期刊
LITHOS
卷 358, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.lithos.2020.105404
关键词
Native vanadium; Super-reducing conditions; Mantle xenoliths; Immiscible melts; Mantle-derived methane; Mantle-derived hydrogen
资金
- DEST Systemic Infrastructure Grants
- ARC LIEF
- NCRIS/AuScope
- Macquarie University
- MIUR-PRIN2017 [2017AK8C32]
- University of Western Australia
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. Microstructures suggest that vanadium melts became immiscible with the host Ca-Al-Mg-Si-O melt, and nucleated as droplets on the surfaces of the oxide phases, principally hibonite. Many extended outward as rods or branching structures as the host oxide crystal grew. The stability of V-0 implies oxygen fugacities >= 9 log units below the Iron-Wustite buffer, suggesting a hydrogendominated atmosphere. This is supported by wt%-levels of hydrogen in gasses released by crushing, by Raman spectroscopy, and by the presence of VH2 among the vanadium balls. The oxide assemblage formed at 1400-1200 degrees C; the solution of hydrogen in the metal could lower the melting point of vanadium to these temperatures. These assemblages probably resulted from reaction between differentiated mafic melts and mantle-derived CH4 + H-2 fluids near the crust-mantle boundary, and they record the most reducing magmatic conditions yet documented on Earth. (C) 2020 Elsevier B.V. All rights reserved.
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