Speaker: Dr. Jean Braun (University of Joseph Fourier--Grenoble)

Abstract:

Dynamic topography is generated by the viscous stress exerted at the base of the lithosphere by the convecting mantle. Constraining the potential contribution of past and present dynamic topography to vertical surface uplift has become essential to comprehend parts of the geological record, but also to validate mantle flow models. For example, episodes of rapid, yet extensive erosion of continental interiors, such as the Late Cretaceous erosional event that affected the southern African craton, can only be explained by large-scale vertical uplift/subsidence generated in the mantle. But how can low amplitude, long wavelength dynamic topography be rapidly eroded is poorly understood. Using novel numerical methods to solve the basic laws governing the evolution of landforms on geological time scales, I will provide a simple explanation for this paradox and apply it to understand the large erosional events that accompanied uplift of the Colorado Plateau and the South African Plateau, respectively. In the second part of my presentation, I will also discuss how lateral variations in surface rock density can strongly affect the response of the crust/lithosphere system to surface erosion and propose how it can explain why, despite its relatively high density, the metamorphic core of many orogenic belts, such as the Tauern Window in the Eastern Alps, is found at the highest topographic levels.