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Journal of Petrology Advance Access originally published online on July 7, 2008
Journal of Petrology 2008 49(8):1427-1448; doi:10.1093/petrology/egn031
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© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Slab-Derived Fluids in the Magma Sources of St. Vincent (Lesser Antilles Arc): Volatile and Light Element Imprints

A.-S. Bouvier1,*, N. Métrich2 and E. Deloule1

1Centre De Recherche Pétrographiques Et Géochimiques, Nancy-Université, CNRS 54501 Vandoeuvre-Les-Nancy, France
2Laboratoire Pierre Süe, CNRS-CEA, Ce-Saclay, 91191 Gif-Sur-Yvette Cedex, France

RECEIVED DECEMBER 11, 2007; ACCEPTED MAY 6, 2008


  Abstract

It is generally accepted that the parental magmas of the Lesser Antilles arc were generated by partial melting of a mid-ocean ridge basalt (MORB)-type mantle source modified by slab-derived components. To determine the nature of these components, the H2O, S, Cl, F, Li and B contents and {delta}7Li, {delta}11B, {delta}18O and {delta}34S compositions were systematically determined in olivine-hosted melt inclusions from St. Vincent (southern part of the arc). Both the geochemical and isotopic data define a broad compositional spectrum. On the whole, the melt inclusions have basaltic to CaO-rich (>15·0 wt %), SiO2-poor (< 45·7 wt %) compositions. Most of the entrapped melts result from ~10–20% batch partial melting of a MORB-type mantle source modified initially by dehydration fluids with low solute contents and a seawater-like chemical signature. As a result, the melt inclusions are enriched in B, Cl and H2O compared with MORB and have {delta}11B up to + 15{per thousand}, {delta}34S of ~2{per thousand} and {delta}18O down to + 3{per thousand}. In contrast, some others record initial magmatic heterogeneities that require input of fluids derived from (1) the dehydration of altered oceanic crust in agreement with the selective B enrichment (up to 53 ppm) in the melt and negative lithium isotopic compositions, and (2) the dehydration of sediments resulting in distinctive {delta}11B and {delta}34S (down to –20{per thousand} and –8{per thousand}, respectively) and high Li contents in the melts. The CaO-rich melt inclusions cannot be distinguished from the others on the basis of their isotopic signatures. They possibly reflect magma interactions with CaO-rich, amphibole-bearing lithologies. Combination of our results with literature experimental data leads to the conclusion that St. Vincent basaltic melt inclusions—whose water content varies from 2·2 to 3·6 wt %—represent magmas derived from a rather limited portion of the mantle wedge, by partial melting at between 13 and 14·5 kbar and a restricted temperature range (1220–1190°C).

KEY WORDS: Lesser Antilles arc; subduction; melt inclusions; volatiles; stable isotopes

*Corresponding author. Fax: +33 3 83 51 17 98. E-mail: abouvier{at}crpg.cnrs-nancy.fr


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