Stable vanadium isotopes as a redox proxy in magmatic systems

J. Prytulak; P. A. Sossi; A. N. Halliday; T. Plank; P. S. Savage; J. D. Woodhead

doi:10.7185/geochemlet.1708

Stable vanadium isotopes as a redox proxy in magmatic systems

J. Prytulak, P. A. Sossi, A. N. Halliday, T. Plank, P. S. Savage, J. D. Woodhead

Research output: Contribution to journal › Article › peer-review

Abstract

Recycling pathways of multivalent elements, that impact our understanding of diverse geological processes from ore formation to the rise of atmospheric oxygen, depend critically on the spatial and temporal variation of oxygen fugacity (fO₂) in the Earth’s interior. Despite its importance, there is currently no consensus on the relative fO₂ of the mantle source of mid-ocean ridge basalts compared to the sub-arc mantle, regions central to the mediation of crust-mantle mass balances. Here we present the first stable vanadium isotope measurements of arc lavas, complemented by non-arc lavas and two co-genetic suites of fractionating magmas, to explore the potential of V isotopes as a redox proxy. Vanadium isotopic compositions of arc and non-arc magmas with similar MgO overlap with one another. However, V isotopes display strikingly large, systematic variations of ~2 ‰ during magmatic differentiation in both arc and non-arc settings. Calculated bulk V Rayleigh fractionation factors (1000 lnα_min-melt of -0.4 to -0.5 ‰) are similar regardless of the oxidation state of the evolving magmatic system, which implies that V isotope fractionation is most influenced by differences in bonding environment between minerals and melt rather than changes in redox conditions. Thus, although subtle fO₂ effects may be present, V isotopes are not a direct proxy for oxygen fugacity in magmatic systems.

Original language	English
Number of pages	5
Journal	Geochemical Perspectives Letters
Volume	3
Issue number	1
DOIs	https://doi.org/10.7185/geochemlet.1708
Publication status	Published - 26 Oct 2016

Keywords

Vanadium
Stable isotopes
Magmatic fractionation
Oxygen fugacity
Magnetite

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© 2016 The Authors. This work is distributed under the Creative Commons Attribution 4.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Additional information is available at http://www. geochemicalperspectivesletters.org/copyright-and-permissions.
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title = "Stable vanadium isotopes as a redox proxy in magmatic systems",

abstract = "Recycling pathways of multivalent elements, that impact our understanding of diverse geological processes from ore formation to the rise of atmospheric oxygen, depend critically on the spatial and temporal variation of oxygen fugacity (fO2) in the Earth{\textquoteright}s interior. Despite its importance, there is currently no consensus on the relative fO2 of the mantle source of mid-ocean ridge basalts compared to the sub-arc mantle, regions central to the mediation of crust-mantle mass balances. Here we present the first stable vanadium isotope measurements of arc lavas, complemented by non-arc lavas and two co-genetic suites of fractionating magmas, to explore the potential of V isotopes as a redox proxy. Vanadium isotopic compositions of arc and non-arc magmas with similar MgO overlap with one another. However, V isotopes display strikingly large, systematic variations of ~2 ‰ during magmatic differentiation in both arc and non-arc settings. Calculated bulk V Rayleigh fractionation factors (1000 lnαmin-melt of -0.4 to -0.5 ‰) are similar regardless of the oxidation state of the evolving magmatic system, which implies that V isotope fractionation is most influenced by differences in bonding environment between minerals and melt rather than changes in redox conditions. Thus, although subtle fO2 effects may be present, V isotopes are not a direct proxy for oxygen fugacity in magmatic systems. ",

keywords = "Vanadium, Stable isotopes, Magmatic fractionation, Oxygen fugacity, Magnetite",

author = "J. Prytulak and Sossi, {P. A.} and Halliday, {A. N.} and T. Plank and Savage, {P. S.} and Woodhead, {J. D.}",

note = "JP was funded by NERC postdoctoral fellowship NE/H01313X/2, with support of the Oxford laboratories from an Advanced ERC grant (NEWISOTOPEGEOSCIENCE) to ANH. PAS by an APA PhD scholarship and ANU Vice-Chancellor{\textquoteright}s Scholarship.",

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doi = "10.7185/geochemlet.1708",

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AU - Prytulak, J.

