Mechanism and kinetics of reduction of a FeO-Fe2O3-CaO-MgO aluminosilicate melt in a high-CO-activity environment

Cooper, R. F.; Everman, Rebecca L.A.; Hustoft, J. W.; Shim, Sang‐Heon

doi:10.2138/am.2010.3375

Cited by 13 publications

(10 citation statements)

References 63 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Hence, the redox profiles determined for the basaltic andesite side of the diffusion couples may represent minimum gradients for the 1 hr and the 10 hr experiments, while it probably closely reflects the prevailing redox conditions of the melt in close proximity to the respective crystal pair for the 79 hr experiment. The proposed mechanism is consistent with theoretical considerations of Evans (2006) and studies of redox processes in Fe-bearing magnesium aluminosilicate glasses, and basaltic glasses and melts (e.g., Cooper et al, 1996Cooper et al, , 2010 …”

Section: Discussion Of the Redox Mechanismsupporting

confidence: 81%

“…S-A3) indicate that compatible elements are added to the melt near the interface, inducing a diffusive flux from mafic to felsic magma. Mass transfer of cations, and, in particular, of divalent network modifying cations, requires a counter flux of charge-compensating electron holes (h • , where the superscript dot indicates a single positive charge), which are the dominant mobile electronic species in Fe-bearing silicate melts (e.g., Cooper et al, 2010;Cooper, 2017). (t,x) is the relative change in electron holes (mol/100 g) at a distance x to the interface and at a time t integrated diffusive flux, thus, the sum of the concentration differences for each element i with the oxidation state n (e.g., n = +1 for Na and n = -1 for Cl) from its initial concentration (c t,x -c 0 ).…”

Section: Discussion Of the Redox Mechanismmentioning

confidence: 99%

“…Cooper et al, 2010). This hypothesis can be tested by performing simplified model calculations that consider the relative changes in melt composition on both sides of the diffusion couple as a function of distance to the interface, while ignoring simultaneous electron hole equilibration (h • gradients predict an electron hole enrichment zone (oxidation) in the basaltic andesite near the interface, and an electron hole depletion zone (reduction) in the dacite, mimicking the measured redox variations.…”

Section: Discussion Of the Redox Mechanismmentioning

confidence: 99%

See 2 more Smart Citations

A magma mixing redox trap that moderates mass transfer of sulphur and metals

Fiege¹,

Ruprecht²,

Simon³

2017

Geochem. Persp. Let.

View full text Add to dashboard Cite

doi: 10.7185/geochemlet.1722Mixing and juxtaposition of chemically distinct magmatic systems are key processes for the evolution of Earth's crust. Yet, the physicochemical nature at mixing interfaces remains poorly described, as crystallisation, melting, heat transfer, and diffusion are interconnected and lead to complex mass transfer processes driving unique patterns of element fractionation. Here, we use diffusion couple experiments between felsic and mafic magmas (melt + crystals ± volatiles) to document the formation of large gradients in oxygen fugacity at the magmamagma mixing interface. Reducing and oxidising boundary layers at the interface develop rapidly and remain in dynamic disequilibrium for days to possibly weeks. We suggest that the observed transient redox gradient is caused by cation transfer across the interface where the required counter flux of electron holes is insufficient to compensate an evolving electron hole gradient. Such boundary layer redox effects may control fractionation of polyvalent and chalcophile elements and moderate, for example, Cu/Au ratios in arc-related porphyry ore deposits.

show abstract

Section: Discussion Of the Redox Mechanismsupporting

confidence: 81%

Section: Discussion Of the Redox Mechanismmentioning

confidence: 99%

Section: Discussion Of the Redox Mechanismmentioning

confidence: 99%

See 1 more Smart Citation

A magma mixing redox trap that moderates mass transfer of sulphur and metals

Fiege¹,

Ruprecht²,

Simon³

2017

Geochem. Persp. Let.

View full text Add to dashboard Cite

show abstract

“…The amount of ferric iron can be increased solely by quenching through redox couple reactions with other heterovalent ions present in the melt, specifically Ti 3+,4+ , ±S 2−,4+,6+ [ Paul , 1990; cf. Cooper et al , 2010]. Analysis of the relative changes in the activity coefficients of the ions with temperature change shows that the relative driving force for the oxidation of Fe 2+ versus Ti 3+ would increase at lower temperature, leading to the oxidation to Fe 3+ at the expense of Ti 4+ , again facilitating the nucleation of low‐Ti ferrites.…”

Section: Discussionmentioning

confidence: 99%

Effects of open and closed system oxidation on texture and magnetic response of remelted basaltic glass

