Micro‐Raman study of crichtonite group minerals enclosed into mantle garnet. (15th September 2020)

• Record Type: Journal Article
• Authors: Alifirova, Taisia; Rezvukhin, Dmitriy; Nikolenko, Evgeny; Pokhilenko, Lyudmila; Zelenovskiy, Pavel; Sharygin, Igor; Korsakov, Andrey; Shur, Vladimir
• Other Names: Bersani Danilo guestEditor.; Barone Germana guestEditor.; Marshall Craig Patrick guestEditor.
• Is Part Of: Journal of Raman spectroscopy. Volume 51:Number 9(2020)
• Page Start: 1493
• Page End: 1512
• Publication Date: 2020-09-15
• Subjects: crichtonite group minerals -- mantle xenoliths -- oriented inclusions -- pyrope -- Raman spectroscopy; Raman spectroscopy -- Periodicals; 535.846
• DOI: 10.1002/jrs.5979
• Languages: English
• ISSNs: 0377-0486

Abstract

Abstract: We report the first comprehensive micro‐Raman study of crichtonite group minerals (CGM) as inclusions in pyropic garnet grains from peridotite and pyroxenite mantle xenoliths of the Yakutian kimberlites as well as in garnet xenocrysts from the Aldan shield lamprophyres (Russia). The CGM form (i) morphologically oriented needles, lamellae, and short prisms and (ii) optically unoriented subhedral to euhedral grains, either single or intergrown with other minerals. We considered common mantle‐derived CGM species (like loveringite, lindsleyite, and their analogues), with Ca, Ba, or Sr dominating in the dodecahedral A site and Zr or Fe in the octahedral B site. The Raman bands at the region of 600–830 cm −1 are indicative of CGM and their crystal‐chemical distinction, although the intensity and shape of the bands appear to be dependent on laser beam power and wavelength. The factor‐group analysis based on the loveringite crystal structure showed the octahedral and tetrahedral cation groups with 18 f and 6 c Wyckoff positions, namely, dominantly TiO6 and to a lower extent CrO6, MgO4, and FeO4 groups, to be the major contributors to the Raman spectral features. The ionic groups with dodecahedral (M0) and octahedral (M1) coordination are inactive for Raman scattering while active in infrared absorption. A number of observed Raman modes in the CGM spectra are several times lower than that predicted by the factor group analysis. The noticed broadening of modes in the CGM Raman spectra may result from a combining of bands at the narrow frequency shift regions. Solid solution behavior, luminescence, and partial metamictization of the CGM may exert additional influence on the Raman band shape. The Raman spectral features showed CGM to be accurately identified and distinguished from other Ti‐, Fe‐, Cr‐, and Zr‐containing oxides (e.g., ilmenite or those of spinel and magnetoplumbite groups) occurring as accessory mantle minerals. Abstract : Using the micro‐Raman spectroscopy, we have studied crichtonite group minerals (CGM; oxides with large‐ and medium‐sized cations) as inclusions in mantle garnet from a number of Siberian kimberlites and lamprophyres. The prominent Raman modes of the CGM occur within a region of 100–850 cm −1 . The Raman spectral features showed CGM to be accurately identified in samples and distinguished from other Ti‐, Fe‐, Cr‐, and Zr‐containing oxides (e.g., ilmenite, or those of spinel and magnetoplumbite groups) occurring as accessory mantle minerals.