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| Titel |
Carbonate-derived CO2 purging magma at depth: constraints from the O-isotope geochemistry of Somma-Vesuvius mafic products |
| VerfasserIn |
Luigi Dallai, Raffaello Cioni, Chiara Boschi, Claudia D'Oriano |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053730
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| Zusammenfassung |
| It has been increasingly clear that carbonate assimilation by mafic magmas occurs in
volcanic systems set in carbonate basement. Experimental petrology predicts that
carbonate/melt interaction modifies the chemical characteristics of the evolved
magmas (Iacono Marziano et al., 2007; Freda et al., 2008; Mollo et al 2010) and
drive their compositions toward silica-undersatured end-members. The effects of
carbonate addition onto magma dynamics is poorly constrained, and the inevitable
occurrence of CO2 degassing due to magma/heat/carbonate interaction has the
potential to change the overall volatile solubility of the magma, thereby justifying the
ability of magmas to rapidly rise and explosively erupt to the surface. Due to the
large difference in 18O/16O ratios between sedimentary carbonate (formed in a
shallow crustal environment) and mafic magmas (mantle domain) oxygen isotope
systematic likely represents the most powerful tool to trace carbonate addition to
near-primary melts (e.g. Dallai et al., 2004) particularly into volcanic products, as
their high cooling rate prevents subsolidus requilibration and allows pre-eruptive
O-isotope composition to be preserved. Based on simple mass balance calculations the
amount of carbonate addition can be estimated and further constrained by melt
inclusion compositions. The combined use of O-isotope and REE data of mafic
phenocrysts(ante-crysts)from major eruptions at Mt. Vesuvius and the chemistry of their melt
inclusions allowed bulk carbonate assimilation (physical digestion) vs. CO2/melt interaction
to be resolved. Data are compatible with the hypothesis of an extensive flux of
CO2-rich fluids derived from magma-carbonate interaction (thermal decomposition and
carbonate assimilation) passed through the magma in the roots of the volcanic edifice.
This flux is responsible for the d18O values of primary Mt. Vesuvius melts before
extensive carbonate interaction occurred during magma stalling in shallow crustal
reservoirs.
Refs. Dallai L. et al., 2004. CMP 148, 247-263. Freda C. et al., 2008. Lithos 101,
397-415. Iacono Marziano G., et al., 2007. CMP 155, 719-738. Mollo S. et al., 2010. Lithos
114, 503–514. |
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