Hydrogen and hydrogen sulphide in volcanic gases: abundance, processes, and atmospheric fluxes

Hydrogen (H2) and hydrogen sulphide (H2S) are typically present at only minor to trace levels in volcanic gas emissions, and yet they occupy a key role in volcanic degassing research in view of the control they exert on volcanic gas reducing capacity (e.g., their ability to remove atmospheric O2). In combination with other major compounds, H2 and H2S are also key to extracting information on source magma conditions (temperature and redox) from observed magmatic gas compositions. Here, we use a catalogue, compiled by extracting from the geological literature a selection of representative analyses of magmatic to mixed (magmatic–hydrothermal) gases, to review the processes that control H2 and H2S abundance in volcanic gases. We show that H2 concentrations and H2/H2O ratios in volcanic gases both exhibit strong positive temperature dependences, while H2S concentrations and H2S/SO2 ratios are temperature insensitive overall. The high H2 concentrations (and low H2S/SO2 compositions, of ∼0.1 on average) in high-temperature (>1000 °C) magmatic gases are overall consistent with those predicted thermodynamically assuming external redox buffering operated by the coexisting silicate melt, at oxygen fugacities ranging from ∆FMQ −1 to 0 (non-arc volcanoes) to ∆FMQ 0 to +2 (arc volcanoes) (where ∆FMQ is oxygen fugacity expresses as a log unit difference relative to the Fayalite–Magnetite–Quartz oxygen fugacity buffer). Lower temperature (<1000 °C) volcanic gases exhibit more oxidizing redox conditions (typically above the Nickel–Nickel Oxide buffer) that are caused by a combination of (i) gas re-equilibration during closed-system (gas-phase only) adiabatic cooling in a gas-buffered system, and (ii) heterogenous (gas–mineral) reactions. We show, in particular, that gas-phase equilibrium in the H2–H2S–H2O–SO2 system is overall maintained upon cooling down to ∼600 °C, while quenching of higher temperature equilibria (at which Apparent Equilibrium Temperatures, AETs, largely exceed measured discharge temperatures) is more frequently observed for higher extents of cooling (e.g., at T <600 °C). In such lower temperature volcanic environments, gas–mineral reactions also become increasingly important, scavenging magmatic SO2 and converting it into H2S and hydrothermal minerals (sulphates and sulphides). These heterogeneous reactions, when occurring, can also control the temperature dependence of the volcanic gas H2/H2O ratios. Finally, by using our volcanic gas dataset in tandem with recently published global volcanic SO2 and CO2 budgets, we provide refined estimates for total H2S (median, 1.4 Tg/yr; range, 0.9–8.8 Tg/yr) and H2 (median, 0.23 Tg/yr; range, 0.06–1 Tg/yr) fluxes from global subaerial volcanism

CP violation and final state interactions in B --> K pi pi decays

Effects of CP violation and of final state interactions between pairs of pseudoscalar mesons are studied in three-body B+, B-, B0 and antiB0 decays into K pi pi. An alternative approach to the isobar model for three-body B decays is proposed. It is based on the QCD factorization approximation and the knowledge of the meson-meson form factors. Some phenomenological charming penguin amplitudes are needed to describe the branching fractions, direct CP asymmetries of the quasi-two-body B --> K*(892) pi and B --> K0*(1430) pi decays as well as the K pi effective mass and the helicity angle distributions. The experimental branching fractions for the B --> K0*(1430) pi decay, obtained by the Belle and BaBar collaborations using the isobar model, are larger than our predictions by about 52 per cent.Comment: 3 pages, contribution to International Europhysics Conference on High Energy Physics HEP 2007, Manchester (England), July 19-25, 200

Fe-XANES analyses of Reykjanes Ridge basalts: Implications for oceanic crust's role in the solid Earth oxygen cycle

