Timescales of water accumulation in magmas and implications for short warning times of explosive eruptions

M Petrelli,Y Le Guer,D Perugini,G La Spina,L Spina,K El Omari

doi:10.1038/s41467-018-02987-6

M Petrelli, Y Le Guer + Show 4 more

Open Access

https://doi.org/10.1038/s41467-018-02987-6

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Abstract

Water plays a key role in magma genesis, differentiation, ascent and, finally, eruption. Despite the recognized crucial function of water, there are still several issues that continue to blur our view about its role in magmatic systems. What are the timescales of H2O accumulation in crystallizing magmas? What are the ascent rates of water-rich residual melts leading to explosive eruptions? Here, we track the timescale of water accumulation in a residual melt resulting from crystallization of a hydrous CO2-bearing magmatic mass stored at mid- to deep-crustal levels in a subduction-related geodynamic setting. Our results indicate that, after a repose period ranging from few to several thousand years, water-rich melts with water concentrations larger than 6–9 wt.% can migrate towards the Earth surface in very short timescales, on the order of days or even hours, possibly triggering explosive eruptions with short warning times and devoid of long-term geophysical precursors.

Highlights

Water plays a key role in magma genesis, differentiation, ascent and, eruption
We focus on pressures between 0.7 and 1.0 GPa, corresponding to crustal depths ranging between ~20 and 35 km
In a magmatic system subjected to isobaric cooling, melt solubilities for water and carbon dioxide will progressively evolve in response to thermal and chemical changes

Summary

Introduction

Water plays a key role in magma genesis, differentiation, ascent and, eruption. We track the timescale of water accumulation in a residual melt resulting from crystallization of a hydrous CO2-bearing magmatic mass stored at mid- to deep-crustal levels in a subduction-related geodynamic setting. Melt inclusions may not correctly archive information about the H2O–CO2 systematics at deeper levels, hindering de facto a reliable estimation of water and carbon dioxide contents in magmas evolving at middle and lower crustal depths. The presence of water-rich magmas (H2O ≥ 8.0 wt.%) at mid-crustal levels is supported by recent studies combining geophysical investigations, laboratory experiments, and petrological data to constrain deep electrical conductivity anomalies beneath the Uturuncu Volcano (Central Andes)[26]. What are the ascent velocities of volatile-rich residual melts (produced by the crystallization of volatile-bearing parental magmas at mid- to deep-crustal levels) toward the Earth surface, eventually culminating in explosive volcanic eruptions? Key questions include: What are the timescales for volatiles accumulation in crystallizing magmas at mid- to deep-crustal levels? What are the ascent velocities of volatile-rich residual melts (produced by the crystallization of volatile-bearing parental magmas at mid- to deep-crustal levels) toward the Earth surface, eventually culminating in explosive volcanic eruptions?

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