Origin and differentiation of recent basaltic magmas from Mount Etna

Abstract

One hundred and fifty samples of recent Na-alkalic lavas from the south-eastern flank of Mt. Etna, dating from about 5,000 years B.P. to 1886 were analyzed. They grade in time from more acid to more basic lavas, and show an overall range of variation much larger toward the more felsic end than previously known. Chondrite-normalized REE patterns of the least differentiated samples show LREE enrichment and HREE depletion; trace dement compositions suggest that Etnean products are similar to WPB, with a weak CAB signature. Sr-isotope ratios ranging from 0.70332 to 0.70355, vary even within samples from the same eruption, and generally tend to increase with time in historic lavas. Our data suggest that processes other than simple crystal fractionation are, in part, responsible for the variation of the analyzed sequence. In fact, RTF processes with successive influxes of mafic melts, each having distinct, slightly different geochemical and isotopic features, into reservoirs of variously differentiated magmas, may explain the overall observed data. The source region for Recent Mongibello lavas is located in the mantle, isotopically zoned, and Rb-depleted with respect to the Bulk Earth composition. Model and experimental data conform well with a low degree (< 5%) modal melting of a garnet lherzolite source, depleted by an earlier melting event with respect to primitive mantle composition.