Micro-XANES measurements on experimental spinels and the oxidation state of vanadium in coexisting spinel and silicate melt
- NASA
We show that experimental spinels coexisting with silicate melt always have lower valence vanadium, and that spinels typically have 3+, whereas the coexisting melt has 4+ or 5+. Implications of these results for planetary basalts will be discussed. Spinel can be a significant host phase for V which has multiple oxidation states V{sup 2+}, V{sup 3+}, V{sup 4+} or V{sup 5+} at oxygen fugacities relevant to natural systems. The magnitude of D(V) spinel/melt is known to be a function of composition, temperature and fO{sub 2}, but the uncertainty of the oxidation state under the range of natural conditions has made elusive a thorough understanding of D(V) spinel/melt. For example, V{sup 3+} is likely to be stable in spinels, based on exchange with Al in experiments in the CaO-MgO-Al{sub 2}O{sub 3}-SiO{sub 2} system. On the other hand, it has been argued that V{sup 4+} will be stable across the range of natural oxygen fugacities in nature. In order to build on our previous work in more oxidized systems, we have carried out experiments at relatively reducing conditions from the FMQ buffer to 2 log fO{sub 2} units below the IW buffer. These spinel-melt pairs, where V is present in the spinel at natural levels ({approx}300 ppm V), were analyzed using an electron microprobe at NASA-JSC and mi-cro-XANES at the Advanced Photon Source at Argonne National Laboratory. The new results will be used together with previous results to understand the valence of V in spinel-melt systems across 12 orders of magnitude of oxygen fugacity, and with application to natural systems.
- Research Organization:
- Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1008945
- Country of Publication:
- United States
- Language:
- ENGLISH
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