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Article Dans Une Revue Geochimica et Cosmochimica Acta Année : 2024

High CO2 in the mantle source of ocean island basanites

Résumé

Some of the most CO2-rich magmas on Earth are erupted by intraplate ocean island volcanoes. Here, we characterise olivine-hosted melt inclusions from recent (< 10 ky) basanitic tephra erupted by Fogo, the only active volcano of the Cape Verde Archipelago in the eastern Atlantic Ocean. We determine H2O, S, Cl, F in glassy melt inclusions and recalculate the total (glass+shrinkage bubbles) CO2 budget by three independent methodologies. We find that the Fogo parental basanite, entrapped as melt inclusion in forsterite-rich (Fo80-85) olivines, contains up to ∼2.1 wt% CO2, 3-47% of which is partitioned in the shrinkage bubbles. This CO2 content is among the highest ever measured in melt inclusions in OIBs. In combination with ∼2 wt.% H2O content, our data constrain an entrapment pressure range for the most CO2-rich melt inclusion of 648-1430 MPa, with a most conservative estimate at 773-1020 MPa. Our results therefore suggest the parental Fogo melt is stored in the lithospheric mantle at minimum depths of ∼27 to ∼36 km, and then injected into a vertically stacked magma ponding system. Overall, our results corroborate previous indications for a CO2-rich nature of alkaline ocean island volcanism. We propose that the Fogo basanitic melt forms by low degrees of melting (F=0.06-0.07) of a carbon-enriched mantle source, containing up to 355-414 ppm C. If global OIB melts are dominantly as carbon-rich as our Fogo results suggest, then OIB volcanism may cumulatively outgas as high as ∼16-21 Tg of carbon yearly, hence substantially contributing to the global deep carbon cycle.
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insu-04431773 , version 1 (01-02-2024)

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Francesco Maria Lo Forte, Federica Schiavi, Estelle F. Rose-Koga, Silvio G Rotolo, Maximilien Verdier-Paoletti, et al.. High CO2 in the mantle source of ocean island basanites. Geochimica et Cosmochimica Acta, 2024, ⟨10.1016/j.gca.2024.01.016⟩. ⟨insu-04431773⟩
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