MgAl2O4 spinels from Allende and NWA 763 carbonaceous chondrites: Structural refinement, cooling history, and trace element contents

1Davide Lenaz,2Vanni Lughi,3Diego Perugini,3,4Maurizio Petrelli,5Gianluca Turco,6Birger Schmitz
Meteoritics & Planetary Science (in Press) Link to Article []
1Department of Mathematics and Geosciences, University of Trieste, 34128 Trieste, Italy
2Department of Engineering and Architecture, University of Trieste, 34127 Trieste, Italy
3Department of Physics and Geology, University of Perugia,06123 Perugia, ltaly
4INFN, Sezione di Perugia, 06123 Perugia, Italy
5Department of Medical Sciences, University of Trieste,Piazza dell’Ospitale 1, 34125 Trieste, Italy
6Astrogeobiology Laboratory, Department of Physics, Lund University, 22100 Lund, Sweden
Published by arrangement with John Wiley & Sons

MgAl2O4 spinels from Allende and NWA 763 carbonaceous chondrites were studied by X‐ray single crystal diffraction, SEM, electron microprobe, LA‐ICP‐MS, and Raman spectroscopy. Those from Allende are almost pure, but, in one case, we found a strong FeOtot zonation. Spinels from NWA 763 show Mg‐Fe2+ substitutions. Almost pure MgAl2O4 spinels from both meteorites underwent slow cooling and reached their intracrystalline closure temperature (Tc) in the range 460–520 °C. The NWA 763 spinel with higher FeO content shows a Tc of about 720 °C. X‐ray single crystal diffraction and Raman spectroscopy suggest a slow cooling and an ordered structure with trivalent cations in M site and divalent in T site. Among the trace elements, Ti and Co are enriched with respect to the terrestrial analogs, while Mn, Ni, and Sn show intermediate values between different terrestrial occurrences. Vanadium cannot be used as a tracer of extraterrestrial origin as for Cr‐spinels, because its content is similar in extraterrestrial and terrestrial spinels. In the zoned crystal from Allende, Co show a strong zonation similar to that of FeO.


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