The cycling of material from Earth's surface environment into its interior can couple mantle oxidation state to the evolution of the oceans and atmosphere. A major uncertainty in this exchange is whether altered oceanic crust entering subduction zones can carry the oxidised signal it inherits during alteration at the ridge into the deep mantle for long-term storage. Recycled oceanic crust may be entrained into mantle upwellings and melt under ocean islands, creating the potential for basalt chemistry to constrain solid Earth–hydrosphere redox coupling. Numerous independent observations suggest that Iceland contains a significant recycled oceanic crustal component, making it an ideal locality to investigate links between redox proxies and geochemical indices of enrichment. We have interrogated the elemental, isotope and redox geochemistry of basalts from the Reykjanes Ridge, which forms a 700 km transect of the Iceland plume. Over this distance, geophysical and geochemical tracers of plume influence vary dramatically, with the basalts recording both long- and short-wavelength heterogeneity in the Iceland plume. We present new high-precision Fe-XANES measurements of Fe³⁺/∑Fe on a suite of 64 basalt glasses from the Reykjanes Ridge. These basalts exhibit positive correlations between Fe³⁺/∑Fe and trace element and isotopic signals of enrichment, and become progressively oxidised towards Iceland: fractionation-corrected Fe³⁺/∑Fe increases by ∼0.015 and ΔQFM by ∼0.2 log units. We rule out a role for sulfur degassing in creating this trend, and by considering various redox melting processes and metasomatic source enrichment mechanisms, conclude that an intrinsically oxidised component within the Icelandic mantle is required. Given the previous evidence for entrained oceanic crustal material within the Iceland plume, we consider this the most plausible carrier of the oxidised signal. To determine the ferric iron content of the recycled component ([Fe₂O₃]) we project observed liquid compositions to an estimate of Fe₂O₃ in the pure enriched endmember melt, and then apply simple fractional melting models, considering lherzolitic and pyroxenitic source mineralogies, to estimate [Fe₂O₃] content. Propagating uncertainty through these steps, we obtain a range of [Fe₂O₃] for the enriched melts (0.9–1.4 wt%) that is significantly greater than the ferric iron content of typical upper mantle lherzolites. This range of ferric iron contents is consistent with a hybridised lherzolite–basalt (pyroxenite) mantle component. The oxidised signal in enriched Icelandic basalts is therefore potential evidence for seafloor–hydrosphere interaction having oxidised ancient mid-ocean ridge crust, generating a return flux of oxygen into the deep mantle.OS was supported by a Title A Fellowship from Trinity College, JM through NERC grant NE/J021539/1 and MH acknowledges a Junior Research Fellowship from Murray Edwards College, Cambridge. We acknowledge Diamond Light Source for time on beamline I18 under proposals SP9446, SP9456 and SP12130 and the support during our analytical sessions from beamline scientist Konstantin Ignatyev and principal beamline scientist Fred Mosselmans. The Smithsonian Institution National Museum of Natural History is thanked for their loan of NMNH 117393.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.epsl.2015.07.01

QCD Short-distance Constraints and Hadronic Approximations

This paper discusses a general class of ladder resummation inspired hadronic approximations. It is found that this approach naturally reproduces many successes of single meson per channel saturation models (e.g. VMD) and NJL based models. In particular the existence of a constituent quark mass and a gap equation follows naturally. We construct an approximation that satisfies a large set of QCD short-distance and large $N_c$ constraints and reproduces many hadronic observables. We show how there exists in general a problem between QCD short-distance constraints for Green Functions and those for form factors and cross-sections following from the quark-counting rule. This problem while expected for Green functions that do not vanish in purely perturbative QCD also persists for many Green functions that are order parameters.Comment: 27 page

The impact of degassing on the oxidation state of basaltic magmas: A case study of Kīlauea volcano

Volcanic emissions link the oxidation state of the Earth's mantle to the composition of the atmosphere. Whether the oxidation state of an ascending magma follows a redox buffer – hence preserving mantle conditions – or deviates as a consequence of degassing remains under debate. Thus, further progress is required before erupted basalts can be used to infer the redox state of the upper mantle or the composition of their co-emitted gases to the atmosphere. Here we present the results of X-ray absorption near-edge structure (XANES) spectroscopy at the iron K-edge carried out for a series of melt inclusions and matrix glasses from ejecta associated with three eruptions of Kīlauea volcano (Hawai‘i). We show that the oxidation state of these melts is strongly correlated with their volatile content, particularly in respect of water and sulfur contents. We argue that sulfur degassing has played a major role in the observed reduction of iron in the melt, while the degassing of H$_{2}$O and CO$_{2}$ appears to have had a negligible effect on the melt oxidation state under the conditions investigated. Using gas–melt equilibrium degassing models, we relate the oxidation state of the melt to the composition of the gases emitted at Kīlauea. Our measurements and modelling yield a lower constraint on the oxygen fugacity of the mantle source beneath Kīlauea volcano, which we infer to be near the nickel nickel-oxide (NNO) buffer. Our findings should be widely applicable to other basaltic systems and we predict that the oxidation state of the mantle underneath most hotspot volcanoes is more oxidised than that of the associated lavas. We also suggest that whether the oxidation states of a basalt (in particular MORB) reflects that of its source, is primarily determined by the extent of sulfur degassing.We thank the Diamond Light Source for access to beamline I18 (proposal number SP11497-1) that contributed to the results presented here and the invaluable support during our analytical sessions from Konstantin Ignatyev. The Smithsonian Institution National Museum of Natural History is thanked for their loan of NMNH 117393. We thank Don Swanson (HVO-USGS) for his help acquiring the samples. YM acknowledges support from the Scripps Institution of Oceanography Postdoctoral Fellowship program. We are grateful to Nicole Métrich and an anonymous reviewer for providing valuable comments improving the quality of the manuscript. ME and CO are supported by the Natural Environment Research Council via the Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET). NP is also funded by the Natural Environment Research Council (grant NE/N009312/1). NERC-funded studentship funded sample collection. ME acknowledges NERC ion probe grant IMF376/0509.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.epsl.2016.06.031

