Extreme plastic deformation and subsequent Pb loss in shocked xenotime from the Vredefort Dome, South Africa

A study on the Vredefort Dome, South Africa, reveals that extreme plastic deformation in shocked xenotime does not clearly record impact age resetting but instead facilitates subsequent lead (Pb) loss during a younger alteration event. Researchers analyzed a detrital xenotime grain using orientation mapping and secondary ion mass spectrometry (SIMS), identifying planar deformation bands (PDBs) and deformation twins. The U-Pb data yielded a discordia with an upper-intercept age of 2953 ± 15 Ma, consistent with the Kaapvaal craton bedrock, while the lower intercept age of 1754 ± 150 Ma suggests Pb loss during a ca. 1750 Ma alteration episode affecting the Witwatersrand basin. Numerical modeling confirmed this interpretation, indicating that high dislocation density from deformation features enabled later Pb loss rather than recording impact-related resetting.

Cavosie, A. J., Kirkland, C. L., Reddy, S. M., Timms, N. E., Talavera, C., & Pincus, M. R. (2021). Extreme plastic deformation and subsequent Pb loss in shocked xenotime from the Vredefort Dome, South Africa. Large Meteorite Impacts and Planetary Evolution VI, 465–478. https://doi.org/10.1130/2021.2550(20)