ORCID Profile
0000-0003-1038-7301
Current Organisation
University of Oxford
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Publisher: Mineralogical Society of America
Date: 07-2022
DOI: 10.2138/AM-2021-7682
Abstract: We performed a series of experiments at 1 atm pressure and temperatures of 1300–1500 °C to determine the effect of oxygen fugacity on the oxidation state of Fe in a synthetic martian basalt. Ferricferrous ratios were determined on the quenched glasses using Mössbauer spectroscopy. Following the conventional doublet assignments in the spectrum, we obtain a Fe3+/ΣFe value of 0.19 at 1450 °C and an oxygen fugacity corresponding to the QFM buffer. If we apply the Berry et al. (2018) assignments the calculated Fe3+/ΣFe drops to 0.09, and the slope of log(XFeO1.5melt/XFeOmelt) vs. log(fO2) changes from 0.18 to 0.26. Combining oxidation state data together with results of one additional olivine-bearing experiment to determine the appropriate value(s) for the olivine (Ol)-liquid (liq) exchange coefficient, KD,Fe2+-Mg = (FeO/MgO)Ol/(FeO/MgO)liq (by weight), suggests a KD,Fe2+-Mg of 0.388 ± 0.006 (uncertainty is one median absolute deviation) using the traditional interpretation of Mössbauer spectroscopy and a value of 0.345 ± 0.005 following the Mössbauer spectra approach of Berry et al. (2018). We used our value of KD,Fe2+-Mg to test whether any of the olivine-bearing shergottites represent liquids. For each meteorite, we assumed a liquid composition equal to that of the bulk and then compared that liquid to the most Mg-rich olivine reported. Applying a KD,Fe2+-Mg of ~0.36 leads to the possibility that bulk Yamato 980459, NWA 5789, NWA 2990, Tissint, and EETA 79001 (lithology A) represent liquids.
Publisher: Mineralogical Society of America
Date: 05-2023
DOI: 10.2138/AM-2022-8450
Abstract: We have performed experiments at 1.5 GPa and 1400 °C on 25 different bulk compositions to determine the effects of major element compositions on the Cl contents of silicate melts at known fugacities of Cl2 and O2. The experimental method involved mixing a “sliding” Cl buffer, a mixture of AgCl, AgI, and Ag with the silicate bulk composition and performing the experiment in a graphite capsule together with a source of CO2 (AgCO3). The graphite capsules were sealed inside welded Pt tubes to maintain a CO2-CO atmosphere with oxygen fugacity fixed at the C-CO-CO2 (CCO) buffer. During the experiment, the Cl buffer segregates leaving a Cl-bearing melt, which quenches to a glass. We used the results to define chloride capacity CCl for each melt at the pressure and temperature of the experiment: C Cl = Cl ( wt% ) f ( Cl 2 ) + f O 2 4 Chloride capacity was found to correlate positively with optical basicity and NBO/T and negatively with ionic porosity and the Larsen index. We combined our new data with the results of Thomas and Wood (2021) to derive an equation describing the composition, pressure and temperature dependence of the chloride capacity: log C C l = 1.604 + ( 4470 X C a − 3430 X S i + 2592 X F e − 4092 X K − 894 P ) / T . In this equation, XCa, XSi, and so on refer to the oxide mole fractions on a single-cation basis, P is in GPa and T in K. The equation reproduces 58 data points with an r2 of 0.96 and a standard error of 0.089. The addition of literature data on hydrous experiments indicates that the effects of & .3 wt% H2O are small enough to be ignored. We also performed experiments aimed at determining the conditions of NaCl saturation in melts. When combined with literature data we obtained: log ( C l − ) = log ( a N a C l ) + 0.06 − ( 2431 X C a + 3430 X S i − 2592 X F e + 3484 X N a + 4092 X K − 2417 ) / T where (Cl–) is the Cl content of the melt in wt% aNaCl is the activity of NaCl (liquid) and the other symbols are the same as before. The results indicate that basalt dissolves ~8 times more Cl than rhyolite at a given NaCl activity i.e., Cl is ~8 times more soluble in basalt than in rhyolite.
Publisher: Elsevier BV
Date: 11-2020
Publisher: Elsevier BV
Date: 11-2022
Publisher: Springer Science and Business Media LLC
Date: 08-2023
DOI: 10.1007/S00410-023-02033-9
Abstract: We have determined the solubility of sulfur (S) as sulfide (S 2– ) for 13 different natural melt compositions at temperatures of 1473–1773 K under controlled conditions of oxygen and sulfur fugacities ( f O 2 and f S 2 , respectively). The S and major element contents of the quenched glasses were determined by electron microprobe. The sulfide capacity parameter (C S2– ) was used to express S 2– solubility as a function of the oxygen and sulfur fugacities according to the equation: $$\\log C_{{S^{2 - } }} = \\log S_{melt} \\left( {wt\\% } \\right) + 0.5\\log \\left( {\\frac{{fO_{2} }}{{fS_{2} }}} \\right)$$ log C S 2 - = log S melt w t % + 0.5 log f O 2 f S 2 . Sulfide capacities of silicate melts were found to increase with temperature and the FeO content of the melt. We combined our sulfide data at 1473–1773 K with (O’Neill and Mavrogenes, J Petrol 43:1049–1087, 2002) results at 1673 K, and obtained by stepwise linear regression the following equation for sulfide capacity $$\\log C_{{S^{2 - } }} = 0.225 + \\left( {25237X_{FeO} + 5214X_{CaO} + 12705X_{MnO} + 19829X_{{K_{2} O}} - 1109X_{{Si_{0.5} O}} - 8879} \\right)/T{ }$$ log C S 2 - = 0.225 + 25237 X FeO + 5214 X CaO + 12705 X MnO + 19829 X K 2 O - 1109 X S i 0.5 O - 8879 / T . X MO is the mole fraction of the oxide of M on a single-oxygen basis, and T is in Kelvin. The sulfide capacity equation was combined with sulfate capacity (C S6+ ) data for similar compositions and at the same temperatures (Boulliung and Wood, Geochim Cosmochim Acta 336:150–164, 2022), to estimate the S redox state (S 6+ /S 2– ratio) as a function of melt composition, temperature and oxygen fugacity. Results obtained are in good agreement with earlier measurements of S 6+ /S 2– for basaltic and andesitic compositions. We observe a significant increase, however, relative to FMQ of the oxygen fugacity of the S 2– to S 6+ transition as temperature is lowered from 1773 to 1473 K. We used our results to simulate sulfur-degassing paths for basaltic compositions under various redox conditions (FMQ –2 log f O 2 units to FMQ + 2). The calculations indicate that, given an initial concentration of 0.12 wt% S in an ascending melt at 250 MPa, most of the S ( 80%) will be degassed before the magma reaches 100 MPa pressure.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Bernard Wood.