The global melt inclusion C/Ba array: mantle variability, melting process, or degassing?

Matthews, Shorttle, Maclennan, Rudge, GCA 293, 525-543 (2021). doi: 10.1016/j.gca.2020.09.030

In this paper we present new melt inclusion data from four Icelandic eruptions: Háleyjabunga, Stapafell, Berserkjahraun, and Heilagsdalsfjall. We used Secondary Ion Mass Spectrometry, Electron Microprobe Analysis, and Raman Analysis, to fully characterise the inclusions’ major, trace, and volatile element compositions. We then compiled this new data with previously published data from Iceland and the rest of the world.

The ratio of C/Ba in melt inclusions and submarine glasses has been used to estimate the magnitude and heterogeneity in carbon content of the mantle. Though mantle carbon contents are thought to be low (generally), the mantle is a significant reservoir of carbon on a planetary scale, and is likely to help regulate the surface carbon cycle on planetary timescales. It also has first order control on where magmas can form in the mantle, and ultimately make their way to the surface.

We find there’s a strong covariation of C/Ba ratio with indexes of geochemical enrichment, often thought to track with the contribution of recycled components to magma genesis. However, we show that this is likely a consequence of crustal processing rather than being a property of the mantle. This study lays the groundwork for future work in quantifying the small-scale carbon heterogeneity we think is very likely to be present in Earth’s mantle.

The image is Figure 5 from the manuscript, and shows off our new data alongside data presented in many other studies.

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