XANES study of the oxidation state of Cr in lower mantle phases: Periclase and magnesium silicate perovskite

被引:28
作者
Eeckhout, Sigrid Griet
Bolfan-Casanova, Nathalie
McCammon, Catherine
Klemme, Stephan
Amiguet, Elodie
机构
[1] European Synchrotron Radiat Facil, F-38043 Grenoble, France
[2] Univ Clermont Ferrand, F-63038 Clermont Ferrand, France
[3] Univ Bayreuth, Bayer Geoinst, D-95440 Bayreuth, Germany
[4] Univ Edinburgh, Sch Geosci, Edinburgh EH9 3JW, Midlothian, Scotland
[5] Univ Edinburgh, CSEC, Edinburgh EH9 3JW, Midlothian, Scotland
关键词
XANES; Cr oxidation state; ferropericlase; periclase; Cr : MgSiO3 perovskite;
D O I
10.2138/am.2007.2318
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Cr K-edge X-ray absorption near-edge structure (XANES) spectra were recorded on Cr:MgO periclase and Cr:(Mg,Fe)O ferropericlase synthesized at different pressures (4 and 12 GPa) and temperatures (1200 to 1400 degrees C) at reducing oxygen fugacity conditions (similar to iron-wustite buffer IW to IW -2), and on Cr:MgSiO3 perovskite with 0.5 wt% Cr2O3. Fe-57 Mossbauer spectra were collected on the Fe-containing samples. The aim of the study was to determine the Cr oxidation state in phases found in the Earth's lower mantle, and to examine the possible relationship with the Fe oxidation state in the same materials. To calculate the amount of Cr2+, the intensity of the shoulder at the low-energy side of the edge crest was quantified using the area of the corresponding peak in the derivative XANES spectra (Berry and O'Neill 2004). In Cr:(Mg,Fe)O the relative Cr2+ content reached at most 12.5% but results from Mossbauer spectroscopy combined with chemical composition data suggest that some Cr2+ oxidized during cooling through the reaction Cr2+ + Fe3+ -> Cr3+ + Fe2+. In iron-free Cr:MgO, the Cr2+ content is much higher and reaches similar to 40%. In Cr:MgSiO3 perovskite with 0.006 Cr pfu (similar to estimated lower mantle abundance), chromium is mainly divalent.
引用
收藏
页码:966 / 972
页数:7
相关论文
共 38 条
[1]   THE CHEMICAL-COMPOSITION OF THE EARTH [J].
ALLEGRE, CJ ;
POIRIER, JP ;
HUMLER, E ;
HOFMANN, AW .
EARTH AND PLANETARY SCIENCE LETTERS, 1995, 134 (3-4) :515-526
[2]   Cationic substitution in MgSiO3 perovskite [J].
Andrault, D .
PHYSICS OF THE EARTH AND PLANETARY INTERIORS, 2003, 136 (1-2) :67-78
[3]  
Berry AJ, 2004, AM MINERAL, V89, P790
[4]   A furnace design for XANES spectroscopy of silicate melts under controlled oxygen fugacities and temperatures to 1773 K [J].
Berry, AJ ;
Shelley, JMG ;
Foran, GJ ;
O'Neill, HS ;
Scott, DR .
JOURNAL OF SYNCHROTRON RADIATION, 2003, 10 :332-336
[5]   Water partitioning at 660 km depth and evidence for very low water solubility in magnesium silicate perovskite [J].
Bolfan-Casanova, N ;
Keppler, H ;
Rubie, DC .
GEOPHYSICAL RESEARCH LETTERS, 2003, 30 (17) :SDE3-1
[6]   Water partitioning between nominally anhydrous minerals in the MgO-SiO2-H2O system up to 24 GPa:: implications for the distribution of water in the Earth's mantle [J].
Bolfan-Casanova, N ;
Keppler, H ;
Rubie, DC .
EARTH AND PLANETARY SCIENCE LETTERS, 2000, 182 (3-4) :209-221
[7]  
Burns R.G., 1993, Mineralogical Applications of Crystal Field Theory, V5
[8]   COORDINATION OF IRON IN OXIDE GLASSES THROUGH HIGH-RESOLUTION K-EDGE SPECTRA - INFORMATION FROM THE PRE-EDGE [J].
CALAS, G ;
PETIAU, J .
SOLID STATE COMMUNICATIONS, 1983, 48 (07) :625-629
[9]  
Dobson DP, 1998, AM MINERAL, V83, P794
[10]   The electrical conductivity of the lower mantle phase magnesiowustite at high temperatures and pressures [J].
Dobson, DP ;
Brodholt, JP .
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 2000, 105 (B1) :531-538