Volcanism, calderas and magmas of the Alicudi composite volcano (western Aeolian archipelago)

The Alicudi composite volcano (western Aeolian archipelago) was constructed between c. 106 and 28 ka by lava flows, domes and strombolian scoriae erupted during six Eruptive Epochs, interrupted by periods of dormancy and three caldera-type collapses in the summit area. Marine Isotope Stage (MIS) 5a (81 ka) terrace deposits and widespread Brown Tuffs of external origin are recognized and provide important marker beds for regional stratigraphic correlations. Volcanism was of central type, under control of the summit caldera collapses with negligible influence of regional tectonic trends. Alicudi rocks are basaltic to high-K andesitic and have the most primitive petrological compositions (high MgO, Ni, Cr contents), the lowest Sr-O and the highest Nd-He isotope ratios (87Sr/86Sr 1/4 0.70352 to 0.70410; 143Nd/144Nd 1/4 0.51289 to 0.51279; δ18O = + 5.0 to 5.6; 3He/4He-R/Ra 1/4 c. 6.5 to 7.1) over the entire Aeolian archipelago. Their composition and variation through time are the result of polybaric crystal-liquid fractionation of parental calc-alkaline basalts to give basaltic andesitic and andesitic derivative melts. These underwent crustal assimilation during ascent, with basalts being contaminated more strongly than andesitic magmas. Sr-Nd-Pb isotopes suggest source metasomatic modification by fluids from an oceanic-type slab, with a minor role for subducted sediments. © The Geological Society of London 2013.