Burgess

Cooper

Bowles

et al. 2010

Geochem Geophys Geosyst

View full text Add to dashboard Cite

[1] As part of an experimental and observational study of the magnetic response of submarine basaltic glass (SBG), we have examined, using ion backscattering spectrometry (RBS), transmission and scanning electron microscopy, energy dispersive X-ray spectrometry, and surface X-ray diffraction, the textures wrought by the controlled, open and closed system oxidation of glasses prepared by the controlled environment remelting and quenching of natural SBG. Initial compositions with ∼9 wt % FeO* were melted at 1430°C with the oxygen fugacity buffered at fayalite-magnetite-quartz; melts were cooled at a rate of 200°C min −1 near the glass transition (T g = 680°C). In open system experiments, where chemical exchange is allowed to occur with the surrounding atmosphere, polished pieces of glass were reheated to temperatures both below and above T g for times 1-5000 h; undercooled melts were oxidized at 900°C and 1200°C for 18 and 20 h, respectively. RBS demonstrates unequivocally that the dynamics of open system oxidation involves the outward motion of network-modifying cations. Oxidation results in formation of a Fe-, Ca-, and Mg-enriched surface layer that consists in part of Ti-free nanometer-scale ferrites; a divalentcation-depleted layer is observed at depths >1 mm. Specimens annealed/oxidized above T g have magnetizations elevated by 1-2 orders of magnitude relative to the as-quenched material; this does not appear to be related to the surface oxidation. Quenched glass (closed system, i.e., no chemical exchange between sample and atmosphere) exhibits very fine scale chemical heterogeneities that coarsen with time under an electron beam; this metastable amorphous immiscibility is the potential source for the nucleation of ferrites with a wide range of Ti contents, ferrites not anticipated from an equilibrium analysis of the bulk basalt composition.

show abstract

“…However, under more oxidizing conditions in basaltic melt compositions, carbon is dissolved as carbonate (17)(18)(19), and the transition in speciation from methane to carbonate has long been debated as either occurring at more reducing conditions than IW+1 (20, 21) or at more oxidizing conditions (15). Another study (22) shows that a significant amount of C 4+ (carbonate) can be incorporated at extremely low fO 2 (IW−4.5) if Fe and alkalis are present in the melt. Additional experiments on Fe-bearing basalt are clearly required to resolve the conflicts in existing data.…”

mentioning

confidence: 99%

Degassing of reduced carbon from planetary basalts

Wetzel

Rutherford

Jacobsen

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Degassing of planetary interiors through surface volcanism plays an important role in the evolution of planetary bodies and atmospheres. On Earth, carbon dioxide and water are the primary volatile species in magmas. However, little is known about the speciation and degassing of carbon in magmas formed on other planets (i.e., Moon, Mars, Mercury), where the mantle oxidation state [oxygen fugacity (fO 2 )] is different from that of the Earth. Using experiments on a lunar basalt composition, we confirm that carbon dissolves as carbonate at an fO 2 higher than -0.55 relative to the iron wustite oxygen buffer (IW-0.55), whereas at a lower fO 2 , we discover that carbon is present mainly as iron pentacarbonyl and in smaller amounts as methane in the melt. The transition of carbon speciation in mantle-derived melts at fO 2 less than IW-0.55 is associated with a decrease in carbon solubility by a factor of 2. Thus, the fO 2 controls carbon speciation and solubility in mantle-derived melts even more than previous data indicate, and the degassing of reduced carbon from Fe-rich basalts on planetary bodies would produce methane-bearing, CO-rich early atmospheres with a strong greenhouse potential.hydrogen | iron carbonyl | magmatic volatiles | experimental petrology M agmas formed through igneous processes on parent bodies in the early solar system span 12 log units in oxidation state, from 6.3 log units of oxygen fugacity (fO 2 ) below the iron wustite oxygen buffer (IW) to 6 log units above the IW (IW−6.3 to IW+6) (1-4). Over the wide range of basalt fO 2 observed in these planetary bodies, thermodynamic data for the C-O-H gas system indicate that there are significant changes in gas phase speciation (5). These differences should be reflected in how volatiles are dissolved in magmas, but carbon speciation experiments for basaltic systems are limited, particularly at low fO 2 . The developing evidence for volatiles in magmas erupted on the Moon (6, 7) as well as on Earth (3,8), Mars (9-12), and Mercury (13) is a strong incentive to improve our understanding of C-O-H speciation and solubility in planetary basaltic magmas.Previous experimental studies on the speciation of carbon in Fe-free silicate systems under reducing conditions or at fO 2 < IW show carbon is dissolved as methane (14-16). However, under more oxidizing conditions in basaltic melt compositions, carbon is dissolved as carbonate (17)(18)(19), and the transition in speciation from methane to carbonate has long been debated as either occurring at more reducing conditions than IW+1 (20, 21) or at more oxidizing conditions (15). Another study (22) shows that a significant amount of C 4+ (carbonate) can be incorporated at extremely low fO 2 (IW−4.5) if Fe and alkalis are present in the melt. Additional experiments on Fe-bearing basalt are clearly required to resolve the conflicts in existing data. The results are important in understanding the residence time of carbon in the mantle and the rate of carbon degassing during the early evolution of terrestrial planets ...

show abstract

Mechanism and kinetics of reduction of a FeO-Fe2O3-CaO-MgO aluminosilicate melt in a high-CO-activity environment

Cited by 13 publications

References 63 publications

A magma mixing redox trap that moderates mass transfer of sulphur and metals

A magma mixing redox trap that moderates mass transfer of sulphur and metals

Effects of open and closed system oxidation on texture and magnetic response of remelted basaltic glass

Degassing of reduced carbon from planetary basalts

Contact Info

Product

Resources

About