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Oxidation in CSPV experiments involving H2O-bearing mafic magmas: Quantification and mitigation

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Published/Copyright: March 7, 2015
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American Mineralogist
From the journal American Mineralogist Volume 98 Issue 7

Abstract

A difficulty in performing high-temperature (>900 °C) experiments on near-liquidus hydrous mafic melts in gas-medium cold-seal pressure vessels (CSPV) is the tendency for H2O in the fluid phase to dissociate and H2 to diffuse through capsule material, leading to progressive oxidation of sample material. Negative consequences include premature stabilization of Fe-Ti oxide phases and commensurate deviation of the liquid line of descent toward silica enrichment. Moreover, time-variance of an intensive variable equal in importance to temperature or total pressure is an unwanted feature of any experimental study. Methodologies commonly employed to mitigate the oxidation problem, not without their own drawbacks, include incorporating CH4 into the pressurizing gas, limiting run duration to 24 h, enclosing samples in Au-alloy capsules, and incorporating solid buffering assemblages to serve as indicators of fO₂ excursion. Using the Co-Pd-O system as a fO₂ sensor, we investigated progressive oxidation of basaltic andesite at 1010 °C and PH₂O = 150 MPa. Our time-series of 12, 24, 36, 48, and 60 h run durations reveals that oxidation occurs at a very high rate (~3-4 log unit change in fO₂ in 48 h). Both the variability of fO₂ and magnitude of dehydration-oxidation are considered unacceptable for phase equilibria work. Incorporation of additional CH4 serves only to offset the progressive oxidation trend toward a lower absolute range in fO₂. Ultimately, rapid oxidation in CSPV hinders the chemical equilibration of experimental charges. To mitigate the issue, we propose the following solution: Incorporation of a substantial mass of Ni metal powder as an O2 getter to the outer capsule successfully: (1) slows down oxidation; (2) stabilizes fO₂ at the nickel-nickel oxide (NNO) buffer after ~20 h; and (3) allows compositions to approach equilibrium. Runs much longer than 48 h may require one or more steps involving quenching and re-filling the pressure system with CH4.

Keywords: Experimental petrology; oxygen fugacity; rates of oxidation; crystallization; chemical equilibrium
Received: 2012-6-3
Accepted: 2013-2-7
Published Online: 2015-3-7
Published in Print: 2013-7-1

© 2015 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am.2013.4253
Keywords for this article
Experimental petrology; oxygen fugacity; rates of oxidation; crystallization; chemical equilibrium

Articles in the same Issue

  1. Highlights and Breakthroughs. A step closer to predicting the bonding geometry of crystals
  2. Minerals in the Human. Body Crystal chemistry of cement-asbestos
  3. Versatile monazite: Resolving geological records and solving challenges in materials science. Microprobe analysis and dating of monazite from the Potsdam Formation, New York: A progressive record of chemical reaction and fluid interaction
  4. A study of ruby (corundum) compositions from the Mogok Belt, Myanmar: Searching for chemical fingerprints
  5. The dehydroxylation of chrysotile: A combined in situ micro-Raman and micro-FTIR study
  6. Synchrotron Mössbauer study of Fe-bearing pyrope at high pressures and temperatures
  7. In situ Raman spectroscopic study of transient polyhedral distortions during cesium ion exchange into sitinakite
  8. A micro-reflectance IR spectroscopy method for analyzing volatile species in basaltic, andesitic, phonolitic, and rhyolitic glasses
  9. Fundamental Mössbauer parameters of synthetic Ca-Mg-Fe pyroxenes
  10. Iron oxidation state in phyllosilicate single crystals using Fe-K pre-edge and XANES spectroscopy: Effects of the linear polarization of the synchrotron X-ray beam
  11. Effect of particle size on phase transitions in metastable alumina nanoparticles: A view from high-resolution solid-state 27Al NMR study
  12. Magnesite formation from MgO and CO2 at the pressures and temperatures of Earth’s mantle
  13. Investigation of the hydrozincite structure by infrared and solid-state NMR spectroscopy
  14. Local structure in C2/c clinopyroxenes on the hedenbergite (CaFeSi2O6)-ferrosilite (Fe2Si2O6) join: A new interpretation for the Mössbauer spectra of Ca-rich C2/c clinopyroxenes and implications for pyroxene exsolution
  15. On the effect of carbonate on barite growth at elevated temperatures
  16. The structure of (Ca,Co)CoSi2O6 pyroxenes and the Ca-M2+ substitution in (Ca,M2+)M2+Si2O6 pyroxenes (M2+ = Co, Fe, Mg)
  17. Structure of mixed-layer corrensite-chlorite revealed by high-resolution transmission electron microcopy (HRTEM)
  18. In situ dehydration behavior of veszelyite (Cu,Zn)2Zn(PO4)(OH)3-2H2O: A single-crystal X-ray study
  19. Ab-initio determination of high-pressure and high-temperature thermoelastic and thermodynamic properties of low-spin (Mg1–xFex)O ferropericlase with x in the range [0.06, 0.59]
  20. The composite modulated structure of cupropearceite and cupropolybasite and its behavior toward low temperature
  21. Oxidation in CSPV experiments involving H2O-bearing mafic magmas: Quantification and mitigation
  22. Coexisting hydroxyl groups and H2O molecules in minerals: A single-crystal neutron diffraction study of eosphorite, MnAlPO4(OH)2·H2O
  23. Rapidcreekite in the sulfuric acid weathering environment of Diana Cave, Romania
  24. Terrywallaceite, AgPb(Sb,Bi)3S6, isotypic with gustavite, a new mineral from Mina Herminia, Julcani Mining District, Huancavelica, Peru
  25. Lead-tellurium oxysalts from Otto Mountain near Baker, California: X. Bairdite, Pb2Cu42+Te26+O10(OH)2(SO4)(H2O), a new mineral with thick HCP layers
  26. Lusernaite-(Y), Y4Al(CO3)2(OH,F)11·6H2O, a new mineral species from Luserna Valley, Piedmont, Italy: Description and crystal structure
  27. Fe-rich and As-bearing vesuvianite and wiluite from Kozlov, Czech Republic
  28. WinPyrox: A Windows program for pyroxene calculation classification and thermobarometry
  29. Further work on experimental plagioclase equilibria and the Skaergaard liquidus temperature
  30. Leter. Discovery of dmisteinbergite (hexagonal CaAl2Si2O8) in the Allende meteorite: A new member of refractory silicates formed in the solar nebula
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