception along the inverted North African margin of Algeria? Insights from thermo-mechanical models

Abstract

While ocean subduction at continental margins is a prominent process of plate tectonics, understanding how and where it begins is still being debated, especially because examples of emerging ocean–continent subduction in the world are rare. Northern Algeria is currently undergoing a slow compression deformation due to the ongoing African–Eurasian convergence. Active compressional seismic activity recorded both on land and at sea indicates that the margin might be transitioning from a passive stage to an active one.In order to test this hypothesis, we perform thermo-mechanical models of margin inversion. Varying thermal and rheological parameters as well as the geometry of the margin boundary, we find that tectonic inversion of a young passive margin localizes at the margin toe only if the latter is strongly heated (i.e., with an abrupt thermal gradient between oceanic and continental lithospheres); otherwise, deformation propagates into the weak, hot oceanic lithosphere. The presence of a thinned continental crust at the ocean–continent transition favors either subduction of the oceanic lithosphere when the transition zone plunges towards the continent, or an indentation of the lower continental crust by the oceanic lithosphere when the transition zone is vertical. If the oceanic lithosphere is directly in contact with the continental margin, subduction-like deformation occurs during the early stages of the model but rapidly gives place to intra-oceanic buckling and faulting.Comparing the results of the simulation to the active tectonic structures of the Algerian margin, we conclude that both processes (emerging subduction or indentation) are possible and that the presence of a thermal anomaly beneath the thinned continental margin is probable, in relation with slab rupture at depth or with other thermal weakening processes.