AU - Sossi, P. A.

AU - Halliday, A. N.

AU - Plank, T.

AU - Savage, P. S.

AU - Woodhead, J. D.

N1 - JP was funded by NERC postdoctoral fellowship NE/H01313X/2, with support of the Oxford laboratories from an Advanced ERC grant (NEWISOTOPEGEOSCIENCE) to ANH. PAS by an APA PhD scholarship and ANU Vice-Chancellor’s Scholarship.

PY - 2016/10/26

Y1 - 2016/10/26

N2 - Recycling pathways of multivalent elements, that impact our understanding of diverse geological processes from ore formation to the rise of atmospheric oxygen, depend critically on the spatial and temporal variation of oxygen fugacity (fO2) in the Earth’s interior. Despite its importance, there is currently no consensus on the relative fO2 of the mantle source of mid-ocean ridge basalts compared to the sub-arc mantle, regions central to the mediation of crust-mantle mass balances. Here we present the first stable vanadium isotope measurements of arc lavas, complemented by non-arc lavas and two co-genetic suites of fractionating magmas, to explore the potential of V isotopes as a redox proxy. Vanadium isotopic compositions of arc and non-arc magmas with similar MgO overlap with one another. However, V isotopes display strikingly large, systematic variations of ~2 ‰ during magmatic differentiation in both arc and non-arc settings. Calculated bulk V Rayleigh fractionation factors (1000 lnαmin-melt of -0.4 to -0.5 ‰) are similar regardless of the oxidation state of the evolving magmatic system, which implies that V isotope fractionation is most influenced by differences in bonding environment between minerals and melt rather than changes in redox conditions. Thus, although subtle fO2 effects may be present, V isotopes are not a direct proxy for oxygen fugacity in magmatic systems.

AB - Recycling pathways of multivalent elements, that impact our understanding of diverse geological processes from ore formation to the rise of atmospheric oxygen, depend critically on the spatial and temporal variation of oxygen fugacity (fO2) in the Earth’s interior. Despite its importance, there is currently no consensus on the relative fO2 of the mantle source of mid-ocean ridge basalts compared to the sub-arc mantle, regions central to the mediation of crust-mantle mass balances. Here we present the first stable vanadium isotope measurements of arc lavas, complemented by non-arc lavas and two co-genetic suites of fractionating magmas, to explore the potential of V isotopes as a redox proxy. Vanadium isotopic compositions of arc and non-arc magmas with similar MgO overlap with one another. However, V isotopes display strikingly large, systematic variations of ~2 ‰ during magmatic differentiation in both arc and non-arc settings. Calculated bulk V Rayleigh fractionation factors (1000 lnαmin-melt of -0.4 to -0.5 ‰) are similar regardless of the oxidation state of the evolving magmatic system, which implies that V isotope fractionation is most influenced by differences in bonding environment between minerals and melt rather than changes in redox conditions. Thus, although subtle fO2 effects may be present, V isotopes are not a direct proxy for oxygen fugacity in magmatic systems.

KW - Vanadium

KW - Stable isotopes

KW - Magmatic fractionation

KW - Oxygen fugacity

KW - Magnetite

U2 - 10.7185/geochemlet.1708

DO - 10.7185/geochemlet.1708

M3 - Article

SN - 2410-339X

VL - 3

JO - Geochemical Perspectives Letters

JF - Geochemical Perspectives Letters

IS - 1

ER -

Stable vanadium isotopes as a redox proxy in magmatic systems

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Keywords

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