• journal_title：American Mineralogist
• Contributor：Steeve Gréaux ; François Farges ; Laurent Gautron ; Nicolas Trcera ; Anne-Marie Flank ; Pierre Lagarde
• Publisher：Mineralogical Society of America
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2012.3811
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：97
• issue：1
• firstpage：100
• section：Articles

X-ray absorption spectroscopy was used to investigate the oxidation state of uranium in various U- and Th-bearing Al-rich CaSiO₃ perovskite samples synthesized at high-pressure and high-temperature using a multi-anvil press apparatus. X-ray absorption near edge spectroscopy (XANES) spectra collected at the U L_III- and Th L_III-edges using both micro- and macro-focused beams show U⁴⁺ in the Al-rich CaSiO₃ perovskite. The structure of the U- and Th-bearing Al-rich CaSiO₃ perovskite samples have been cross-checked by XANES spectra collected at the Ca K-, Al K-, and Si K-edges. Al K and Si K spectra suggest that Al incorporates exclusively on the Si site of the CaSiO₃ perovskite. Ca K spectra of the (U,Th)-bearing Al-rich CaSiO₃ perovskite samples were succesfully compared to FEFF8.2 ab initio models of a tetragonal CaSiO₃ perovskite with space group P4/mmm.

Our results confirm previous assumptions of the coupled substitution of CaSi₂ by UAl₂ in CaSiO₃ perovskite and that U and Th can be incorporated separately or together in CaSiO₃ perovskite by means of this mechanism. The possible occurrence of the U- and Th-bearing Al-rich CaSiO₃ perovskite are discussed as a potential candidate to locally host a large amount of actinides in the Earth’s deep mantle. The study of a phase that can act as a storage mineral for heat-producing actinide elements such as uranium and thorium is fundamental to the understanding of the geodynamics and thermal behavior of Earth.