The role of melt composition on aqueous fluid vs. silicate melt partitioning of bromine in magmas
Introduction
Volcanic degassing is an important process in sustaining the composition of Earth's atmosphere (e.g., Gaillard and Scaillet, 2014, Mather, 2015). Whilst much progress has been made constraining global volcanic fluxes, uncertainties remain regarding the emissions of the key halogen species, especially the trace Br- and I-bearing species (Pyle and Mather, 2009). However, improvements in remote sensing techniques and analytical techniques, and their application to an increasing number of active volcanoes, have provided new data on the concentrations of these minor components in volcanic gases (e.g., Gerlach, 2004, Aiuppa et al., 2005, Aiuppa, 2009, Bobrowski et al., 2015), which in turn can be used to better constrain their global fluxes to the atmosphere (Pyle and Mather, 2009). Bromine has received particular attention over the last decade, owing to its important role in atmospheric chemistry in general (e.g., Oppenheimer et al., 2006; Roberts et al., 2009, Roberts et al., 2014) and ozone depletion in the troposphere and stratosphere in particular (von Glasow et al., 2009, Kutterolf et al., 2013, Cadoux et al., 2015). Global compilations show that Br sources (emissions to the atmosphere) and sinks (removal routes from the atmosphere) are not strictly balanced, hinting at a missing natural source of Br (Montzka et al., 2011). The direct detection of HBr and BrO in volcanic plumes (Bobrowski et al., 2003, Aiuppa et al., 2005) suggests that volcanic activity may be one such a source.
The correct evaluation of the contribution of past volcanic eruptions to atmospheric chemistry depends on our ability to evaluate Br behaviour in magmas, in particular its partitioning between silicate melt and gas phases. So far, only a few experimental studies have been performed on this topic, and have investigated Br behaviour in synthetic albite to rhyolite melt compositions (Bureau et al., 2000, Bureau and Métrich, 2003). However, natural silicate melt compositions can depart significantly from such model systems, in particular by having elevated contents of Fe, Mg or Ca, which (as Na) can complex with halogens thereby enhancing their solubility in silicate melts (Cochain et al., 2015). The relationship between halogen solubility and their complexation with cations has been shown for Cl; chlorine solubility in most silicate melts is dominantly controlled by the abundances of , but Ti, F, and P also have strong influences (e.g., Webster et al., 1999; Webster and De Vivo, 2002). There is thus a need to evaluate the role of melt composition on Br behaviour in magmas, which is the main motivation of the present study. To that end, we have performed fluid/melt partitioning experiments on natural basalt, andesite and rhyodacite compositions under P–T–H2O–redox storage conditions relevant to shallow arc magmas. Combining our Br partition coefficient for the basaltic composition, with other experimental data on S and Cl behaviour, and volcanic gas compositions from the literature, we develop a simple first-order model to predict the S–Cl–Br degassing behaviour in mafic systems. We also measure Br contents of melt inclusions from Etna, Stromboli, Merapi and Santorini eruptions and estimate the mass of bromine in the pre-eruptive magmas, this allows us to address the atmospheric contribution of open-vent mafic volcanoes versus that of intermediate-silicic volcanoes.
Section snippets
Starting material
The selected starting materials are natural volcanic rocks: a hawaiitic basalt from a 2002 Etna eruption (Lesne et al., 2011a, Lesne et al., 2011b; Iacono-Marziano et al., 2012), a calc-alkaline andesite and a rhyodacite from the Santorini Upper Scoria-2 (USC-2) and Minoan eruptions, respectively (Cadoux et al., 2017). The whole rocks were crushed and ground in an agate mortar. About 10 g of the powders were melted twice (and ground in between), to ensure homogenization, in a platinum crucible
Major element analysis
Experimental glasses and natural melt inclusions were analyzed for their major elements by electron microprobe (EMP) using the joint ISTO-BRGM SX-Five microbeam facility (Orléans, France). The operating conditions were: 15 kV accelerating voltage, 4–6 nA beam current, 10 s counting time on peaks, 5 s on background. The standards used were: albite for Si and Na, TiMnO3 for Ti and Mn, Al2O3 for Al, Fe2O3 for Fe, MgO for Mg, andradite for Ca and orthose for K. Alkalis were analyzed first and a
Major element compositions
Average major element compositions of experimental glasses and melt inclusions are presented in Tables 3 and A.2, respectively. Comparison of the experimental products (Table 3) with the corresponding starting dry glasses (Table 1) shows a systematic gain in Na2O due to the addition of sodium through the H2O–NaBr solution in the experimental charges (10 to 153 μg of Na were incorporated into the final glass, Table A.1), and a loss in FeO (up to 14% taking into account standard deviations) in
Halogen behaviour
This section aims to place our novel Br partitioning data in the wider framework of halogen behaviour. Hereafter, we provide a brief, non-exhaustive review of chlorine, fluorine and iodine partitioning and make comparisons with bromine.
