Lorenz Michel

Evolution of rift structures, topography and the sediment supply – A perspective from numerical modelling on the respective importance of tectonic and earth surface processes during continental rifting

Lorenz Michel

Continental rifting is the response of the continental lithosphere to extension, and the subsequent evolution of the elevated rift shoulders and subsided basins is complex, depending on the respective contributions from tectonic and earth surface processes. Here, we use a coupled, numerical model in order to see how tectonic and earth surface processes impact the evolution of rifts. We test the sensitivity of the models to different combinations of rheology, extension rate and erosional efficiencies, and investigate the structural and topographic evolution of the rifts, and the associated sediment flux and sediment volumes.

We observe, that the amount of strain localization is critical in driving the structural evolution of the modelled rifts: Systems with slow extension, a high crustal strength and efficient surface processes show a high degree of strain localization, resulting in less faults being active, and more offset on them. The amount of fault offset is also highly sensitive to the erosional efficiency, and more efficient erosion leads to more fault offset, suggesting a strong feedback effect between tectonic and earth surface processes. In terms of the temporal evolution, there is a characteristic sequence for the peaks in (1) uplift, (2) topography and (3) sediment flux, with lag times between the single peaks depending on the extension rate (being between 2 – 5 Myr). We also identify a characteristic pattern for the temporal evolution of the sediment flux with six phases, which are related to the geomorpho-tectonic evolution of the rift. The magnitude of the total sediment volume produced during rifting depends on the degree of strain localization, such that systems with strong crust, slow extension and efficient surface processes produce most sediment. Importantly, we observe that for slower extension more sediment is produced (despite the lower uplift rate), which is related to the stronger feedback effect. As a summary, our models point towards a complex interaction between tectonic and earth surface processes, which has a strong impact on the evolution of structures, topography and the sediment flux during rifting.