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Title: Direct determination of europium valence state by XANES in extraterrestrial merrillite: Implications for REE crystal chemistry and martian magmatism

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{sub 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.
Authors:
; ; ; ; ;  [1] ;  [2]
  1. (UNM)
  2. (
Publication Date:
OSTI Identifier:
1034195
Resource Type:
Journal Article
Resource Relation:
Journal Name: Am. Mineral.; Journal Volume: 96; Journal Issue: (8-9) ; 08, 2011
Research Org:
Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
Sponsoring Org:
NSFDOE - BASIC ENERGY SCIENCESNASA
Country of Publication:
United States
Language:
ENGLISH
Subject:
58 GEOSCIENCES; ABUNDANCE; CHEMISTRY; ELEMENTS; EUROPIUM; MAGMATISM; PHOSPHATES; TRACE AMOUNTS; VALENCE