Nature: Scientific Reports: A 5‑km‑thick reservoir with > 380,000 km3 of magma within the ancient Earth’s crust

Rais Latypov, Sofya Chistyakova, Richard A. Hornsey, Gelu Costin & Mauritz van der Merwe



Several recent studies have argued that large, long-lived and molten magma chambers may not occur in the shallow Earth’s crust. Here we present, however, field-based observations from the Bushveld Complex that provide evidence to the contrary. In the eastern part of the complex, the magmatic layering continuously drapes across a ~ 4-km-high sloping step in the chamber floor. Such deposition of magmatic layering implies that the resident melt column was thicker than the stepped relief of the chamber floor. Prolonged internal differentiation within this thick magma column is further supported by evolutionary trends in crystallization sequence and mineral compositions through the sequence. The resident melt column in the Bushveld chamber during this period is estimated at > 5-km in thickness and > 380,000 km3 in volume. This volume of magma is three orders of magnitude larger than any known super-eruption in the Earth’s history and is only comparable to the extrusive volumes of some of Earth’s large igneous provinces. This suggests that super-large, entirely molten, and long-lived magma chambers occur, at least occasionally, in the geological history of our planet. Therefore, the classical view of magma chambers as ‘big magma tanks’ remains a viable research concept for some of Earth’s magmatic provinces.

Latypov, R., Chistyakova, S., Hornsey, R. A. & Costin, G. (2022). A 5 ‑ km ‑ thick reservoir km 3 of magma within the ancient Earth ’ s crust. Scientific Reports. Nature Publishing Group UK 1–12.

Lithos: Correlations between olivine composition and groundmass mineralogy in Sierra Leone kimberlites provide constraints on craton-specific melt-lithosphere interactions

Anton Viljoen, Geoffrey H. Howarth, Andrea Giuliani, Angus Fitzpayne, Gelu Costin



Sierra Leone contains two Jurassic-aged diamondiferous kimberlite clusters, namely Koidu and Tongo-Tonguma (hereafter referred to as Tongo), consisting of eruptive pipes and NE-SW trending dikes. In this study, a combination of detailed petrography, and phlogopite, spinel, and olivine compositions in hypabyssal samples is presented to classify and constrain the petrogenesis of these kimberlites. Both the Koidu and Tongo rocks are predominantly macrocrystic and highly micaceous with phlogopite abundances, normalised to olivine-free, of 36–65 vol% in the groundmass. These phlogopite contents are comparable to those of some cratonic lamproites and significantly higher than any other kimberlites. Other groundmass minerals include spinel, perovskite, and apatite set in a base of carbonate and serpentine. Phlogopite and spinel have similar compositions in the Koidu and Tongo samples, displaying evolutionary trends consistent with those observed in worldwide kimberlites. Olivine macrocrysts and microcrysts display complex zoning with distinct cores, internal zones, and rims. The core compositions display a range in Mg# (81–95) and are interpreted to be derived from the disaggregation of lithospheric mantle xenoliths and proto-kimberlite-related megacrysts. The Tongo olivine rims, interpreted to be primary magmatic crystallisation products, have similar compositions from various locations within the cluster whereas the Koidu samples display a range in rim compositions (Mg# 87–89) from different locations within the cluster. The average Koidu rim compositions display a strong positive correlation with the average core compositions, consistent with the trend formed by kimberlites worldwide and indicative of a strong control by melt-lithosphere interaction on melt compositions. Previously, it has been shown that the Mg# of olivine rim’s negatively correlates with the abundance of groundmass phlogopite (± oxide minerals) in kimberlites. However, the Koidu and Tongo kimberlites are exceptionally phlogopite-rich given their olivine Mg#, fall outside of the worldwide kimberlite array and have olivine compositions and phlogopite abundances like some cratonic lamproites. This leads us to suggest that Koidu and Tongo represent a rare style of highly micaceous kimberlite magmatism, not previously reported in other cratonic regions, and are genetically linked to the assimilation of K2O-rich, metasomatic mantle lithologies. We further suggest that the K2O content, reflected by groundmass phlogopite abundances, of worldwide kimberlite and cratonic lamproite parent magmas ascending to the surface may be related to assimilation of craton-specific styles of metasomatic lithologies in the SCLM.


Viljoen, A., Howarth, G. H., Giuliani, A., Fitzpayne, A. & Costin, G. (2022). Correlations between olivine composition and groundmass mineralogy in Sierra Leone kimberlites provide constraints on craton-specific melt-lithosphere interactions. LITHOS. Elsevier B.V. 430–431, 106846.

Geophysical Research Letters: Autocorrelation R2 on Mars

Sizhuang Deng and Alan Levander


Plain Language Summary

The subsurface structures of Earth are imaged by the detailed analysis of seismic data recorded by thousands of stations deployed on Earth’s surface. The InSight mission landed a seismograph on Mars which was deployed at the end of 2018 to investigate the planet’s interior structure and dynamic evolution. In this study, we preprocessed the continuous vertical-component seismic data, and by autocorrelation retrieved a Rayleigh wave, one class of seismic surface wave, that orbits Mars. Rayleigh wave group velocities between 115 and 200s period were measured from the observed Mars orbiting Rayleigh waves. Synthetic seismograms were calculated using current estimates of the velocity structure of Mars for comparisons to the observation. The spherically symmetric model was updated with a Monte Carlo algorithm, an inversion method that randomly perturbs the velocity model and determines the model that best matches the Mars orbiting surface waves through trial and error. An S-wave low-velocity zone is observed to the depth of ~400km beneath the Martian surface, consistent with other InSight seismic observations and velocity models measured from geophysical modeling and high-pressure laboratory experiments.