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An increase in the mass eruption rate at Mount Etna since 1971 is coupled with a shift in Sr-Nd isotope ratios, enhancing a trend that has characterized the volcano since its earliest stages of activity. After 1971, rapid geochemical variations provide evidence for mixing and mingling of magma batches with different geochemical characteristics in a highly dynamic regime. Magma mixing is evidenced by changes in the Sr isotope composition of the erupted products as well as by isotopic disequilibrium between pyroxene phenocrysts and the whole rocks. The early appearance of clinopyroxene on the liquidus of the magmas combined with thermobarometric estimates suggest that clinopyroxene can be used as a tracer of polybaric crystallization processes that take place mostly at mantle depths, along equilibrium liquid lines of descent from parental magmas with water contents between 1 and 3% by weight. Rising magmas seem to have ponded at the crust-mantle boundary for short periods of time, from where they started to rise along a steeper dP/dT gradient, greater than that to the high-velocity crustal body seismically imaged at ∼10 km beneath the volcano summit. Sr isotope disequilibrium between clinopyroxene phenocrysts and the whole rocks provides evidence that crystal mushes at different depths may be incorporated into subsequent magma batches affecting both the crystal size distribution and isotopic composition of clinopyroxene.

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