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Arrival of extremely volatile-rich high-Mg magmas changes explosivity of Mount Etna

¹ Australian Research Council Centre of Excellence in Ore Deposits and School of Earth Sciences, University of Tasmania, Hobart, Tasmania 7001, Australia
² Istituto Nazionale di Geofisica e Vulcanologia-Sezione di Pisa, Via della Faggiola 32 Pisa 56126, Italy
³ Laboratoire Pierre Sue, Centre National de la Recherche Scientifique-Commissariat à l'Energie Atomique, CE-Saclay, 91191 Gif sur Yvette, France
⁴ Max-Planck-Institut für Chemie, Postfach 3060, 55020 Mainz, Germany, and Vernadsky Institute of Geochemistry, Moscow 117975, Russia
⁵ Max-Planck-Institut für Chemie, Postfach 3060, 55020 Mainz, Germany, and Institute of Geology and Mineralogy SB RAS, Novosibirsk 630090, Russia
⁶ GeoForschungsZentrum Potsdam, Telegrafenberg B 120, D-14473 Potsdam, Germany

The volcanic hazard potential of Mount Etna volcano is currently nourished by long-lasting, powerful eruptions of basaltic magmas coupled with increased seismicity and ground deformation, and the world's largest discharge of volcanic gases. The current evolutionary cycle of Mount Etna activity is consistent with subduction-related chemical modifications of the mantle source. Arrival of a new mantle-derived magma batch beneath the volcano has been hypothesized, but is still elusive among the erupted products. Here we demonstrate petrological and geochemical affinities between the magmas supplying modern eruptions and high-Mg, fall-stratified (FS) basalts ejected violently 4 k.y. ago. The FS primitive magmas (13 wt% MgO) are characteristically volatile enriched (at least 3.8 wt% H₂O and 3300 ppm CO₂), and bear a trace element signature of a garnet-bearing, metasomatized source (high Gd/Yb, K/La, U/Nb, Pb/Ce, Ca/Al). They started crystallizing olivine (Fo₉₁), clinopyroxene (Mg# 92.5), and Cr spinel deep in the plumbing system (>5 kbar), contributing to the cumulate piles at depth and to differentiated alkaline basalt and trachybasalt magmas in the shallow conduit. Continuous influx of mantle-derived, volatile-rich magmas, such as those that supplied the FS fallout, provides a good explanation for major compositional and eruptive features of Mount Etna.

Key Words: Mount Etna • volcano • picrite • melt inclusions • volatiles • degassing • mantle • meta-somatism

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