Estimating the carbon content of the deep mantle with Icelandic melt inclusions

Miller, William G. R. and Maclennan, John and Shorttle, Oliver and Gaetani, Glen A. and Le Roux, Vernique and Klein, Frieder (2019) Estimating the carbon content of the deep mantle with Icelandic melt inclusions. Earth and Planetary Science Letters, 523. ISSN 0012-821X DOI https://doi.org/10.1016/j.epsl.2019.07.002

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Abstract

Earth's carbon budget is central to our understanding of the long-term co-evolution of life and the planet. Direct observations of surface reservoirs allow for the detailed quantification of their carbon content. However, the carbon content of Earth's deep interior remains poorly constrained. Here we study olivine-hosted melt inclusions from two Icelandic eruptions, with those from the Miðfell eruption allowing us to investigate the carbon content of the deep mantle. Comparison with the previously studied Borgarhraun eruption highlights the presence of deep, plume-sourced mantle material within the Miðfell source region. Miðfell contains trace element-depleted melt inclusions undersaturated in CO2, which have high CO2/Ba () and CO2/Nb (), though some inclusions preserve even greater relative carbon enrichment. These observations allow us to reconstruct the CO2 content of the bulk Miðfell source as being . By identifying that Miðfell is a mixture of depleted and deep mantle components, we can estimate a CO2 content for the deep mantle component of ; a concentration that is over ten times higher than depleted MORB mantle estimates. Assuming that the deep mantle component identified in Miðfell is representative of a global reservoir, then with our new CO2 estimate and by considering a range of representative mantle fractions for this reservoir, we calculate that it contains up to 14 times more carbon than that of the atmosphere, oceans, and crust combined. Our result of elevated CO2/Ba and CO2/Nb ratios, and carbon enrichment support geochemical bulk Earth carbon models that call for the presence of carbon-rich deep mantle domains to balance Earth's relatively carbon-poor upper mantle and surface environment.

Item Type: Article
Uncontrolled Keywords: 2019AREP; IA75
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
12 - PhD
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 523
Identification Number: https://doi.org/10.1016/j.epsl.2019.07.002
Depositing User: Sarah Humbert
Date Deposited: 23 Jul 2019 14:20
Last Modified: 19 Jul 2020 00:03
URI: http://eprints.esc.cam.ac.uk/id/eprint/4512

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