The lithospheric architecture of passive margins is crucial for understanding the tectonic processes that caused the break-up of Gondwana. We highlight the evolution of the South Atlantic passive margins by a simple thermal lithosphere-asthenosphere-boundary (LAB) model based on rifting time, crustal thickness, and stretching factors. We simulate the different rifting stages that caused the opening of the South Atlantic Ocean and pick the LAB as the T=1330 °C isotherm, which is calculated by 1D advection and diffusion. In a synthetic example, we demonstrate that the initial crustal thickness has the largest effect on the thermal LAB. For the South American passive margin, our modeled LAB shows a deep and smooth structure between 110-150 km depth at equatorial latitudes and a more variable LAB between 50-200 km along the southern part. This division reflects different stages of the South Atlantic opening: initial opening of the southern South Atlantic causing substantial lithospheric thinning, followed by rather oblique opening of the equatorial South Atlantic accompanied by severe thinning. The modeled LAB reflects a high variability associated with tectonic features on a small scale. Comparing the LAB of the conjugate South American and African passive margins in a Gondwana framework reveals a variable lithospheric architecture for the southern conjugate margins. Along selected conjugate margin segments stark differences up to 80 km of the LAB depths correlate with strong gradients in margin width. This mutual asymmetry suggests highly asymmetric melting and lithospheric thinning prior to rifting.

Recently, the continually increasing availability of seismic data has allowed high-resolution imaging of lithospheric structure beneath the African cratons. In this study, S-wave seismic tomography are combined with high resolution satellite gravity data in an integrated approach to investigate the structure of the cratonic lithosphere of Africa. A new model for the Moho depth and data on the crustal density structure are employed along with global dynamic models to calculate residual topography and mantle gravity residuals. Corrections for thermal effects of an initially juvenile mantle are estimated based on S-wave tomography and mineral physics. Joint inversion of the residuals yields necessary compositional adjustments that allow to recalculate the thermal effects. After several iterations, we obtain a consistent model of upper mantle temperature, thermal and compositional density variations, and Mg# as a measure of depletion, as well as an improved crustal density model. Our results show that thick and cold depleted lithosphere underlies West African, northern to central eastern Congo, and Zimbabwe Cratons. However, for most of these regions, the areal extent of their depleted lithosphere differs from the respective exposed Archean shields. Meanwhile, the lithosphere of Uganda, Tanzania, most of eastern and southern Congo, and the Kaapvaal Craton is thinner, warmer, and shows little or no depletion. Furthermore, the results allow to infer that the lithosphere of the exposed Archean shields of Congo and West African cratons was depleted before the single blocks were merged into their respective cratons.