Kinetics of iron oxidation-reduction in hydrous silicic melts
-
Fabrice Gaillard
,
Bruno Scaillet
Abstract
The kinetics of Fe oxidation-reduction in two hydrous rhyolitic melts, one metaluminous and the other peralkaline, have been studied at 800°C, 2kb, for melt water contents from ~5 wt% to saturation and fO2 between NNO-2 and NNO + 3 (NNO = nickel-nickel oxide redox buffer). The metaluminous melt (~1 wt% FeOT) reached redox equilibrium after 10 hours and the peralkaline one (~3 wt% FeOT) after 3 hours. The kinetics of Fe oxidation and reduction are similar and unaffected by the presence or absence of a hydrous fluid phase. No redox front is observable in the glass as the Fe3+/Fe2+ ratio evolves, implying that the Fe redox kinetics in hydrous silicic melts is rate-limited neither by the diffusion of H2 nor by the mobilities of divalent cations, as observed for anhydrous basaltic melts. We propose a two-step reaction mechanism that involves: (1) virtually instantaneous diffusion of H2 in the sample, followed by (2) slower structural/chemical reorganizations around Fe atoms. The overall redox process involving iron and hydrogen in Fe-poor, H2O-rich melts is thus reaction-limited and obeys a first-order logarithmic rate law. The relatively slow kinetics of oxidation/ reduction explains why melt Fe3+/Fe2+ can be readily quenched in laboratory experiments. Simulation of oxidation of magmas due to H2 exchange with wall rocks is performed using these new kinetics laws and two DH2 values extracted from the literature. We demonstrate that the metaluminous composition is not significantly modified whereas the peralkaline composition undergoes important and fast changes of Fe3+/Fe2+ during short processes such as ascent prior to Plinian-style eruptions
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Thermal equations of state for B1 and B2 KCl
- Determination of molar absorptivities for infrared absorption bands of H2O in andesitic glasses
- H2O activity in H2O-N2 fluids at high pressure and temperature measured by the brucitepericlase equilibrium
- Kinetics of iron oxidation-reduction in hydrous silicic melts
- Kinetics of cation ordering in synthetic MgAl2O4 spinel
- Structural properties and heat-induced oxidation-dehydrogenation of manganoan ilvaite from Perda Niedda mine, Sardinia, Italy
- Ultrahigh-pressure metamorphism in western Tianshan, China: Part I. Evidence from inclusions of coesite pseudomorphs in garnet and from quartz exsolution lamellae in omphacite in eclogites
- Ultra-high pressure metamorphism in western Tianshan, China: Part II. Evidence from magnesite in eclogite
- Discovery of clinoenstatite in garnet pyroxenites from the Dabie-Sulu ultrahigh-pressure terrane, east-central China
- Ultrahigh-pressure (UHP) low-Al titanites from carbonate-bearing rocks in Dabieshan- Sulu UHP terrane, eastern China
- Metamictization and recrystallization of titanite: An infrared spectroscopic study
- Fine structure of infrared OH-stretching bands in natural and heat-treated amphiboles of the tremolite-ferro-actinolite series
- Correlation between OH concentration and oxygen isotope diffusion rate in diopsides from the Adirondack Mountains, New York
- The substitution Fe3+-Al and the isosymmetric displacive phase transition in synthetic zoisite: A powder X-ray and infrared spectroscopy study
- In situ X-ray observation of the reaction dolomite = aragonite + magnesite at 900–1300 K
- High-pressure single-crystal X-ray and powder neutron study of F,OH/OD-chondrodite: Compressibility, structure, and hydrogen bonding
- Quantitative characterization of biotic iron oxides by analytical electron microscopy
- Synthesis and NMR characterization (1H and 31P MAS) of the fluorine-free hydroxylapatite–britholite-(Y) series
- Quantum mechanical calculations of dioctahedral 2:1 phyllosilicates: Effect of octahedral cation distributions in pyrophyllite, illite, and smectite
- The nature of disorder in montmorillonite by simulation of X-ray powder patterns
- Ferripedrizite, a new monoclinic BLi amphibole end-member from the Eastern Pedriza Massif, Sierra de Guadarrama, Spain, and a restatement of the nomenclature of Mg-Fe-Mn-Li amphiboles
- Description and crystal structure of vajdakite, [(Mo6+O2)2(H2O)2 As3+ 2O5]·H2O—A new mineral from Jáchymov, Czech Republic
- Some remarks on fission-track observational biases and crystallographic orientation effects
- Surface reconstruction and As-polymerization at fractured loellingite (FeAs2) surfaces
- The strength of moissanite
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Articles in the same Issue
- Thermal equations of state for B1 and B2 KCl
- Determination of molar absorptivities for infrared absorption bands of H2O in andesitic glasses
- H2O activity in H2O-N2 fluids at high pressure and temperature measured by the brucitepericlase equilibrium
- Kinetics of iron oxidation-reduction in hydrous silicic melts
- Kinetics of cation ordering in synthetic MgAl2O4 spinel
- Structural properties and heat-induced oxidation-dehydrogenation of manganoan ilvaite from Perda Niedda mine, Sardinia, Italy
- Ultrahigh-pressure metamorphism in western Tianshan, China: Part I. Evidence from inclusions of coesite pseudomorphs in garnet and from quartz exsolution lamellae in omphacite in eclogites
- Ultra-high pressure metamorphism in western Tianshan, China: Part II. Evidence from magnesite in eclogite
- Discovery of clinoenstatite in garnet pyroxenites from the Dabie-Sulu ultrahigh-pressure terrane, east-central China
- Ultrahigh-pressure (UHP) low-Al titanites from carbonate-bearing rocks in Dabieshan- Sulu UHP terrane, eastern China
- Metamictization and recrystallization of titanite: An infrared spectroscopic study
- Fine structure of infrared OH-stretching bands in natural and heat-treated amphiboles of the tremolite-ferro-actinolite series
- Correlation between OH concentration and oxygen isotope diffusion rate in diopsides from the Adirondack Mountains, New York
- The substitution Fe3+-Al and the isosymmetric displacive phase transition in synthetic zoisite: A powder X-ray and infrared spectroscopy study
- In situ X-ray observation of the reaction dolomite = aragonite + magnesite at 900–1300 K
- High-pressure single-crystal X-ray and powder neutron study of F,OH/OD-chondrodite: Compressibility, structure, and hydrogen bonding
- Quantitative characterization of biotic iron oxides by analytical electron microscopy
- Synthesis and NMR characterization (1H and 31P MAS) of the fluorine-free hydroxylapatite–britholite-(Y) series
- Quantum mechanical calculations of dioctahedral 2:1 phyllosilicates: Effect of octahedral cation distributions in pyrophyllite, illite, and smectite
- The nature of disorder in montmorillonite by simulation of X-ray powder patterns
- Ferripedrizite, a new monoclinic BLi amphibole end-member from the Eastern Pedriza Massif, Sierra de Guadarrama, Spain, and a restatement of the nomenclature of Mg-Fe-Mn-Li amphiboles
- Description and crystal structure of vajdakite, [(Mo6+O2)2(H2O)2 As3+ 2O5]·H2O—A new mineral from Jáchymov, Czech Republic
- Some remarks on fission-track observational biases and crystallographic orientation effects
- Surface reconstruction and As-polymerization at fractured loellingite (FeAs2) surfaces
- The strength of moissanite
- Diamond formation through carbonate-silicate interaction
- Anisotropic Fe-Mg diffusion in biotite
- Characterization of a high-pressure phase of silica from the Martian meteorite Shergotty
