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

Abstract

The volcanic hazard potential of Mount Etna volcano is currently nourished by longlasting , 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 modifi cations 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 affi nities between the magmas supplying modern eruptions and high-Mg, fallstratifi ed (FS) basalts ejected violently ~4 k.y. ago. The FS primitive magmas (~13 wt% MgO) are characteristically volatile enriched (at least 3.8 wt% H 2 O and 3300 ppm CO 2 ), 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 (Fo 91 ), 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 infl ux 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.

A two-component mantle source feeding Mt. Etna magmatism: Insights from the geochemistry of primitive magmas

“…4. Tephra FS sample, which is from highly vesiculated (voids = 60 vol.%) scoria lapilli from the sub-Plinian FS eruption (3930 ± 60 y BP; Coltelli et al, 2005) fed by volatile-rich picritic magma that rapidly ascended from the source zone (Kamenetsky et al, 2007 Trace elements were analyzed by an Agilent 7500 ICP mass spectrometer at Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Palermo. Selected portions of samples were crushed and powdered with an agate mortar, then a weighed aliquot (~100 mg) was digested using HF and HNO 3 .…”

Bubbles matter: An assessment of the contribution of vapor bubbles to melt inclusion volatile budgets

“…The occurrence of carbonates (and other minerals) on the bubble wall has been observed in MI from various volcanic settings (Kamenetsky and Kamenetsky, 2010 and references therein). However, such phases are usually not reported in studies that focus on volcanic degassing behavior (e.g., Kamenetsky et al, 2007). The presence of carbonate minerals on the bubble wall implies that analysis of the glass phase and vapor bubbles in MI may not completely account for all of the C that was originally trapped in a MI as dissolved CO 2 .…”

“…Some workers have avoided or limited the use of MI that contain bubbles (Lowenstern, 1994;Wallace and Gerlach, 1994;Wallace et al, 1999;Helo et al, 2011;Esposito et al, 2011;Lloyd et al, 2013). When only bubble-bearing MI were available for study, some workers have acknowledged potential contributions from the bubble by stating that the CO 2 contents and pressures determined from the MI are minimum values (Anderson and Brown, 1993;Cervantes and Wallace, 2003;Spilliaert et al, 2006;Kamenetsky et al, 2007;Johnson et al, 2008;Vigouroux et al, 2008;Ruscitto et al, 2010;Esposito et al, 2011). Others report that bubbles are present, but do not further discuss their potential contribution to MI volatile abundances (Lowenstern, 1994;Roggensack et al, 1997;Walker, 2003;Liu et al, 2006;Mangiacapra et al, 2008;Lloyd et al, 2013).…”

Quantification of the CO 2 budget and H 2 O–CO 2 systematics in subduction-zone magmas through the experimental hydration of melt inclusions in olivine at high H 2 O pressure

“…At such margins large amounts of CO 2 in sediments and oceanic (GEOROC, 2014). Before this study, the highest CO 2 content was measured in MIs from Etna (Kamenetsky et al, 2007) and Colima (Vigouroux et al, 2008) volcanoes. (b) Olivine-hosted melt inclusions from volcanic rocks from Klyuchevskoy Volcano rocks: natural glassy inclusions (Auer et al, 2009;Mironov and Portnyagin, 2011;this study); reheated at 0.1 MPa and 300 MPa without H 2 O (Mironov and Portnyagin, 2011;this study); and rehydrated at high H 2 O pressure (300-500 MPa, this study).…”