Mount Etna and the 1971 eruption - The 1971 Etna eruption: petrography of the lavas

Abstract

Most petrologists who have worked on Mt Etna have been surprised by the rather uniform character of its lavas (Lacroix 1908; Washington et al. 1926; Di Franco 1930). Except for a slight differentiation from alkali basalts to trachyandesites in the ancient Trifoglietto caldera, almost all the products forming this huge complex edifice have a tephritic basalt composition. They are usually porphyritic, with phenocrysts of calcic plagioclase (zoned from An 85 to An 40), augite, olivine and titaniferous magnetite. All these minerals, except olivine, are present in the groundmass, which also shows notable amounts of cryptocrystalline sanidine (about 10 %) and nepheline (about 5% ), these being determined by X-ray diffraction (Tanguy 1966). This uniformity in the petrochemistry of Mt Etna is interpreted by Rittmann as resulting from the absence of an intermediate magmatic reservoir, in relation with the tectonic history of the volcano (Rittmann 1963, 1973).