The mineral chemistry and origin of xenoliths from the lavas of Anjouan, Comores Archipelago, Western Indian Ocean

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Abstract

Mineralogical data for xenoliths occurring as inclusions in the fissure erupted alkali basalts and the basanitic tuffs of Anjouan reveal three xenolith suites: 1) the lherzolites, 2) the dunites and wehrlites, 3) the gabbros and syenites. The " dunite-wehrlite " suite and the gabbro suite are shown to represent high-level cumulate sequences resulting from ankaramitic fractionation of the hy-normative shield-building lavas and cotecictic fractionation of the alkali basalt lavas respectively, whilst the syenitic xenoliths represent evolved high-level intrusions. Mineralogical and rare earth element (REE) data indicate that the most likely origin for the spinel lherzolite xenoliths is by extraction of a basaltic phase from spinel peridotite, leaving a light REE-poor spinel lherzolite residuum. REE models, constructed using model peridotite assemblages, imply that the hy-normative basalt lavas may be derived by partial melting of spinel peridotite at pressures of <20-25 kb leaving a residual lherzolite, and that the alkali basalt and basanite melts are formed by small degrees of melting of a garnet-peridotite source at pressures of >20-25 kb. The spinel lherzolite source for the hy-normative basalts has been accidentally sampled during explosive eruption of the alkali basalt and basanite magmas.

Original languageEnglish
Pages (from-to)91-107
Number of pages17
JournalContributions to Mineralogy and Petrology
Volume64
Issue number1
DOIs
Publication statusPublished - Jan 1977

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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