TY - JOUR
T1 - Extreme reduction
T2 - Mantle-derived oxide xenoliths from a hydrogen-rich environment
AU - Griffin, W. L.
AU - Gain, S. E. M.
AU - Camara, F.
AU - Bindi, L.
AU - Shaw, J.
AU - Alard, O.
AU - Saunders, M.
AU - Huang, J-X
AU - Toledo, V
AU - O'Reilly, S. Y.
PY - 2020/4
Y1 - 2020/4
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. 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.
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. 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.
KW - Immiscible melts
KW - Mantle xenoliths
KW - Mantle-derived hydrogen
KW - Mantle-derived methane
KW - Native vanadium
KW - Super-reducing conditions
UR - https://www.webofscience.com/api/gateway?GWVersion=2&SrcApp=anu_research_portal_plus2&SrcAuth=WosAPI&KeyUT=WOS:000528204700005&DestLinkType=FullRecord&DestApp=WOS_CPL
U2 - 10.1016/j.lithos.2020.105404
DO - 10.1016/j.lithos.2020.105404
M3 - Article
SN - 0024-4937
VL - 358
JO - Lithos
JF - Lithos
M1 - 105404
ER -