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Sr isotope compositions are reported for 37 volcanic rocks from the Island of Stromboli and for 8 samples from the islands of Filicudi and Alicudi, Aeolian Arc, south Tyrrhenian Sea. The rocks cover the entire compositional range of the Aeolian volcanics which vary from calc-alkaline (CA) to high-K calc-alkaline (HKCA), shoshonitic (SHO) up to potassic series (KS). In the Island of Stromboli the Sr isotopic ratio ranges from 0.70519 to 0.70757 and increases regularly from the CA to HKCA and SHO, reaching the highest values in the KS volcanics. Significant variations are also observed within individual magmatic series, especially the KS. The Filicudi and Alicudi samples include typical CA basalts and basaltic andesites that display lower Sr isotopic ratios (0.70379–0.70538) than the Stromboli volcanics. The data indicate that fractional crystallization has been the leading process in the evolution of the HKCA and SHO series, although some samples show clear evidence of mixing with CA and KS magmas. The KS volcanics display a range of isotopic composition which is negatively correlated with Sr abundance, indicating processes of crustal assimilation. The overall Sr isotopic variations in the Stromboli rocks and the positive relationship with K enrichment are interpreted as indicating either the genesis of parent magmas of the different series in a heterogeneous mantle source or formation by processes of crystal fractionation associated with assimilation and mixing in a periodically refilled and tapped deep magma chamber.

The Sabatini Volcanic District (SVD) is a large volcanic field characterised by the lack of any major volcanic center. Its activity, spread over a wide area, started at 0.6 Ma and developed through five main phases, during which several calderas and the Bracciano lake volcano-tectonic depression were formed. All the volcanic rocks belong to the Roman-type ultrapotassic series (HKS), ranging from leucite tephrites to leucite and hauyne phonolites. Although the major- and compatible-element contents indicate a single series of evolution, there are differences in the incompatible trace-element abundances. A high-Ba series (HBaS) has been distinguished from a low-Ba series (LBaS), with the former also enriched in all other incompatible elements (e.g., REE, Nb, Zr, Th) except Rb. The HBaS rocks are plagioclase-free, leucite-bearing lavas and were abundantly outpoured from the Bracciano volcanoes during the third and fifth phase of activity. Plagioclase- and phlogopite-bearing rocks constitute the LBaS and were erupted during the other phases generally from smaller and eccentric volcanic centers. The initial 87 Sr/ 86 Sr values are higher in the HBaS rocks and do not vary significantly with magma evolution (0.71047–0.71080), but cover a wider range in the LBaS rocks (0.70944–0.71038), with the lowest Sr isotope ratios occurring in the least evolved lavas. The higher Ca content in the olivine and Ti and Al IV in the clinopyroxene, and the lower ulvospinel content of the Ti-magnetites of the HBaS rocks suggest an evolution at lower pressure and higher temperature for this magma. The observed petrologic characteristics suggest that the HBaS magma evolved at lower depths by processes of refilling, tapping, fractionation and probably assimilation (RTFA), where the crystallisation rate of clinopyroxene+leucite±olivine dominates over the input rate of the fresh magma. The LBaS magma evolved at slightly higher pressure, in separate and small magma bodies, by fractional crystallisation of clinopyroxene+plagioclase±phlogopite±olivine that was often associated with crustal assimilation (AFC). It has been suggested that RTFA processes with high input rate/crystallisation rate ratios could also be responsible for the differentiation between the HBaS and LBaS. The different processes of evolution undergone by the HBaS and LBaS could have been related to the different volumes of magma rising from the source.