Melt evolution beneath thick lithosphere: A magmatic inclusions study of La Palma, Canary Islands

Volcanism in the Canary Islands is notable for its highly alkalic character even in the shield building lavas of the currently most active island, La Palma. In order to understand better the processes responsible for this alkalic end of the compositional spectrum of ocean island basalts (OIB), we have studied primary magmatic inclusions in olivine and clinopyroxene from La Palma. The investigated primary melt and fluid inclusions are hosted by olivine and clinopyroxene from lavas of two ∼700-ka, continuous stratigraphic sections in the Fagundo and Izcagua barrancos of the main shield volcano Taburiente. Lavas from the two barrancos show contrasting whole-rock compositions: Izcaqua lavas are highly alkalic or “basanitic”, typical of La Palma lavas in general, whilst the Fagundo lavas are characterised by more silica-rich, “transitional”, compositions. Although whole-rock compositions of the lavas from the two barrancos show different degrees of silica undersaturation, they show a similar range of elemental abundances such as MgO. In contrast, the Fagundo melt inclusions show a wider range, to more mafic compositions, than those from the Izcagua samples. This is in keeping with more variable partial homogenisation temperatures and host mineral compositions in the Fagundo samples, which are also generally higher (1130–1260 °C) and more primitive (Fo 76–87) than in the Izcagua suite. Indeed, the Izcagua melt inclusions are hosted in relatively evolved liquidus mineral assemblages (Fo