Temperature and pressure effects on the partitioning of V and Sc between clinopyroxene and silicate melt: Implications for mantle oxygen fugacity

Temperature and pressure effects on the partitioning of V and Sc between clinopyroxene and... AbstractThe partition coefficients of V and Sc between clinopyroxene and silicate melt (DVCpx/SMandDScCpx/SM)$\begin{array}{}(D \rm ^{Cpx/SM}_{V}\,and\,\it D \rm ^{Cpx/SM}_{Sc})\end{array}$ have been determined experimentally at 1200–1400 °C and 0.8–2.3 GPa, using a hornblende- and clinopyroxene-rich mantle rock in graphite-lined Pt95Rh05 capsules. The results show that the DVCpx/SM$\begin{array}{}D \rm ^{Cpx/SM}_{V}\end{array}$ and DScCpx/SM$\begin{array}{}D \rm ^{Cpx/SM}_{Sc}\end{array}$ values decrease from 3.8 to 2.3 and from 2.6 to 1.1, respectively, as the experimental temperature and pressure vary from 1200 °C and 0.8 GPa to 1400 °C and 2.3 GPa. The presence of water in silicate melts may also reduce DVCpx/SMandDScCpx/SM.$\begin{array}{}D \rm ^{Cpx/SM}_{V} and \,\it{D} \rm ^{Cpx/SM}_{Sc}.\end{array}$ These results imply that the effects of temperature, pressure, and melt water content on DVCpx/SM$\begin{array}{}D \rm ^{Cpx/SM}_{V}\end{array}$ should be considered when using V systematics in cratonic mantle peridotites to constrain cratonic mantle oxygen fugacity (fo2). However, although the dominant V in the present silicate melt is mixed V3+ and V4+, the DVCpx/SM/DScCpx/SM$\begin{array}{}D \rm ^{Cpx/SM}_{V}/\it D \rm ^{Cpx/SM}_{Sc}\end{array}$ together with literature data obtained at similar fo2 shows a nearly constant value of 1.68 ± 0.26, regardless of temperature, pressure, melt composition, and melt water content, indicating that these factors cannot cause fractionation of Sc3+ from mixed V3+ and V4+ in mantle melts through clinopyroxene/silicate melt partitioning. Therefore, in combination with V/Sc systematics in primitive MORBs and arc basalts, using DVCpx/SMandDScCpx/SM$\begin{array}{}D \rm ^{Cpx/SM}_{V}\,and\,\it D \rm ^{Cpx/SM}_{Sc}\end{array}$ obtained at 1 bar and dry conditions should be valid to constrain mantle fo2 except for the case that the DCpx/SM for Sc3+ can be demonstrated to be fractionated from the DCpx/SM for mixed V4+ and V5+, which are present in oxidized basalts. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png American Mineralogist de Gruyter

Temperature and pressure effects on the partitioning of V and Sc between clinopyroxene and silicate melt: Implications for mantle oxygen fugacity

American Mineralogist , Volume 103 (5): 5 – May 25, 2018

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Publisher
de Gruyter
Copyright
© 2018 Walter de Gruyter GmbH, Berlin/Boston
ISSN
0003-004X
eISSN
1945-3027
D.O.I.
10.2138/am-2018-6464
Publisher site
See Article on Publisher Site

Abstract

AbstractThe partition coefficients of V and Sc between clinopyroxene and silicate melt (DVCpx/SMandDScCpx/SM)$\begin{array}{}(D \rm ^{Cpx/SM}_{V}\,and\,\it D \rm ^{Cpx/SM}_{Sc})\end{array}$ have been determined experimentally at 1200–1400 °C and 0.8–2.3 GPa, using a hornblende- and clinopyroxene-rich mantle rock in graphite-lined Pt95Rh05 capsules. The results show that the DVCpx/SM$\begin{array}{}D \rm ^{Cpx/SM}_{V}\end{array}$ and DScCpx/SM$\begin{array}{}D \rm ^{Cpx/SM}_{Sc}\end{array}$ values decrease from 3.8 to 2.3 and from 2.6 to 1.1, respectively, as the experimental temperature and pressure vary from 1200 °C and 0.8 GPa to 1400 °C and 2.3 GPa. The presence of water in silicate melts may also reduce DVCpx/SMandDScCpx/SM.$\begin{array}{}D \rm ^{Cpx/SM}_{V} and \,\it{D} \rm ^{Cpx/SM}_{Sc}.\end{array}$ These results imply that the effects of temperature, pressure, and melt water content on DVCpx/SM$\begin{array}{}D \rm ^{Cpx/SM}_{V}\end{array}$ should be considered when using V systematics in cratonic mantle peridotites to constrain cratonic mantle oxygen fugacity (fo2). However, although the dominant V in the present silicate melt is mixed V3+ and V4+, the DVCpx/SM/DScCpx/SM$\begin{array}{}D \rm ^{Cpx/SM}_{V}/\it D \rm ^{Cpx/SM}_{Sc}\end{array}$ together with literature data obtained at similar fo2 shows a nearly constant value of 1.68 ± 0.26, regardless of temperature, pressure, melt composition, and melt water content, indicating that these factors cannot cause fractionation of Sc3+ from mixed V3+ and V4+ in mantle melts through clinopyroxene/silicate melt partitioning. Therefore, in combination with V/Sc systematics in primitive MORBs and arc basalts, using DVCpx/SMandDScCpx/SM$\begin{array}{}D \rm ^{Cpx/SM}_{V}\,and\,\it D \rm ^{Cpx/SM}_{Sc}\end{array}$ obtained at 1 bar and dry conditions should be valid to constrain mantle fo2 except for the case that the DCpx/SM for Sc3+ can be demonstrated to be fractionated from the DCpx/SM for mixed V4+ and V5+, which are present in oxidized basalts.

Journal

American Mineralogistde Gruyter

Published: May 25, 2018

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