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The influence of magmatic differentiation on the oxidation state of Fe in a basaltic arc magma
- Earth and Planetary Science Letters
, 2012
"... Subduction zone basalts are more oxidized than basalts from other tectonic settings (e.g., higher Fe 3 + /∑Fe), and this contrast may play a central role in the unique geochemical processes that generate arc and continental crust. The processes generating oxidized arc magmas, however, are poorly co ..."
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Subduction zone basalts are more oxidized than basalts from other tectonic settings (e.g., higher Fe 3 + /∑Fe), and this contrast may play a central role in the unique geochemical processes that generate arc and continental crust. The processes generating oxidized arc magmas, however, are poorly constrained, although they appear inherently linked to subduction. Near-surface differentiation processes unique to arc settings might drive oxidation of magmas that originate in equilibrium with a relatively reduced mantle source. Alternatively, arc magmas could record the oxidation conditions of a relatively oxidized mantle source. Here, we present new measurements of olivine-hosted melt inclusions from a single eruption of Agrigan volcano, Marianas, in order to test the influence of differentiation processes vs. source conditions on the Fe 3 + /∑Fe ratio, a proxy for system oxygen fugacity (fO 2 ). We determined Fe 3 + /∑Fe ratios in glass inclusions using μ-XANES and couple these data with major elements, dissolved volatiles, and trace elements. After correcting for post-entrapment crystallization, Fe 3+ /∑Fe ratios in the Agrigan melt inclusions (0.219 to 0.282), and their modeled fO 2 s (ΔQFM +1.0 to +1.8), are uniformly more oxidized than MORB, and preserve a portion of the evolution of this magma from 5.7 to 3.2 wt.% MgO. Fractionation of olivine ±clinopyroxene ±plagioclase should increase Fe 3+ /∑Fe as MgO decreases in the melt, but the data show Fe 3+ /∑Fe ratios decreasing as MgO decreases below 5 wt.% MgO. The major element trajectories, taken in combination with this strong reduction trend, are inconsistent with crystallization of common ferromagnesian phases found in the bulk Agrigan sample, including magnetite. Rather, decreasing Fe 3+ /∑Fe ratios correlate with decreasing S concentrations, suggesting that electronic exchanges associated with SO 2 degassing may dominate Fe 3+ /∑Fe variations in the melt during differentiation. In the case of this magma, the dominant effect of differentiation on magmatic fO 2 is reduction rather than oxidation. Tracing back Agrigan melts with MgO>5 wt.% (i.e., minimally degassed for S) along a modeled olivine fractionation trend to primary melts in equilibrium with Fo 90 olivine reveals melts in equilibrium with the mantle beneath Agrigan at fO 2 s of ΔQFM +1 to +1.6, significantly more oxidized than current constraints for the mantle beneath midocean ridges.
The Crystal/Melt Partitioning of V during Mantle Melting as a Function of Oxygen Fugacity Compared with some other Elements
- Al, P, Ca, Sc, Ti, Cr, Fe, Ga, Y, Zr and Nb). Journal of Petrology
, 2009
"... Vanadium exists in multiple valence states in silicate and oxide systems, namelyV2þ,V3þ,V4þ and V5þ.This special characteristic has been exploited in several ways to estimate the redox conditions of high-temperature planetary processes, such as partial melting and core formation. However, the use of ..."
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Vanadium exists in multiple valence states in silicate and oxide systems, namelyV2þ,V3þ,V4þ and V5þ.This special characteristic has been exploited in several ways to estimate the redox conditions of high-temperature planetary processes, such as partial melting and core formation. However, the use of Vas a universal redox indicator (i.e. suitable for the entire range of oxygen fugacities found in the inner Solar System) requires precise knowledge of the partitioning of all of its several valence states. Here we report the results of a series of 1 atm (13008C) and high-pressure (1^3 GPa, 1315^ 14508C) experiments carried out over a range of redox conditions sufficiently large (from QFM133 to QFMþ114, where QFM is the quartz^fayalite^magnetite oxygen buffer) to constrain the full panoply of V chemical behaviour. Partition coefficients between the major upper-mantle minerals (olivine, clinopyroxene, orthopyroxene, spinel and garnet) and silicate melt were precisely measured with
Calibration of an Empirical Thermometer and Oxybarometer based on the Partitioning of Sc, Y and V between Olivine and Silicate Melt
- Journal of Petrology
, 2013
"... The evolution of basaltic magmas depends on their redox state, hence oxygen fugacity, but there is increasing evidence that this intensive thermodynamic variable may be less well understood in basalts than commonly supposed. The redox state of terrestrial basalts has to a large extent been inferred ..."
