Impulsive Supply of Volatile-Rich Magmas in the Shallow Plumbing System of Mt. Etna Volcano

Cristina Perinelli,Danilo Palladino,Mario Gaeta,Piergiorgio Scarlato,Silvio Mollo,Serena De Cristofaro

doi:10.3390/min8110482

Cristina Perinelli, Danilo Palladino + Show 4 more

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https://doi.org/10.3390/min8110482

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Abstract

Magma dynamics at Mt. Etna volcano are frequently recognized as the result of complex crystallization regimes that, at shallow crustal levels, unexpectedly change from H2O-undersaturated to H2O-saturated conditions, due to the impulsive and irregular arrival of volatile-rich magmas from mantle depths. On this basis, we have performed hydrous crystallization experiments for a quantitative understanding of the role of H2O in the differentiation of deep-seated trachybasaltic magmas at the key pressure of the Moho transition zone. For H2O = 2.1–3.2 wt %, the original trachybasaltic composition shifts towards phonotephritic magmas never erupted during the entire volcanic activity of Mt. Etna. Conversely, for H2O = 3.8–8.2 wt %, the obtained trachybasalts and basaltic trachyandesites reproduce most of the pre-historic and historic eruptions. The comparison with previous low pressure experimental data and natural compositions from Mt. Etna provides explanation for (1) the abundant release of H2O throughout the plumbing system of the volcano during impulsive ascent of deep-seated magmas; (2) the upward acceleration of magmas feeding gas-dominated, sustained explosive eruptions; (3) the physicochemical changes of gas-fluxed magmas ponding at shallow crustal levels; and (4) the huge gas emissions measured at the summit craters and flank vents which result in a persistent volcanic gas plume.

Highlights

Considering the crystallization temperatures at the Moho depth recorded by clinopyroxene phenocrysts from lava fountains and lava flows, the results of our experiments show that the irregular arrival of deep-seated, volatile-rich magmas into the uppermost portions of the plumbing system may release a huge amount of H2 O with remarkable implications for the dynamics of H2 O-undersaturated magmas ponding at shallow crustal levels
Our experiments confirm that olivine is a late crystallizing phase from H2 O-undersaturated magmas equilibrated at high pressure
We found that the crystallization sequence, phase stability, textural and compositional evolution of natural minerals are directly correlated to the transition from H2 O-undersaturated to H2 O-saturated crystallization regimes

Summary

Introduction

The plumbing system of Mt. Etna volcano (Sicily, Italy) has a multifaceted geometry, variable in space and time and consisting of storage zones at different depths, where more or less primitive magmas containing variable H2 O contents undergo degassing, fractional crystallization and mixing processes (cf [1]). The explosive activity of the volcano is ascribed to the impulsive upward migration of gas-rich magmas and/or fluxes of abundant volatiles from the depths [2,3,4]. Evidence of pulsating volatile flushing is provided by the great volume of gases released from the summit craters and flanks of the volcano that clashes with the relatively small amount of erupted products [5]. The release of volatiles has drastic effects on the rheology of Etnean magmas and, the internal dynamics of the volcano [6]. The large quantities of gas released may change the geochemical and isotopic compositions of near-liquidus lavas erupted at the vents and flowing onto the surface [7]

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