Light elements, volatiles, and stable isotopes in basaltic melt inclusions from Grenada, Lesser Antilles: Inferences for magma genesis
Résumé
Grenada Island is located at the southern end of the Lesser Antilles. Grenada lavas display a large range in compositions which includes picrites, representing the parental melt of all Grenada suites. We present here an extensive study of major, light and volatile elements combined with δD, δ11B and δ7Li determinations of melt inclusions hosted in olivines (Fo86–91) from picritic scoriae. The major element compositions of melt inclusions encompass those of Grenada basalts. Their H2O contents typically range from 0.2 to 4.1 wt% (one value at 6.4 wt%). Such extreme range stands in contrast with typical arc magmas for a single volcanic center. The high H2O contents are associated with strongly negative values of δD (on average −140‰). Melt inclusions display a wide range in B (1.7–47 ppm) and Li (1.1–12 ppm) contents as well as in δ7Li and δ11B, which vary from −24 to 8.2‰ and from −20 to 8.9‰, respectively. Both B and Li compositions of Grenada melt inclusions suggest (i) the involvement of dehydration fluids or hydrous silicate melts derived from buried carbonate‐bearing sediments, (ii) the contribution of aqueous fluids generated during the dehydration of hydrothermally altered oceanic crust, and (iii) melting of a mantle metasomatized by the addition of high δ11B, high‐Cl, Li‐poor fluids derived from the early dehydration of serpentinized peridotite above the slab beneath Grenada.
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