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The evolution of basaltic magmas depends on their redox state, hence oxygen fugacity, but there is increasing evidence that this intensive thermodynamic variable may be less well understood in basalts than commonly supposed. The redox state of terrestrial basalts has to a large extent been inferred from the Fe3þ/Fe2þ ratios of their quenched glasses. However, this quantity appears to be significantly affected during late and post-eruptive processes in magmatic systems (e.g. by degassing, charge-transfer reactions of redox-variable species, and al-teration), so that the degree to which the Fe3þ/Fe2þ ratios preserved in basaltic glasses reflect the oxidation state of the magma at high temperature is unclear. Because olivine is the first silicate mineral to crystallize from primitive basaltic liquids on cooling following de-compression, the equilibrium partitioning relations preserved in oliv-ine phenocrysts in basalts are, in principle, less disturbed by these late and post-eruptive processes and, therefore, may better reflect the
Discipline: Structure et Evolution de la Terre et des autres Planètes
, 2009
"... Imprégnation magmatique de la lithosphère océanique: Etude microstructurale et géochimique des séries gabbröıques forées a ̀ la dorsale Médio-Atlantique Marion Drouin To cite this version: ..."
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Imprégnation magmatique de la lithosphère océanique: Etude microstructurale et géochimique des séries gabbröıques forées a ̀ la dorsale Médio-Atlantique Marion Drouin To cite this version:
The stable vanadium isotope composition of the mantle and mafic lavas
"... V could relate to oxidation state and thus oxygen fugacity, further work is required to resolve the isotopic effects of oxidation state, partial melting, and mineral fractionation factors. ..."
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V could relate to oxidation state and thus oxygen fugacity, further work is required to resolve the isotopic effects of oxidation state, partial melting, and mineral fractionation factors.
Discipline: Structure et évolution de la Terre et des autres planètes
, 2012
"... Interaction entre deformation et percolation de magma ou de fluide dans le manteau a ̀ l’aplomb des zones de subduction Vincent Soustelle To cite this version: Vincent Soustelle. Interaction entre deformation et percolation de magma ou de fluide dans le manteau a ̀ l’aplomb des zones de subduction. ..."
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Interaction entre deformation et percolation de magma ou de fluide dans le manteau a ̀ l’aplomb des zones de subduction Vincent Soustelle To cite this version: Vincent Soustelle. Interaction entre deformation et percolation de magma ou de fluide dans le manteau a ̀ l’aplomb des zones de subduction. Tectonique. Universite de Montpellier 2, 2010. Français. <tel-00689832> HAL Id: tel-00689832
The Role of Water in Generating the Calc-alkalineTrend: NewVolatile Data for Aleutian Magmas and a NewTholeiitic Index
, 2010
"... The origin of tholeiitic (TH) versus calc-alkaline (CA) magmatic trends has long been debated. Part of the problem stems from the lack of a quantitative measure for the way in which a magma evolves. Recognizing that the salient feature in manyTH^CA discrimination diagrams is enrichment in Fe during ..."
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The origin of tholeiitic (TH) versus calc-alkaline (CA) magmatic trends has long been debated. Part of the problem stems from the lack of a quantitative measure for the way in which a magma evolves. Recognizing that the salient feature in manyTH^CA discrimination diagrams is enrichment in Fe during magma evolution, we have developed a quantitative index of Fe enrichment, the Tholeiitic Index (THI):THIFe4·0/Fe8·0, where Fe4·0 is the average FeO* concentration of samples with 41wt % MgO, and Fe8·0 is the average FeO * at 81wt % MgO. Magmas withTHI41 have enriched in FeO * during differentiation from basalts to andesites and are tholeiitic; magmas with THI51 are calc-alkaline. Most subduction zone volcanism is CA, but to varying extents; the THI expresses the continuum of Fe enrichment observed in magmatic suites in all tectonic settings.To test various controls on the develop-ment of CA trends, we present new magmatic water measurements
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"... ew ge, long-term sea level serpentinite at ima y a ag ts o pr rcs er to construct a model of the deep Earth water cycle. The simulation is con-rth's in n and c tion zo volcani bound water in sediments, altered oceanic crust and serpentinized lith- on calculations of the equilibrium stability of ..."
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ew ge, long-term sea level serpentinite at ima y a ag ts o pr rcs er to construct a model of the deep Earth water cycle. The simulation is con-rth's in n and c tion zo volcani bound water in sediments, altered oceanic crust and serpentinized lith- on calculations of the equilibrium stability of hydrous phases at sub-
