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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. B10, 2463, doi:10.1029/2002JB002095, 2003

Evidence of deep magma degassing and ascent by geochemistry of peripheral gas emissions at Mount Etna (Italy): Assessment of the magmatic reservoir pressure

Antonio Caracausi

Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy


Francesco Italiano

Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy


Antonio Paonita

Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy


Andrea Rizzo

Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy


P. Mario Nuccio

Dipartimento di Chimica e Fisica della Terra ed Applicazioni, University of Palermo, Palermo, Italy


Abstract

Five gas discharges in the area of Mount Etna volcano (Italy) and in the near Hyblean plateau have been monitored since 1996. All the emissions displayed low contributions from crustal fluids, whereas magmatic gases were the main component. Selective dissolution of these gases into hydrothermal aquifers has been recognized and modeled, allowing us to calculate the original composition of the magma-released gases. The inferred composition of the magmatic gases exhibits synchronous variations of He/Ne and He/CO2 ratios, which are coherent with the magma degassing process. On the basis of numerical simulations of volatile degassing from Etnean basalts we have computed the initial and final pressures of the magma batches feeding the emissions. We thus can define the levels of the Etna plumbing system where magmas are stored. Pressure values were around 360 and 160 MPa for initial and final stages, respectively, meaning related depths of about 10 and 3 km below sea level, matching those obtained by geophysical investigations for the deep and shallow magma reservoirs. In addition, we have been able to recognize episodes of magma migration from the deeper reservoir toward the shallow one. An important magma injection into the shallow storage volume was detected during the onset of the 2001 eruption (17 July). No further injection had taken place during this period until September 2001, providing a possible reason for the quick exhaustion of the eruption. In view of this we suggest that the sampled emissions are a powerful geochemical tool to investigate the Etna's plumbing system and its magma dynamics, as well as the development of eruptive events.

Received 12 July 2002; accepted 29 April 2003; published 9 October 2003.

Index Terms: 1010 Geochemistry: Chemical evolution; 8145 Tectonophysics: Physics of magma and magma bodies; 8419 Volcanology: Eruption monitoring (7280).

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Citation: Caracausi, A., F. Italiano, A. Paonita, A. Rizzo, and P. M. Nuccio (2003), Evidence of deep magma degassing and ascent by geochemistry of peripheral gas emissions at Mount Etna (Italy): Assessment of the magmatic reservoir pressure, J. Geophys. Res., 108(B10), 2463, doi:10.1029/2002JB002095.