From rifting to oceanization in the Gulf of Aden: Insights from 2D numerical models

We investigate the evolution of the Gulf of Aden from rift initiation to the development of active oceanic spreading center by means of 2D thermo-mechanical numerical models, in which the formation of oceanic crust and serpentinite due to the hydration of the uprising mantle peridotite has been implemented. Our analysis highlights that evolution of the models is characterized by four main tectonic phases: a) a first phase (phase I) characterized by low deformation rates throughout the divergent crustal blocks, except near the future ridge where a high crustal velocity gradient generates an intense strain rates; b) a second phase (phase II) during which the crust undergoes an intense, stable and widespread strain, with the localization of the thinning near the future ridge that ends into crustal breakup c) a third phase (phase III) that characterizes the post- crustal breakup evolution of the models during which a mechanical relaxation of the system and a continuum decreasing of the strain rate can be observed, until the occurrence of lithospheric breakup, and d) fourth phase (phase IV) that lasts up to the end of the evolution and during which the two continental blocks move rigidly. We also find that the timing of mantle serpentinization is not affected by the initial thermal configuration of the lithosphere, but a relationship with the crustal thickness can be observed. Rather, the timing of mantle partial melting strongly depends on the initial thermal conditions of both the lithosphere and the crust. We constrain the crustal and lithospheric thickness at 40 and 150 km, respectively, considering the timing of breakup that occurs 20 Myr after the onset of the extension for 0.05% percentage of mantle hydration (in agreement with magma-poor rift margins). Finally, model prediction supports the hypothesis that the Gulf of Aden developed as a slow passive rift of a thin lithosphere with a thick crust and the variation of the features along the passive margins could be related to a lateral variation in the amount of H2O in the mantle, which determines different timing in the mantle melting.