Many studies have been dedicated to understanding the partitioning behaviour of halogens between fluids and silicate melts (e.g., Webster, 1990, Webster and Holloway, 1990; Webster, 1992a, Webster, 1992b; Webster et al., 1999, Signorelli and Carroll, 2000, Bureau
Conclusions
Determining halogen behaviour in magmatic systems is important to understand their role in the Earth's element cycles and to provide reliable constraints on the contribution of volcanism to atmospheric and ocean chemistry. The behaviour of the heavier halogens such as Br in magmatic systems is less well understood than that of Cl and F. We have experimentally determined the fluid/melt partitioning of bromine at shallow crustal pressure and temperature conditions (100–200 MPa, 900–1200 °C) with
Acknowledgments
A.C. thanks N. Bouden (CRPG, Nancy) for his assistance during H2O SIMS measurements, and S. Erdmann (ISTO, Orléans) who provided crystal mounts from Merapi andesite for melt inclusions analysis. A.C. is also grateful to Y. Missenard and P. Sarda (GEOPS, Orsay) for their help and discussion about error propagation. N. Metrich (IPGP, Paris) and A. Bertagnini (INGV, Pisa) provided melt inclusions from Stromboli. I. Di Carlo (ISTO, Orléans) and L. Brusca (INGV, Palermo) are acknowledged for their
References (113)
Degassing of halogens from basaltic volcanism: insights from volcanic gas observations
Chem. Geol.
(2009)- et al.
Halogens in volcanic systems
Chem. Geol.
(2009) - et al.
Halogen diffusion in a basaltic melt
Geochim. Cosmochim. Acta
(2007) - et al.
Chlorine partitioning between a basaltic melt and H2O–CO2 fluids at Mount Etna
Chem. Geol.
(2009) - et al.
Chloride partitioning and solubility in hydrous phonolites from Erebus volcano: a contribution towards a multi-component degassing model
Geo. Res. J.
(2014) - et al.
Fluid saturation and volatile partitioning between melts and hydrous fluids in crustal magmatic systems: the contribution of experimental measurements and solubility models
Earth-Sci. Rev.
(2012) - et al.
Partitioning of sulfur and chlorine between aqueous fluid and basaltic melt at 1050 °C, 100 and 200 MPa
Chem. Geol.
(2015) - et al.
Sulfur and chlorine solubility in Mt. Unzen rhyodacitic melt at 850 °C and 200 MPa
Chem. Geol.
(2004) - et al.
An experimental study of bromine behaviour in water-saturated silicic melts
Geochim. Cosmochim. Acta
(2003) - et al.
Volcanic degassing of bromine and iodine: experimental fluid/melt partitioning data and applications to stratospheric chemistry
Earth Planet. Sci. Lett.
(2000)
Bromine cycle in subduction zones through in situ Br monitoring in diamond anvil cells
Geochim. Cosmochim. Acta
Modern and past volcanic degassing of iodine
Geochim. Cosmochim. Acta
A new set of standards for in-situ measurement of bromine abundances in natural silicate glasses: application to SR-XRF, LA-ICP-MS and SIMS techniques
Chem. Geol.
Bromine speciation in hydrous silicate melts at high pressure
Chem. Geol.
Halogen degassing during ascent and eruption of water-poor basaltic magma
Chem. Geol.