Volcanic gas emissions and degassing dynamics at Ubinas and Sabancaya volcanoes; implications for the volatile budget of the central volcanic zone

Emission of volcanic gas is thought to be the dominant process by which volatiles transit from the deep earth to the atmosphere. Volcanic gas emissions, remain poorly constrained, and volcanoes of Peru are entirely absent from the current global dataset. In Peru, Sabancaya and Ubinas volcanoes are by far the largest sources of volcanic gas. Here, we report the first measurements of the compositions and fluxes of volcanic gases emitted from these volcanoes. The measurements were acquired in November 2015. We determined an average SO2 flux of 15.3 ± 2.3 kg s− 1 (1325-ton day− 1) at Sabancaya and of 11.4 ± 3.9 kg s− 1 (988-ton day− 1) at Ubinas using scanning ultraviolet spectroscopy and dual UV camera systems. In-situ Multi-GAS analyses yield molar proportions of H2O, CO2, SO2, H2S and H2 gases of 73, 15, 10 1.15 and 0.15 mol% at Sabancaya and of 96, 2.2, 1.2 and 0.05 mol% for H2O, CO2, SO2 and H2S at Ubinas. Together, these data imply cumulative fluxes for both volcanoes of 282, 30, 27, 1.2 and 0.01 kg s− 1 of H2O, CO2, SO2, H2S and H2 respectively. Sabancaya and Ubinas volcanoes together contribute about 60% of the total CO2 emissions from the Central Volcanic zone, and dominate by far the total revised volatile budget of the entire Central Volcanic Zone of the Andes

First In-Situ Measurements of Plume Chemistry at Mount Garet Volcano, Island of Gaua (Vanuatu)

Recent volcanic gas compilations have urged the need to expand in-situ plume measurements to poorly studied, remote volcanic regions. Despite being recognized as one of the main volcanic epicenters on the planet, the Vanuatu arc remains poorly characterized for its subaerial emissions and their chemical imprints. Here, we report on the first plume chemistry data for Mount Garet, on the island of Gaua, one of the few persistent volatile emitters along the Vanuatu arc. Data were collected with a multi-component gas analyzer system (multi-GAS) during a field campaign in December 2018. The average volcanic gas chemistry is characterized by mean molar CO2/SO2, H2O/SO2, H2S/SO2 and H2/SO2 ratios of 0.87, 47.2, 0.13 and 0.01, respectively. Molar proportions in the gas plume are estimated at 95.9 ± 11.6, 1.8 ± 0.5, 2.0 ± 0.01, 0.26 ± 0.02 and 0.06 ± 0.01, for H2O, CO2, SO2, H2S and H2. Using the satellite-based 10-year (2005–2015) averaged SO2 flux of ~434 t d−1 for Mt. Garet, we estimate a total volatile output of about 6482 t d−1 (CO2 ~259 t d−1; H2O ~5758 t d−1; H2S ~30 t d−1; H2 ~0.5 t d−1). This may be representative of a quiescent, yet persistent degassing period at Mt. Garet; whilst, as indicated by SO2 flux reports for the 2009–2010 unrest, emissions can be much higher during eruptive episodes. Our estimated emission rates and gas composition for Mount Garet provide insightful information on volcanic gas signatures in the northernmost part of the Vanuatu Arc Segment. The apparent CO2-poor signature of high-temperature plume degassing at Mount Garet raises questions on the nature of sediments being subducted in this region of the arc and the possible role of the slab as the source of subaerial CO2. In order to better address the dynamics of along-arc volatile recycling, more volcanic gas surveys are needed focusing on northern Vanuatu volcanoes

First in-situ measurements of plume chemistry at mount garet volcano, island of gaua (Vanuatu)

