ORIGIN AND DIFFERENTIATION OF RECENT BASALTIC MAGMAS FROM MOUNT-ETNA

One hundred and fifty samples of recent Na-alkalic lavas from the sout h-eastern flank of Mt. Etna, dating from about 5,000 years B.P. to 188 6 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 f elsic end than previously known. Chondrite-normalized REE patterns of the least differentiated samples show LREE enrichment and HREE depleti on; trace element compositions suggest that Etnean products are simila r 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 sugg est that processes other than simple crystal fractionation are, in par t, responsible for the variation of the analyzed sequence. In fact, RT F processes with successive influxes of mafic melts, each having disti nct, slightly different geochemical and isotopic features, into reserv oirs of variously differentiated magmas, may explain the overall obser ved data. The source region for Recent Mongibello lavas is located in the mantle, isotopically zoned, and Rb-depleted with respect to the Bu lk Earth composition. Model and experimental data conform well with a low degree (< 5%) modal melting of a garnet Iherzolite source, deplete d by an earlier melting event with respect to primitive mantle composi tion.