Extreme reduction: vanadium melts in mantle-derived oxide xenoliths

W. L. Griffin, S. E. M. Gain, F. Cámara, L. Bindi, J. Shaw, Olivier Alard, M. Saunders, J.-X. Huang, V. Toledo, S. Y. O'Reilly

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Coarse-grained xenoliths of hibonite + grossite + Mg-Al-V spinel from Cretaceous pyroclastic rocks on Mt Carmel, N. Israel, and from Sierra de Comechingones, Argentina, include spherules, rods and dense branching structures of native vanadium and V-Al alloys. The microstructures suggest that vanadium melts became immiscible with the host Ca-Al-Mg-Si-O melt, which was already depleted in Fe and Si by the immiscible separation of Fe-Si-C silicide melts, and nucleated as droplets on the surfaces of the oxide phases, principally hibonite. Many extended outward into rods or branching structures as the host oxide crystal grew. The stability of V0 implies oxygen fugacities ≥9 log units below the Iron-Wustite buffer, suggesting a hydrogen-dominated atmosphere. This is supported by wt%-levels of hydrogen released by crushing hibonite grains, by Raman spectroscopy on the hibonite, and by the presence of VH2, the first natural hydride, among the vanadium balls. The oxide assemblage formed at 1400-1200 °C; the solution of hydrogen in the metal could lower the melting point of V0 to these temperatures. These assemblages probably resulted from reaction between differentiated mafic melts and mantle-derived CH4+H2 fluids near the crust-mantle boundary, and their fO2 record the most reducing magmatic conditions yet documented on Earth.

LanguageEnglish
Number of pages20
JournalEarth and Planetary Science Letters
Publication statusSubmitted - Sep 2019

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hibonite
Vanadium
vanadium
Oxides
Hydrogen
Earth mantle
melt
oxide
mantle
oxides
hydrogen
rods
spherules
crushing
Israel
Argentina
Crushing
crust-mantle boundary
Hydrides
spherule

Bibliographical note

Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

Cite this

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title = "Extreme reduction: vanadium melts in mantle-derived oxide xenoliths",
abstract = "Coarse-grained xenoliths of hibonite + grossite + Mg-Al-V spinel from Cretaceous pyroclastic rocks on Mt Carmel, N. Israel, and from Sierra de Comechingones, Argentina, include spherules, rods and dense branching structures of native vanadium and V-Al alloys. The microstructures suggest that vanadium melts became immiscible with the host Ca-Al-Mg-Si-O melt, which was already depleted in Fe and Si by the immiscible separation of Fe-Si-C silicide melts, and nucleated as droplets on the surfaces of the oxide phases, principally hibonite. Many extended outward into rods or branching structures as the host oxide crystal grew. The stability of V0 implies oxygen fugacities ≥9 log units below the Iron-Wustite buffer, suggesting a hydrogen-dominated atmosphere. This is supported by wt{\%}-levels of hydrogen released by crushing hibonite grains, by Raman spectroscopy on the hibonite, and by the presence of VH2, the first natural hydride, among the vanadium balls. The oxide assemblage formed at 1400-1200 °C; the solution of hydrogen in the metal could lower the melting point of V0 to these temperatures. These assemblages probably resulted from reaction between differentiated mafic melts and mantle-derived CH4+H2 fluids near the crust-mantle boundary, and their fO2 record the most reducing magmatic conditions yet documented on Earth.",
author = "Griffin, {W. L.} and Gain, {S. E. M.} and F. C{\'a}mara and L. Bindi and J. Shaw and Olivier Alard and M. Saunders and J.-X. Huang and V. Toledo and O'Reilly, {S. Y.}",
note = "Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.",
year = "2019",
month = "9",
language = "English",
journal = "Earth and Planetary Science Letters",
issn = "0012-821X",
publisher = "Elsevier",

}

Extreme reduction : vanadium melts in mantle-derived oxide xenoliths. / Griffin, W. L.; Gain, S. E. M.; Cámara, F.; Bindi, L.; Shaw, J.; Alard, Olivier; Saunders, M.; Huang, J.-X.; Toledo, V.; O'Reilly, S. Y.

In: Earth and Planetary Science Letters, 09.2019.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Extreme reduction

T2 - Earth and Planetary Science Letters

AU - Griffin, W. L.

AU - Gain, S. E. M.

AU - Cámara, F.

AU - Bindi, L.

AU - Shaw, J.

AU - Alard, Olivier

AU - Saunders, M.

AU - Huang, J.-X.

AU - Toledo, V.

AU - O'Reilly, S. Y.

N1 - Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

PY - 2019/9

Y1 - 2019/9

N2 - Coarse-grained xenoliths of hibonite + grossite + Mg-Al-V spinel from Cretaceous pyroclastic rocks on Mt Carmel, N. Israel, and from Sierra de Comechingones, Argentina, include spherules, rods and dense branching structures of native vanadium and V-Al alloys. The microstructures suggest that vanadium melts became immiscible with the host Ca-Al-Mg-Si-O melt, which was already depleted in Fe and Si by the immiscible separation of Fe-Si-C silicide melts, and nucleated as droplets on the surfaces of the oxide phases, principally hibonite. Many extended outward into rods or branching structures as the host oxide crystal grew. The stability of V0 implies oxygen fugacities ≥9 log units below the Iron-Wustite buffer, suggesting a hydrogen-dominated atmosphere. This is supported by wt%-levels of hydrogen released by crushing hibonite grains, by Raman spectroscopy on the hibonite, and by the presence of VH2, the first natural hydride, among the vanadium balls. The oxide assemblage formed at 1400-1200 °C; the solution of hydrogen in the metal could lower the melting point of V0 to these temperatures. These assemblages probably resulted from reaction between differentiated mafic melts and mantle-derived CH4+H2 fluids near the crust-mantle boundary, and their fO2 record the most reducing magmatic conditions yet documented on Earth.

AB - Coarse-grained xenoliths of hibonite + grossite + Mg-Al-V spinel from Cretaceous pyroclastic rocks on Mt Carmel, N. Israel, and from Sierra de Comechingones, Argentina, include spherules, rods and dense branching structures of native vanadium and V-Al alloys. The microstructures suggest that vanadium melts became immiscible with the host Ca-Al-Mg-Si-O melt, which was already depleted in Fe and Si by the immiscible separation of Fe-Si-C silicide melts, and nucleated as droplets on the surfaces of the oxide phases, principally hibonite. Many extended outward into rods or branching structures as the host oxide crystal grew. The stability of V0 implies oxygen fugacities ≥9 log units below the Iron-Wustite buffer, suggesting a hydrogen-dominated atmosphere. This is supported by wt%-levels of hydrogen released by crushing hibonite grains, by Raman spectroscopy on the hibonite, and by the presence of VH2, the first natural hydride, among the vanadium balls. The oxide assemblage formed at 1400-1200 °C; the solution of hydrogen in the metal could lower the melting point of V0 to these temperatures. These assemblages probably resulted from reaction between differentiated mafic melts and mantle-derived CH4+H2 fluids near the crust-mantle boundary, and their fO2 record the most reducing magmatic conditions yet documented on Earth.

M3 - Article

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

SN - 0012-821X

ER -