Primary magmas, fractionation modelling and mantle source of Etnean lavas

Mt. Etna is the highest European Volcano and one of the most active in the world. For this reason the investigation of the deep and shallow feeding system of Mt. Etna, and subsequently of his mantle source could give us some information about the eruptive style thus helping to predict future volcanic events. In this respect the complete evolution of Mt. Etna magmatism was considered performing a detailed sampling from Tholeiitic to Recent Mongibello periods. Backward mass balance fractionations were used to reconstruct the primary composition of Etnean magmas and get some inferences on the petrological composition of their mantle sources. The Tholeiitic suite did not necessitate a backward reconstruction for the presence of real primary un-fractionated compositions. To reach the most evolved terms is hypothesized the involvement of 27% Ol, 14% Cpx, 29% Opx, 15% Plg and 15% Cr-Sp for a total amount of 53.1% of gabbroic material The least differentiated products for each alkaline period were identified and about 17 to 19% of a solid assemblage made up of Ol (87 to 100%) and Cpx (up to 13%) was added to re-equilibrate the basalts with mantle olivine (Fo87). A further subtraction of an average 23.3% of a solid assemblage constituted by Ol (7-18%), Cpx (26-55%) and Plag (21-48%) is needed to get to the most differentiated erupted lavas.Taking into account the volume of the erupted magmas this modeling can be used to evaluate the quantity of material intruded below the volcano edifice. On average an estimation of about 40% of material should be considered beneath it. Thus if according to Neri and Rossi (1992) the whole volcano edifice amounts to about 370 km3, about 150 km3 of magma should be left behind from the magma on its way from the mantle to the surface. Calculated major element compositions of the primary magmas are well comparable with those obtained by melt inclusions study, while trace element patterns fit well with those reported in the literature. These compositions are also similar to those found in the Iblean Plateau Although Etnean alkaline lavas appear enriched in K, Rb, Th and U and depleted in Ti, Y and Yb. Thus partial melting models were developed for each Etnean magmatic period, based on a mantle composition similar to that of the nearby Iblean lithosphere. Results indicate two different sources for Tholeiitic and Alkaline suites analogously to the modeling developed by Beccaluva et al. (1998). Tholeiitic magmas can be reproduced by about 17% of an amphibole-bearing peridotite source, while alkaline magmas can be reproduced by melting of about 7% an amphibole-phlogopite-bearing peridotite source. Our result are in agreement with those recently advanced by Correale et al. (2014) indicating a large similarity between Mt. Etna and Mt. Iblei mantle sources. Neri and Rossi (1992) Quaderni di geofisica – Istituto nazionale di Geofisica e Vulcanologia 20 Beccaluva et al. (1998) J. Petrology 39, 1547-1576. Correale et al. (2014) Lithos, 184-187: 243-258.