Constraining ascent rates of diamond-bearing kimberlite magmas using diffusion chronometry

Kimberlite volcanism involves the rapid ascent of mantle-derived magmas that occasionally contain diamonds. Despite their economic importance and relevance to understanding the compositional evolution of the Earth's upper mantle through geologic time, there are many aspects of kimberlite ascent and eruption that remain poorly constrained. Arguably the most important of these is the volatile-driven (i.e., CO2, H2O) ascent velocities of primary kimberlite melts, which are difficult to study due to the intense alteration in most ancient kimberlitic rocks. This project will investigate the geology of two contrasting, but relatively young and well-preserved diamond-bearing kimberlite deposits, in the USA (the Eocene Montana kimberlites) and in Tanzania (the Holocene Igwisi Hills; Brown et al., 2012). The latter is the youngest known kimberlite on Earth and remarkably fresh, containing primary (i.e. magmatic) olivine, calcite, perovskite and apatite. The aim of the project is to determine kimberlite magma ascent velocities, capitalizing on recent advances in diffusion chronometry (Mutch et al., 2019; Costa et al., 2020) as applied to both zoned olivine and apatite phenocrysts, developed for other, more common magma types. The study will provide a novel, quantitative understanding of kimberlite volcanism, and has potential to dramatically improve our understanding of kimberlite ascent and eruption rates.