Pyroxene europium valence oxybarometer: Effects of pyroxene composition, melt composition, and crystallization kinetics
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C.K. Shearer
,
J.J. Papike
Abstract
The behavior of multivalent elements such as Fe, Cr, V, and Eu in magmatic systems reflects the fO₂ of the environment. In particular, Eu behavior in pyroxene from basaltic systems has been demonstrated to be an effective measure of fO₂. We selected two nearly isochemical lunar pigeonite basalts (15058, 15499), a lunar high-Ti basalt (75035), and Pasamonte (representing asteroid 4 Vesta, an unequilibrated eucrite), to explore other potential variables that may affect this indicator of fO₂. All of these basalts crystallized at an fO₂ of approximately IW-1, yet they experienced different cooling and crystallization histories and their pyroxenes exhibit a wide range of compositional trajectories within the pyroxene quadrilateral. There are several variables that influence the Eu/Eu* recorded in pyroxene that may compromise the determination of fO₂. Previous experimental studies show that pyroxene composition influences the ability of pyroxene to accommodate REE and fractionate Eu2+ from Eu3+. We demonstrate that in addition to the influence of Ca in the M2 site, the Al content in the pyroxene and its influence on coupled substitutions will also influence the fractionation of Eu2+ from Eu3+. For example, the coupled substitution TSi4+ + M2R2+ → TAl3+ + M2REE3+ may accommodate REE3+ in preference to Eu2+, which is too large. Different pyroxene growth surfaces will incorporate Eu2+ and Eu3+ differently due to differences in growth rate, Al content, and site configuration. In consort with the pyroxene composition, fractionation of Eu2+ from Eu3+ will be aided by the Al content of the basaltic melt, which increases the activities of network-forming components such as CaAl2O4 and FeAl2O4 in the melt during pyroxene crystallization. The Al content will result in changing the partitioning behavior of Eu3+ while having very little effect on Eu2+. Melt composition, the appearance of plagioclase on the liquidus, and the kinetics of plagioclase crystallization are influenced by cooling rate. Data from the four basalts selected also suggest that Eu2+/Eu3+ in the melt remains buffered even with extreme differences in cooling rate and plagioclase crystallization kinetics. Unexpectedly, many of these same variables affect the substitution of multivalent V. If the fO₂ determined from Eu behavior in pyroxene is not placed within a petrologic and crystal-chemical context, errors of 1 to 2 log units may result. The influence of these variables may be reduced by using multiple, co-crystallizing phases (i.e., plagioclase and pyroxene) and ratioing DEu to adjacent REE (DSm, Gd).
© 2015 by Walter de Gruyter Berlin/Boston
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- Lithium isotopic systematics of granites and pegmatites from the Black Hills, South Dakota
- Identifying the effects of petrologic processes in a closed basaltic system using trace- element concentrations in olivines and glasses: Implications for comparative planetology
- Tectonic implications of diverse igneous blocks in Franciscan mélange, Northern California and southwestern Oregon
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- Experimental insights on crystal chemistry of high-Ti garnets from garnet-melt partitioning of rare-earth and high-field-strength elements
- The atomic arrangement of merrillite from the Fra Mauro Formation, Apollo 14 lunar mission: The first structure of merrillite from the Moon
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- Comparative planetary mineralogy: Pyroxene major- and minor-element chemistry and partitioning of vanadium between pyroxene and melt in planetary basalts
- Crystal chemistry of lunar merrillite and comparison to other meteoritic and planetary suites of whitlockite and merrillite
- An experimental study of trace-element partitioning between Ti-Al-clinopyroxene and melt: Equilibrium and kinetic effects including sector zoning
- Minor- and trace-element sector zoning in synthetic enstatite
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- Transformations of Mg- and Ca-sulfate hydrates in Mars regolith
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Articles in the same Issue
- Orbicular oxides in carbonatitic kimberlites
- Fluid-mediated polymetamorphism related to Proterozoic collision of Archean Wyoming and Superior provinces in the Black Hills, South Dakota
- Lithium isotopic systematics of granites and pegmatites from the Black Hills, South Dakota
- Identifying the effects of petrologic processes in a closed basaltic system using trace- element concentrations in olivines and glasses: Implications for comparative planetology
- Tectonic implications of diverse igneous blocks in Franciscan mélange, Northern California and southwestern Oregon
- The petrogenesis of the Apollo 14 high-Al mare basalts
- Experimental insights on crystal chemistry of high-Ti garnets from garnet-melt partitioning of rare-earth and high-field-strength elements
- The atomic arrangement of merrillite from the Fra Mauro Formation, Apollo 14 lunar mission: The first structure of merrillite from the Moon
- The behavior of Li and B in lunar mare basalts during crystallization, shock, and thermal metamorphism: Implications for volatile element contents of martian basalts
- Pyroxene europium valence oxybarometer: Effects of pyroxene composition, melt composition, and crystallization kinetics
- Comparative planetary mineralogy: Pyroxene major- and minor-element chemistry and partitioning of vanadium between pyroxene and melt in planetary basalts
- Crystal chemistry of lunar merrillite and comparison to other meteoritic and planetary suites of whitlockite and merrillite
- An experimental study of trace-element partitioning between Ti-Al-clinopyroxene and melt: Equilibrium and kinetic effects including sector zoning
- Minor- and trace-element sector zoning in synthetic enstatite
- Insights into the redox history of the NWA 1068/1110 martian basalt from mineral equilibria and vanadium oxybarometry
- Transformations of Mg- and Ca-sulfate hydrates in Mars regolith
- An experimental study of the oxidation state of vanadium in spinel and basaltic melt with implications for the origin of planetary basalt
- Valence state partitioning of vanadium between olivine-liquid: Estimates of the oxygen fugacity of Y980459 and application to other olivine-phyric martian basalts
- Identification of relict forsterite grains in forsterite-rich chondrules from the Mokoia CV3 carbonaceous chondrite
- Formation of spinel-, hibonite-rich inclusions found in CM2 carbonaceous chondrites
- Deep metastable eutectic condensation in Al-Fe-SiO-H2-O2 vapors: Implications for natural Fe-aluminosilicates
- α-PbO2-type nanophase of TiO2 from coesite-bearing eclogite in the Dabie Mountains, China–Comment
- α-PbO2-type nanophase of TiO2 from coesite-bearing eclogite in the Dabie Mountains, China–Reply
- Rietveld structure refinement of perovskite and post-perovskite phases of NaMgF3 (Neighborite) at high pressures
- Letter. Si vacancies in the 10-Å phase
