Thomas Theunissen

Long-term coupling and feedbacks between surface processes and tectonics during rifting: from proximal to distal domains

Thomas Theunissen, Ritske S. Huismans

Whereas significant efforts have been made to understand the relationship between mountain building and surface processes, limited research has been done on the relationship between surface processes and extensional tectonics. Here we present high-resolution 2-D coupled tectonic-surface processes modeling of extensional basin formation. The main aim is to find out how erosion and deposition affect the deformation in extensional systems. We test the combined effects of crustal rheology and varying surface process efficiency (erodibility, sea level) on structural style of rift and passive margin formation. The results show that both erosion of rift flank areas and basin deposition enhance localization of crustal deformation. Frictional-plastic extensional shear zones accumulate more deformation during a longer period of time, and loading of offshore basins can generate crustal ductile flow. Synthetic normal faults system in the proximal domain are enhanced by both erosion of footwall and deposition on the hangingwall. Feedbacks with distal margin formation are more contrasted. In case of wide margin, sediment export is limited as a results of absent rift flank topography. Sediment export to the distal margin is enhanced by a low sea level. In extreme cases sediment deposition delays lithospheric rupture. In case of narrow margin, sedimentation on distal margin can enhance extreme thinning. These mechanisms are enhanced when fluvial erosion, transport and deposition are efficient. We show that removal of mass from rift flanks and sedimentary loading in the basin area provide a first order feedback with tectonic deformation and control on rifted margin tectonic-morphology. However, surface processes do not change the first order structural style of rifting, which is largely controlled by crustal rheology. Rift escarpment morphology is function of paleo-topography and sea level. Variation of strain localization in natural rift systems correlates with the observed behavior and suggests similar feedbacks as demonstrated by the forward numerical models.