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Experimental calibration of vanadium partitioning and stable isotope fractionation between hydrous granitic melt and magnetite at 800 °C and 0.5 GPa

Sossi, P.A.; Prytulak, J.; O’Neill, H. St. C.

Experimental calibration of vanadium partitioning and stable isotope fractionation between hydrous granitic melt and magnetite at 800 °C and 0.5 GPa Thumbnail


Authors

P.A. Sossi

H. St. C. O’Neill



Abstract

Vanadium has multiple oxidation states in silicate melts and minerals, a property that also promotes fractionation of its isotopes. As a result, vanadium isotopes vary during magmatic differentiation, and can be powerful indicators of redox processes at high temperatures if their partitioning behaviour can be determined. To quantify the partitioning and isotope fractionation factor of V between magnetite and melt, piston cylinder experiments were performed in which magnetite and a hydrous, haplogranitic melt were equilibrated at 800 °C and 0.5 GPa over a range of oxygen fugacities ( fO2), bracketing those of terrestrial magmas. Magnetite is isotopically light with respect to the coexisting melt, a tendency ascribed to the VI-fold V3+ and V4+ in magnetite, and a mixture of IV- and VI-fold V5+ and V4+ in the melt. The magnitude of the fractionation factor systematically increases with increasing log fO2 relative to the Fayalite–Magnetite–Quartz buffer (FMQ), from ∆51Vmag-gl = − 0.63 ± 0.09‰ at FMQ − 1 to − 0.92 ± 0.11‰ (SD) at ≈ FMQ + 5, reflecting constant V3+/V4+ in magnetite but increasing V5+/V4+ in the melt with increasing log fO2. These first mineral-melt measurements of V isotope fractionation factors underline the importance of both oxidation state and co-ordination environment in controlling isotopic fractionation. The fractionation factors determined experimentally are in excellent agreement with those needed to explain natural isotope variations in magmatic suites. Furthermore, these experiments provide a useful framework in which to interpret vanadium isotope variations in natural rocks and magnetites, and may be used as a potential fingerprint the redox state of the magma from which they crystallise.

Citation

Sossi, P., Prytulak, J., & O’Neill, H. S. C. (2018). Experimental calibration of vanadium partitioning and stable isotope fractionation between hydrous granitic melt and magnetite at 800 °C and 0.5 GPa. Contributions to Mineralogy and Petrology, 173(4), Article 27. https://doi.org/10.1007/s00410-018-1451-8

Journal Article Type Article
Acceptance Date Feb 15, 2018
Online Publication Date Mar 12, 2018
Publication Date Apr 1, 2018
Deposit Date Apr 24, 2018
Publicly Available Date Mar 12, 2019
Journal Contributions to Mineralogy and Petrology
Print ISSN 0010-7999
Electronic ISSN 1432-0967
Publisher Springer
Peer Reviewed Peer Reviewed
Volume 173
Issue 4
Article Number 27
DOI https://doi.org/10.1007/s00410-018-1451-8

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