Localized Cenozoic erosion on the southern African Plateau: A signal of topographic uplift?

Abstract

Constraints on the erosion history of the southern African Plateau have played a key role in the debate over the plateau's age and origins. Previous low-temperature thermochronology from the region has illuminated the Cretaceous erosion history but yielded little insight into Cenozoic erosion patterns. We capitalize on the low-temperature sensitivity of apatites with low effective uranium concentration (eU) from kimberlites and examine a compilation of kimberlite apatite (U-Th)/He dates from across the plateau to investigate Cenozoic cooling. Dates from low-eU (<25 ppm) apatites show a range of Miocene to Cretaceous dates while higher-eU dates are dominantly Cretaceous. Thermal history modeling shows that these data patterns are well replicated by a phase of spatially variable cooling in the Cenozoic that ranges from minimal to 25 °C, equating to as much as ~1250 m of erosion. Not all kimberlites record this cooling phase, but those that do are concentrated near paleo- and modern river valleys. These patterns appear best explained by Cenozoic river incision driven by increased rock uplift that caused associated topographic development. Although more data and different tools are needed to resolve temporal and spatial details, this compilation provides the first glimpse of Cenozoic erosion patterns across the plateau surface from thermochronology.