A paper led by Peter Haas (Christian-Albrechts-Uni Kiel, Germany) on modeling the present-day lithosphere thickness along the conjugate South Atlantic margins is accepted and in press for Tectonics.

Key Points:

• A simple thermal LAB model for the South Atlantic passive margins has been developed
• The LAB model shows distinct variations along the margins that correlate with margin widths
• Conjugate margin pairs reflect an asymmetry in LAB depth patterns that are locally related to post break-up lithospheric thinning

Abstract:

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 onset and cessation of rifting, crustal thickness, and stretching factors. We simulate lithospheric thinning and select the LAB as the T=1330 °C isotherm, which is calculated by 1D advection and diffusion. Stretching factors and margin geometry are adjusted to state-of-the-art data sets, giving a thermal LAB model that is especially designed for the continental margins of the South Atlantic. Our LAB model shows distinct variations along the passive margins that are not imaged by global LAB models, indicating different rifting mechanisms. For example, we model up to 200 km deep lithosphere in the South American Santos Basin and shallow lithosphere less than 60 km in the Namibe Basin offshore Africa. These two conjugate basins reflect a strong asymmetry in LAB depth that resembles variations in margin width. In a Gondwana reconstruction, we discuss these patterns together with seismic velocity perturbations for the Central and Austral Segments of the margins. The shallow lithosphere in the Namibe Basin correlates with signatures of the Angola Dome, attributed to epeirogenic uplift in the Neogene, suggesting an additional component of post-break up lithospheric thinning.