Abstract

Abstract The fate of carbonate-rich sediments recycled at destructive plate margins is a key issue for constraining the budget of deep CO2 supplied to the atmosphere by volcanism. Experimental studies have demonstrated that metasomatic melts can be generated by partial melting of subducted carbonate-pelitic sediments, but signatures of the involvement of such components in erupted magmas are more elusive. We have made new U-Th disequilibria, Sr-Nd-Pb isotope, and high-precision δ238U analyses on lavas from Mount Vesuvius (Italy) and show that their measured 238U excesses require a mantle source affected by the addition of U-rich carbonated melts, generated by partial melting of subducted calcareous sediments in the presence of residual epidote. Accordingly, we argue that the occurrence of 238U excesses in “sediment-dominated” arc magmas represents diagnostic evidence of addition of carbonate sediments via subduction, hence providing constraints on deep carbon cycling within Earth. Our quantitative enrichment model, combined with published experimental results, allows us to estimate a resulting flux of 0.15–0.8 Mt/yr CO2 from the subducted carbonates to the mantle source of Mount Vesuvius.

Highlights

  • The fate of carbonate-rich sediments recycled at destructive plate margins is a key issue for al., 2015) have shown that subducted carbonconstraining the budget of deep CO2 supplied to the atmosphere by volcanism

  • The oceanic to directly quantifying the origin of CO2 emis- occurrence of crustal limestone assimilation en slab is subducted into the mantle, carrying both sions from volcanoes, with major consequences route to the surface, which may modify the combasaltic oceanic crust and overlying sediments. for atmospheric fluxes (Burton et al, 2013)

  • Position of the erupted magmas, overprinting. Part of this subducted material is released their contribution to subduction zone magmas is some of the geochemical and isotopic signatures at depth, affecting the mantle wedge above the not necessarily distinctive in many traditionally inherited from the mantle source

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Summary

Introduction

The fate of carbonate-rich sediments recycled at destructive plate margins is a key issue for al., 2015) have shown that subducted carbonconstraining the budget of deep CO2 supplied to the atmosphere by volcanism. Our data indicate instead that subducted carbonate-rich sediment melts (MMC) have an important role in the chemical and isotopic composition of Vesuvius lavas, and Italian magmatism more generally (e.g., Avanzinelli et al, 2008; Conticelli et al, 2015), resulting in significant “subduction-derived” CO2 fluxes (see Frezzotti et al, 2009).

Results
Conclusion

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