Magmagenesis at Soufriere volcano St Vincent, Lesser Antilles Arc
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Abstract
Soufriere volcano of St Vincent (<0.6 Ma) is composed of basalts and basaltic andesites, the most mafic of which (mg-number 75) may be representative of the parental magmas of the calc-alkaline suites of the Lesser Antilles arc. Parental, possibly primary, magmas at Soufriere had MgO ∼12.5 wt % and were probably nepheline-normative. They last equilibrated with mantle at ∼17 kbar pressure, at temperatures of around 1130°C and f(O2) exceeding FMQ (fayalite–magnetite–quartz) + 1. They fractionated, along several liquid lines of descent, through to basaltic andesites and rarer andesites over a range of crustal pressures (5–10 kbar) and temperatures (1000–1100°C), separating initially olivine + Cr-spinel + clinopyroxene + plagioclase ± titanomagnetite and then clinopyroxene + plagioclase + titanomagnetite + orthopyroxene assemblages. The total amount of crystallization was some 76 wt %. Amphibole was apparently not a fractionating phase. Sr and Nd isotopic and trace element systematics show no evidence for significant crustal assimilation. There is conflicting evidence as to the pre-eruptive water contents of Soufriere magmas; compositions of clinopyroxene phenocrysts and melt inclusions suggest H2O >3 wt %, whereas various projections onto phase diagrams are more consistent with relatively anhydrous magmas. Primary magmas at Soufriere were generated by around 15% melting of mid-ocean ridge basalt type mantle sources which had been modified by addition of fluids released from the slab containing contributions from subducted sediments and mafic crust.
Publication type | Article |
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Publication Subtype | Journal Article |
Title | Magmagenesis at Soufriere volcano St Vincent, Lesser Antilles Arc |
Series title | Journal of Petrology |
DOI | 10.1093/petroj/39.10.1721 |
Volume | 39 |
Issue | 10 |
Year Published | 1998 |
Language | English |
Publisher | Oxford Academic |
Description | 44 p. |
First page | 1721 |
Last page | 1764 |
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