skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Quantifying and correcting the effects of anisotropy in XANES measurements of chromium valence in olivine: Implications for a new olivine oxybarometer

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
National Science Foundation (NSF)
OSTI Identifier:
1368291
Resource Type:
Journal Article
Resource Relation:
Journal Name: American Mineralogist; Journal Volume: 102; Journal Issue: 6
Country of Publication:
United States
Language:
ENGLISH

Citation Formats

Bell, Aaron S., Shearer, Charles, Burger, Paul, Ren, Minghua, Newville, Matthew, and Lanzirotti, Antonio. Quantifying and correcting the effects of anisotropy in XANES measurements of chromium valence in olivine: Implications for a new olivine oxybarometer. United States: N. p., 2017. Web. doi:10.2138/am-2017-5911.
Bell, Aaron S., Shearer, Charles, Burger, Paul, Ren, Minghua, Newville, Matthew, & Lanzirotti, Antonio. Quantifying and correcting the effects of anisotropy in XANES measurements of chromium valence in olivine: Implications for a new olivine oxybarometer. United States. doi:10.2138/am-2017-5911.
Bell, Aaron S., Shearer, Charles, Burger, Paul, Ren, Minghua, Newville, Matthew, and Lanzirotti, Antonio. Thu . "Quantifying and correcting the effects of anisotropy in XANES measurements of chromium valence in olivine: Implications for a new olivine oxybarometer". United States. doi:10.2138/am-2017-5911.
@article{osti_1368291,
title = {Quantifying and correcting the effects of anisotropy in XANES measurements of chromium valence in olivine: Implications for a new olivine oxybarometer},
author = {Bell, Aaron S. and Shearer, Charles and Burger, Paul and Ren, Minghua and Newville, Matthew and Lanzirotti, Antonio},
abstractNote = {},
doi = {10.2138/am-2017-5911},
journal = {American Mineralogist},
number = 6,
volume = 102,
place = {United States},
year = {Thu Jun 01 00:00:00 EDT 2017},
month = {Thu Jun 01 00:00:00 EDT 2017}
}
  • The oxidation state of Cr in 200 [mu]m regions within individual lunar olivine and pyroxene grains from lunar basalt 15555 was inferred using X-ray Absorption Near Edge Structure (XANES). Reference materials had previously been studied by optical absorption spectroscopy and included Cr-bearing borosilicate glasses synthesized under controlled oxygen fugacity and Cr-doped olivines. The energy dependence of XANES spectral features defined by these reference materials indicated that Cr is predominantly divalent in the lunar olivine and trivalent in the pyroxene. These results coupled with the apparent f[sub o[sub 2]]-independence of partitioning coefficients for Cr into olivine imply that the source magmamore » was dominated by divalent Cr at the time of olivine crystallization. 29 refs., 8 figs., 1 tab.« less
  • Experiments on a Martian basalt composition show that D{sub V} augite/melt is greater than D{sub V} pigeonite/melt in samples equilibrated under the same fO{sub 2} conditions. This increase is due to the increased availability of elements for coupled substitution with the V{sup 3+} or V{sup 4+} ions, namely Al and Na. for this bulk composition, both Al and Na are higher in concentration in augite compared with pigeonite; therefore more V can enter augite than pigeonite. Direct valence state determination by XANES shows that the V{sup 3+} and V{sup 4+} are the main V species in the melt at fO{submore » 2} conditions of IW-1 to IW+3.5, whereas pyroxene grains at IW-1, IW, and IW+1 contain mostly V{sup 3+}. This confirms the idea that V{sup 3+} is more compatible in pyroxene than V{sup 4+}. The Xanes data also indicates that a small percentage of V{sup 2+} may exist in melt and pyroxene at IW-1. The similar valence of V in glass and pyroxene at IW-1 suggests that V{sup 2+} and V{sup 3+} may have similar compatibilities in pyroxene.« less
  • The relative proportion of divalent and trivalent Eu has proven to be a useful tool for estimating f{sub O{sub 2}} in various magmatic systems. However, in most cases, direct determination of the Eu valence state has not been made. In this study, direct determination of Eu valence by XANES and REE abundance in merrillite provide insights into the crystal chemistry of these phosphates and their ability to record conditions of magmatism. Merrillite strongly prefers Eu{sup 3+} to Eu{sup 2+}, with the average valence state of Eu ranging between 2.9 and 3 over approximately six orders of magnitude in f{sub O{submore » 2}}. The dramatic shift in the REE patterns of merrillite in martian basaltic magmas, from highly LREE-depleted to LREE-enriched, parallels many other trace element and isotopic variations and reflects the sources for these magmas. The behavior of REE in the merrillite directly reflects the relationship between the eightfold-coordinated Ca1 site and adjacent sixfold Na and tetrahedral P sites that enables charge balancing through coupled substitutions.« less
  • Vanadium can exist in a large number of valence states in nature (2+?, 3+, 4+ and 5+) and determinations of V valence is therefore valuable in defining the oxidation states of earth and planetary materials over a large redox range. Synchrotron-based x-ray absorption near edge structure (XANES) spectroscopy is well-suited for measurements of V valence with {approx}micrometer spatial resolution and {approx}ppm elemental sensitivity. Applications of microXANES have been demonstrated for basaltic glasses. Applications to minerals are feasible but complicated by orientation effects (e.g. due to polarization of the synchrotron x-ray beam) and some results for spinel have been reported. Heremore » we report initial results for olivine from laboratory crystallization ex-periments. The goal is to define the valence partition-ing between olivine and melt and quantify the magnitude of orientation effects, the latter tested by measuring grains at a variety of orientations in the same charge.« less