Kinetic vs. thermodynamic control of degassing of H2O–S±Cl-bearing andesitic melts
Geochim. Cosmochim. Acta
Trace element partitioning between vapor, brine and halite under extreme phase separation conditions
Geochim. Cosmochim. Acta
A theoretical framework for volcanic degassing chemistry in a comparative planetology perspective and implications for planetary atmospheres
Earth Planet. Sci. Lett.
New experimental data and semi-empirical parameterization of H2O–CO2 solubility in mafic melts
Geochim. Cosmochim. Acta
Sulfur K-edge XANES analysis of natural and synthetic basaltic glasses: implications for S-speciation and S content as function of oxygen fugacity
Geochim. Cosmochim. Acta
Subduction-related halogens (Cl, Br and I) and H2O in magmatic glasses from Southwest Pacific Backarc Basins
Earth Planet. Sci. Lett.
The implications of H2S and H2 stability in high-T mixtures of magmatic and atmospheric gases for the production of oxidized trace species (e.g., BrO and NOx)
Chem. Geol.
Volcanoes and the environment: lessons for understanding Earth's past and future from studies of present-day volcanic emissions
J. Volcanol. Geotherm. Res.
Halogens and trace metal emissions from the ongoing 2008 summit eruption of Kīlauea volcano, Hawaìi
Geochim. Cosmochim. Acta
Water content, δD and B tracking in the Vanuatu arc magmas (Aoba Island): insights from olivine-hosted melt inclusions
Lithos
2001 flank eruption of the alkali- and volatile-rich primitive basalt responsible for Mount Etna's evolution in the last three decades
Earth Planet. Sci. Lett.
Solubility and speciation of sulfur in silicate melts: the Conjugated Toop–Samis–Flood–Grjotheim (CTSFG) model
Geochim. Cosmochim. Acta
Source strength assessment of volcanic trace elements emitted from the Indonesian Arc
J. Volcanol. Geotherm. Res.
BrO formation in volcanic plumes
Geochim. Cosmochim. Acta
Halogens in igneous processes and their fluxes to the atmosphere and oceans from volcanic activity: a review
Chem. Geol.
Modelling reactive halogen formation and ozone depletion in volcanic plumes
Chem. Geol.
Gas and aerosol emissions from Villarrica volcano, Chile
J. Volcanol. Geotherm. Res.
Fractionation of Cl/Br during fluid phase separation in magmatic–hydrothermal fluids
Geochim. Cosmochim. Acta
Solubility of H2O- and CO2-bearing fluids in tholeiitic basalts at pressures up to 500 MPa
Chem. Geol.
Solubility and fluid–melt partitioning of Cl in hydrous phonolitic melts
Geochim. Cosmochim. Acta
A multiplatform code for the analysis of energy-dispersive X-ray fluorescence spectra
Spectrochim. Acta Part B
S–Cl–F degassing pattern of water rich alkali basalt: modelling and relationship with eruption styles of Mount Etna volcano
Earth Planet. Sci. Lett.
Solubility of H2O- and chlorine-bearing fluids in basaltic melt of Mount Etna at and MPa
Chem. Geol.
The 2010 explosive eruption of Java's Merapi volcano – a ‘100-year’ event
J. Volcanol. Geotherm. Res.
The effects of volcanic eruptions on atmospheric chemistry
Chem. Geol.
Water solubility and chlorine partitioning in Cl-rich granitic systems: effects of melt composition at 2 kbar and 800 °C
Geochim. Cosmochim. Acta
S, Cl and F degassing as an indicator of volcanic dynamics: the 2001 eruption of Mount Etna
Geophys. Res. Lett.
Emission of bromine and iodine from Mount Etna volcano
Geochem. Geophys. Geosyst.
Forecasting Etna eruptions by real-time observation of volcanic gas composition
Geology
Total volatile flux from Mount Etna
Geophys. Res. Lett.
First volatile inventory for Gorely volcano, Kamchatka
Geophys. Res. Lett.
First measurements of magmatic gas composition and fluxes during an eruption (October 2010) of Piton de la Fournaise hot spot volcano, La Reunion Island
Experimental Investigation of Halogen Diffusivity and Solubility in Etnean Basaltic Melts
Modeling the solubility of sulfur in magmas: a 50-year old geochemical challenge
The Solubility of Sulfur and Chlorine in H2O-Bearing Dacites of Krakatau and Basalts of Mt. Etna
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