TY  - JOUR
A1  - Botcharnikov, Roman E.
A1  - Koepke, J.
A1  - Holtz, Francois
A1  - McCammon, C.
A1  - Wilke, Max
T1  - The oxidation and structural state of Fe in hydrous ferrobasaltic melt
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Botcharnikov, Roman E.
A1  - Koepke, J.
A1  - Holtz, Francois
A1  - McCammon, C.
A1  - Wilke, Max
T1  - The effect of water activity on the oxidation and structural state of Fe in a ferro-basaltic melt
N2  - Experimental investigations have been performed at T = 1200 degrees C, P = 200 MPa and fH(2) corresponding to H2O-MnO-Mn3O4 and H2O-QFM redox buffers to study the effect of H2O activity on the oxidation and structural state of Fe in an iron-rich basaltic melt. The analysis of Mossbauer and Fe K-edge X-ray absorption nearedge structure (XANES) spectra of the quenched hydrous ferrobasaltic glasses shows that the Fe3+/Sigma Fe ratio of the glass is directly related to aH(2)O in a H-2-buffered system and, consequently, to the prevailing oxygen fugacity (through the reaction of water dissociation H2O <-> H-2 + 1/2 O-2). However, water as a chemical component of the silicate melt has an indistinguishable effect on the redox state of iron at studied conditions. The experimentally obtained relationship between fO(2) and Fe3+/Fe2+ in the hydrous ferrobasaltic melt can be adequately predicted in the investigated range by the existing empiric and thermodynamic models. The ratio of ferric and ferrous Fe is proportional to the oxygen fugacity to the power of similar to 0.25 which agrees with the theoretical value from the stoichiometry of the Fe redox reaction (FeO + 1/4 O-2 = FeO1.5). The mean centre shifts for Fe2+ and Fe3+ absorption doublets in Mossbauer spectra show little change with increasing Fe3+/Sigma Fe, suggesting no significant change in the type of iron coordination. Similarly, XANES preedge spectra indicate a mixed (C3h, Td, and Oh, i.e., 5-, 4-, and sixfold) coordination of Fe in hydrous basaltic glasses. Copyright (c) 2005 Elsevier Ltd
Y1  - 2005
SN  - 0016-7037
ER  - 
TY  - JOUR
A1  - Benard, Antoine
A1  - Klimm, Kevin
A1  - Woodland, Alan B.
A1  - Arculus, Richard J.
A1  - Wilke, Max
A1  - Botcharnikov, Roman E.
A1  - Shimizu, Nobumichi
A1  - Nebel, Oliver
A1  - Rivard, Camille
A1  - Ionov, Dmitri A.
T1  - Oxidising agents in sub-arc mantle melts link slab devolatilisation and arc magmas
JF  - Nature Communications
N2  - Subduction zone magmas are more oxidised on eruption than those at mid-ocean ridges. This is attributed either to oxidising components, derived from subducted lithosphere (slab) and added to the mantle wedge, or to oxidation processes occurring during magma ascent via differentiation. Here we provide direct evidence for contributions of oxidising slab agents to melts trapped in the sub-arc mantle. Measurements of sulfur (S) valence state in sub-arc mantle peridotites identify sulfate, both as crystalline anhydrite (CaSO4) and dissolved SO42- in spinel-hosted glass (formerly melt) inclusions. Copper-rich sulfide precipitates in the inclusions and increased Fe3+/Sigma Fe in spinel record a S6+-Fe2+ redox coupling during melt percolation through the sub-arc mantle. Sulfate-rich glass inclusions exhibit high U/Th, Pb/Ce, Sr/Nd and delta S-34 (+ 7 to + 11%), indicating the involvement of dehydration products of serpentinised slab rocks in their parental melt sources. These observations provide a link between liberated slab components and oxidised arc magmas.
Y1  - 2018
U6  - https://doi.org/10.1038/s41467-018-05804-2
SN  - 2041-1723
VL  - 9
PB  - Nature Publ. Group
CY  - London
ER  -