Earlier alkaline and transitional magmatic pulsation of Mt Etna volcano

The observation of glass inclusions with alkalic and transitional compositions in single olivine crystals from Aci Castello hyaloclastites indicates that small volumes of alkalic melts preceded tholeiite eruptions during the onset of Mt Etna volcanism. The gradual shift in composition from alkalic to transitional melts is explained by simple partial melting of a compositionally uniform source, with the degree of melting increasing by a factor of 3-4 during this early melting process. Such variation controls both the chemical and mineralogical signatures of emitted lavas. The source shows trace-element and isotopic signatures which may be representative of a HIMU-type plume for Etnean lavas.