Exploring southern African Plateau uplift with landscape evolution model inversion and erosion history data
Résumé
The southern African plateau is a dominant feature of African topography but there is considerable debate about
when and how it formed. Cretaceous kimberlite activity and the presence of a large low shear seismic velocity
province (LLSVP) in the deep mantle below southern Africa have lead many to propose uplift related to mantle
processes. Better constraints on the timing of uplift have the potential to constrain the nature of the LLSVP and
the source of support for southern Africa’s anomalous elevations. However, surface uplift is difficult to detect
directly in the geologic record and the relationships between mantle-sourced uplift and erosion are not necessarily
direct. Here, we use a landscape evolution model combined with data constraining the spatiotemporal erosion
patterns across southern Africa to explore how topographic development and erosion are related. This is an ideal
location to utilize this approach because several recent studies have helped to constrain the erosion history of
this region over different spatial and temporal scales but the uplift history is still widely debated. We integrate a
highly efficient landscape evolution model (FastScape, Braun and Willett, 2013) and a thermal module with a large
low temperature thermochronology dataset, sedimentary flux volumes for the major offshore basins, and geologic
observations to address these questions. We used inversion methods based on the Neighborhood Algorithm to
investigate how data is best simulated by the model while varying model parameters related to plateau uplift and
the physical characteristics of the eroding material. This is a powerful approach because we are able to compare
model outputs to many aspects of topographic shape and constraints on the erosion history simultaneously. Results
from the inversions show that the data are sufficient to constrain many model parameters. Additionally, we show
that the combination of different types of data, and in particular the spatiotemporal erosion information from the
thermochronologic results, is valuable for constraining many of these parameters. We show that the geometry
and physical characteristics of the overlying sedimentary basin, as well as the characteristics of the geodynamic
forcing, have significant control on plateau erosion patterns. It is therefore important to consider both geodynamics
and surface controls on erosion when interpreting erosion patterns. Inversion methods with FastScape can be a
valuable tool for examining the linkages between processes at the surface and at depth.