Light elements, volatiles, and stable isotopes in basaltic melt inclusions from Grenada, Lesser Antilles: Inferences for magma genesis

Abstract

[1] 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 dD, d11 B and d 7Li determinations of melt inclusions hosted in olivines (Fo 86-91 ) from picritic scoriae. The major element compositions of melt inclusions encompass those of Grenada basalts. Their H 2 O 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 H 2 O contents are associated with strongly negative values of dD (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 d 7 Li and d 11 B, 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 d 11 B, high-Cl, Li-poor fluids derived from the early dehydration of serpentinized peridotite above the slab beneath Grenada.

Geochemistry and geochronology of Grenada and Union islands, Lesser Antilles: The case for mixing between two magma series generated from distinct sources

“…• There are only a third as many analyses of C-series (26) as M-series 75analyses in our database, suggesting the Grenadian crust consists dominantly of M-series material. Furthermore, xenoliths we analyzed have predominately M-series isotopic compositions, and most of the melt inclusions analyzed by Bouvier et al (2010) appear to be M-series related. (It could be argued that the melt inclusions are M series only because the host lava is also, but the inclusions display considerable heterogeneity and appear largely unrelated to the host lava.)…”

“…Where the major-element compositions of samples in this range are ambiguous as to which series a sample belongs, we have used isotope ratios as additional criteria (see below). The melt inclusions analyzed by Bouvier et al (2010) plot mainly within the M-series trends and are distinct from the C series, which is not surprising since the Queen's Park scoria cone, from which these samples were taken, consists of M-series picritic basalt (our sample from this site is GDA008, the majorelement composition of which was previously reported by Devine, 1995). However, a few of the inclusions have CaO contents well above those seen in M-series lavas, and in some cases above those of the C series, at comparable MgO.…”

“…However, the compositions considered in those studies were richer in CaO (>15%), had CaO/Al 2 O 3 > 1, and were generally poorer in silica than the C series considered here. Sorbadere et al (2012) considered the compositions of MgO-rich melt inclusions in nepheline-normative arc magmas, including those from Grenada analyzed by Bouvier et al (2010), and they found that their compositions defined trends suggestive of mixing between melts generated by partial melting of peridotite-and amphibole-bearing, clinopyroxene-rich lithologies. This is illustrated in Figure 19 in two ternary projections in which compositions are recast into the system CaO-MgO-Al 2 O 3 -SiO 2 (CMAS) using the method of O'Hara (1968).…”

In situ study of the fractionation of hydrogen isotopes between aluminosilicate melts and coexisting aqueous fluids at high pressure and high temperature – Implications for the δD in magmatic processes

“…The δD-values of melt inclusions in phenocrysts from subduction settings (Shaw et al, 2008;Bouvier et al, 2010;Métrich and Deloule, 2014) might be used to constrain the δD-value of slabderived fluids provided that the D/H fractionation factor, α fluid-melt , is known. For example Shaw et al (2008) suggested that the average δD-value of melt inclusions from the Mariana arc (−34h) reflects the δD-value of the aqueous fluids released by the subducting slab, and thus might be used to determine the extent of slab dehydration.…”

Contrasting partition behavior of F and Cl during hydrous mantle melting: implications for Cl/F signature in arc magmas

“…Straub et al 2004;Le Voyer et al 2008;Sadofsky et al 2008;Bouvier et al 2010;Sorbadere et al 2011). The composition of the metasomatic agent is usually calculated from mass balance assuming a mixing between the depleted mantle (DMM) and this agent, either a slab aqueous fluid or a slab melt (e.g.…”