EGU21-14546, updated on 04 Mar 2021
https://doi.org/10.5194/egusphere-egu21-14546
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Quantifying the erosion of the world’s largest impact crater using cosmogenic nuclides: the Vredefort Dome, South Africa.

Rivoningo Khosa1,2, Stephen Tooth3, Jan Kramers1, Vela Mbele2, Lee Corbett4, and Paul Bierman4
Rivoningo Khosa et al.
  • 1Department of Geology, University of Johannesburg, Johannesburg, South Africa.
  • 2iThemba Laboratory for Accelerator Based Sciences (LABS), Johannesburg, South Africa.
  • 3Department of Geography and Earth Sciences, Aberystwyth University, Wales, United Kingdom.
  • 4Department of Geology, University of Vermont, Burlington, USA.

The world’s largest meteorite impact crater, the Vredefort Dome, has been the subject of extensive studies relating to its age, geology and geomorphology. However, there are no studies pertaining to the rate at which the rocks in the crater remnant are eroding, which can provide insight into the development of the landform over time. This study used the cosmogenic nuclides 10Be and 26Al, extracted from purified quartz samples, to investigate erosion rates along the Vaal River as it traverses the impact crater. The Vaal River flows in mixed bedrock-alluvial terrain through the dome, crossing two different bedrock lithologies. The river is multi-channelled (anabranching) atop the granitoids exposed in the core of the dome, then downstream flows as a single channel through a narrow canyon cut into the quartzites that form the rim of the dome. We collected 14 samples from the two rock types to assess lithologic controls on erosion rate and determine landscape erosion history. Results from the analysis of both isotopes were in close agreement; here, we report outcrop erosion rates based on the 10Be. The average 10Be-determined erosion rates (± 1 SD) along the active river channel for the quartzite (n = 4) and granitoid (n = 6) regions are 1.90 ± 0.12 and 2.19 ± 0.14 m/Ma respectively.  Additional samples from older, now elevated (>5 m) strath terraces developed atop quartzite (n = 4) indicate slightly lower average apparent erosion rates of 1.65 (± 0.09) m/Ma.  The data demonstrate that the erosion rates along the active river channel are similar between the two lithologies despite differences in rock hardness.  The resistant, slowing eroding quartzites serve as the local base level for the river upstream, promoting the development of anabranching, which disperses bedrock erosion over a wider area of the crater. We infer that both bedrock hardness and channel characteristics are important controls on erosion rates along the river.  Collectively, the dataset further illustrates the low bedrock erosion rates that prevail across large areas of the southern African interior.

How to cite: Khosa, R., Tooth, S., Kramers, J., Mbele, V., Corbett, L., and Bierman, P.: Quantifying the erosion of the world’s largest impact crater using cosmogenic nuclides: the Vredefort Dome, South Africa., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14546, https://doi.org/10.5194/egusphere-egu21-14546, 2021.

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