A two-component mantle source feeding Mt. Etna magmatism: Insights from the geochemistry of primitive magmas

Themajor elements, trace elements and Sr and Nd isotopes of selected Etnean primitive rocks (b15 ky BP) were
studied in order to characterize their mantle source. The noble-gas geochemistry of fluid inclusions in minerals
fromthe same lavaswas also investigated. Themajor element compositions ofwhole rocks and minerals showed
that these products are among the most primitive atMt. Etna, comprising 6.3–17.5 wt.% MgO. The variable LREE
(Light Rare Earth Elements) enrichment relative to MORB (Mid-Ocean Ridge Basalt) (Lan/Ybn = 11–26), togetherwith
the patterns of certain trace-element ratios (i.e., Ce/Yb versus Zr/Nb and Th/Y versus La/Yb), can be attributed
to varying degrees of melting of a common mantle source. Numerical simulations performed with the
MELTS program allowed the melting percentages associated with each product to be estimated. This led us to recalculate
the hypothetical parental trace-element content of the Etneanmantle source, whichwas common to all
of the investigated rocks. The characteristics of the Sr, Nd and He isotopes confirmed the primitive nature of the
rocks,with themost-depleted and primitive lava being that ofMt. Spagnolo (SPA; 143Nd/144Nd = 0.512908 87Sr/
86Sr = 0.703317–0.703325 and 3He/4He = 7.6 Ra), and highlighted the similarity of the mantle sources feeding
the volcanic activity of Mt. Etna and the Hyblean Plateau (a region to the south of Mt. Etna and characterized by
oldermagmatismthan Mt. Etna). The coupling of noble gases and trace elements suggests an origin for the investigated
Etnean lavas from melting of a Hyblean-like mantle, consisting of a two-component source where a
peridotitic matrix is veined by 10% pyroxenite. A variable degree of mantle contamination by crustal-like fluids,
probably related to subduction, is proposed to explain the higher Sr-isotope and lowerNd-isotope values in some
rocks (143Nd/144Nd up to 0.512865 and 87Sr/86Sr up to 0.703707). This process probably occurred in the source
prior tomagma generation, refertilizing some portions of themantle. Accordingly, the estimated degree of melting
responsible for each magma appears to be related to its 87Sr/86Sr enrichment. In contrast, the decoupling
between 3He/4He and 87Sr/86Sr ratios requires the occurrence in the crustal reservoirs of further processes capable
of shifting the He isotope ratio towards slightly more radiogenic values, such as magma aging or a contribution
of shallow fluid. Therefore, different residence times in the Etnean reservoir and/or various rates of magma
ascent could be key parameters for preserving the original He isotope marker of the Etnean mantle source.