Recent volcanic gas compilations have urged the need to expand in-situ plume measurements to poorly studied, remote volcanic regions. Despite being recognized as one of the main volcanic epicenters on the planet, the Vanuatu arc remains poorly characterized for its subaerial emissions and their chemical imprints. Here, we report on the first plume chemistry data for Mount Garet, on the island of Gaua, one of the few persistent volatile emitters along the Vanuatu arc. Data were collected with a multi-component gas analyzer system (multi-GAS) during a field campaign in December 2018. The average volcanic gas chemistry is characterized by mean molar CO2 /SO2, H2 O/SO2, H2 S/SO2 and H2 /SO2 ratios of 0.87, 47.2, 0.13 and 0.01, respectively. Molar proportions in the gas plume are estimated at 95.9 ± 11.6, 1.8 ± 0.5, 2.0 ± 0.01, 0.26 ± 0.02 and 0.06 ± 0.01, for H2 O, CO2, SO2, H2 S and H2 . Using the satellite-based 10-year (2005–2015) averaged SO2 flux of ~434 t d−1 for Mt. Garet, we estimate a total volatile output of about 6482 t d−1 (CO2 ~259 t d−1; H2 O ~5758 t d−1; H2 S ~30 t d−1; H2 ~0.5 t d−1 ). This may be representative of a quiescent, yet persistent degassing period at Mt. Garet; whilst, as indicated by SO2 flux reports for the 2009–2010 unrest, emissions can be much higher during eruptive episodes. Our estimated emission rates and gas composition for Mount Garet provide insightful information on volcanic gas signatures in the northernmost part of the Vanuatu Arc Segment. The apparent CO2-poor signature of high-temperature plume degassing at Mount Garet raises questions on the nature of sediments being subducted in this region of the arc and the possible role of the slab as the source of subaerial CO2 . In order to better address the dynamics of along-arc volatile recycling, more volcanic gas surveys are needed focusing on northern Vanuatu volcanoes

Megacrystals track magma convection between reservoir and surface

Active volcanoes are typically fed by magmatic reservoirs situated within the upper crust. The development of thermal and/or compositional gradients in such magma chambers may lead to vigorous convection as inferred from theoretical models and evidence for magma mixing recorded in volcanic rocks. Bi-directional flow is also inferred to prevail in the conduits of numerous persistently-active volcanoes based on observed gas and thermal emissions at the surface, as well as experiments with analogue models. However, more direct evidence for such exchange flows has hitherto been lacking. Here, we analyse the remarkable oscillatory zoning of anorthoclase feldspar megacrystals erupted from the lava lake of Erebus volcano, Antarctica. A comprehensive approach, combining phase equilibria, solubility experiments and melt inclusion and textural analyses shows that the chemical profiles are best explained as a result of multiple episodes of magma transport between a deeper reservoir and the lava lake at the surface. Individual crystals have repeatedly travelled up-and-down the plumbing system, over distances of up to several kilometers, presumably as a consequence of entrainment in the bulk magma flow. Our findings thus corroborate the model of bi-directional flow in magmatic conduits. They also imply contrasting flow regimes in reservoir and conduit, with vigorous convection in the former (regular convective cycles of ∼150 days at a speed of ∼0.5 mm s−1) and more complex cycles of exchange flow and re-entrainment in the latter. We estimate that typical, 1-cm-wide crystals should be at least 14 years old, and can record several (from 1 to 3) complete cycles between the reservoir and the lava lake via the conduit. This persistent recycling of phonolitic magma is likely sustained by CO2 fluxing, suggesting that accumulation of mafic magma in the lower crust is volumetrically more significant than that of evolved magma within the edifice.The work reported here has been partially supported by the National Science Foundation (Division of Polar Programs) under grant ANT1142083. The authors thank the Natural Environment Research Council (NERC) for access to the NERC Ion Microprobe Facility (Grant IMF453/1011) and Richard Hinton for invaluable help with SIMS analyses. Y.M. acknowledges support from the Cambridge Philosophical Society, the University of Cambridge Home and EU Scholarship Scheme, and the Philip Lake and William Vaughan Lewis funds from the Department of Geography, University of Cambridge. Y.M. also acknowledges support from ERC grant #279790.This is the final published version. It first appeared at http://www.sciencedirect.com/science/article/pii/S0012821X14007833#

Hot Nucleons in Chiral Soliton Models

Chiral lagrangians as effective field theories of QCD are most suitable for the study of nucleons in a hot pion gas because they contain pions and also baryons as solitons of the same action. The semiclassical treatment of the soliton solutions must be augmented by pionic fluctuations which requires renormalisation to 1-loop, and finite temperatures do not introduce new ultraviolet divergencies and may easily be considered. Alternatively, a renormalisation scheme based on the renormalisation group equation at finite temperature comprises and extends the rigorous results of chiral perturbation theory and renders the low energy constants temperature-dependent which allows the construction of temperature-dependent solitons below the critical temperature. The temperature-dependence of the baryon energy and the pion-nucleon coupling is studied. There is no simple scaling law for the temperature-dependence of these quantities.Comment: 17 pages (RevTeX), 5 figure