Retracing the path of kimberlite melt composition

Kimberlites are complex volcanic eruptions that have ferociously traversed more than a hundred kilometers of rock from source to surface.

One of the biggest challenges lies in trying to determine the nature of primary kimberlite melt at depth, prior to its eruption through the continental lithosphere.

A recent study by Andrea Giuliani and colleagues demonstrates that much of the major element compositional variability of kimberlites is controlled by the entrainment of lithospheric mantle material.

Two linear correlations are established upon comparing kimberlites worldwide:

1) a positive correlation between the Mg/Si ratio of the bulk kimberlite and its peridotitic xenoliths, and

2) a positive correlation between the Mg# of mantle-derived olivine cores (xenocrystic) and their rims (magmatic).

These simple, but robust, relationships greatly improve our ability to take the kimberlites we see at surface and retrace their compositional evolution back down into the mantle. The results support the view that kimberlites start as low-degree carbonate-rich melts that are broadly similar from locality to locality.

Read more here

Polished drill core sample of kimberlite from the Jwaneng mine in Botswana. Kimberlite is a mixture of coarse- and fine-grained minerals from the kimberlite magma, and also minerals incorporated from the lithospheric mantle during ascent. Photo by Karen Smit.