Valence state partitioning of V between pyroxene‐melt: Effects of pyroxene and melt composition,and direct determination of V valence states by XANES. Application to Martian basalt QUE 94201 composition |
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| Authors: | J M KARNER J J PAPIKE S R SUTTON C K SHEARER P BURGER G McKAY L LE |
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| Institution: | 1. Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA;2. Department of Geophysical Sciences, University of Chicago, Chicago, Illinois 60637, USA;3. Consortium for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, USA;4. Mail Code ST, NASA JSC, Houston, Texas 77058, USA;5. ESC Group, JE23, Houston, Texas 77058, USA |
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| Abstract: | Abstract— Experiments on a Martian basalt composition show that Dv augite/melt is greater than Dv pigeonite/melt in samples equilibrated under the same fO2 conditions. This increase is due to the increased availability of elements for coupled substitution with the V3+ or V4+ ions, namely A1 and Na. For this bulk composition, both A1 and Na are higher in concentration in augite compared with pigeonite; therefore more V can enter augite than pigeonite. Direct valence state determination by XANES shows that the V3+ and V4+ are the main V species in the melt at fO2 conditions of IW‐1 to IW+3.5, whereas pyroxene grains at IW‐1, IW, and IW+1 contain mostly V3+. This confirms the idea that V3+ is more compatible in pyroxene than V4+. The XANES data also indicates that a small percentage of V2+ may exist in melt and pyroxene at IW‐1. The similar valence of V in glass and pyroxene at IW‐1 suggests that V2+ and V3+ may have similar compatibilities in pyroxene. |
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