Amphibolite facies metamorphism in lower Witwatersrand Supergroup rocks exposed in the Vredefort Dome – a Ventersdorp LIP connection

A new study reveals that amphibolite facies metamorphism in the lower Witwatersrand Supergroup rocks at the Vredefort Dome is linked to the early stages of magmatism associated with the Ventersdorp Large Igneous Province (LIP), rather than the later Bushveld Complex. The research, using microtextural and mineral compositional analysis alongside THERMOCALC calculations, identified two distinct metamorphic events with different pressure-temperature conditions preceding the Dome-forming meteorite impact 2.02 billion years ago. Garnet Sm-Nd chronology dated the first event (M1) to approximately 2.796 billion years, aligning it with the early Ventersdorp LIP activity. While a second event (M2) showed elevated heat flow consistent with Bushveld Complex emplacement, thermal modeling suggested both events were influenced by local perturbations from contemporaneous sill intrusion. This challenges previous assumptions about the timing and causes of metamorphism in this UNESCO World Heritage Site.

Beaton, K. J., Gibson, R. L., Bybee, G. M., Walker, S., Diener, J. F. A., & Baxter, E. F. (2022). Amphibolite facies metamorphism in lower Witwatersrand Supergroup rocks exposed in the Vredefort Dome – a Ventersdorp LIP connection. South African Journal of Geology, 125(2), 191–210. https://doi.org/10.25131/sajg.125.0016