Micro‐Raman study of crichtonite group minerals enclosed into mantle garnet

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 18f and 6c 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.

Cr-pyrope xenocrysts with oxide mineral inclusions from the Chompolo lamprophyres (Aldan shield): Insights into mantle processes beneath the southeastern Siberian craton

“…The abundance of such minerals as water-bearing silicates, carbonates, sulfides, graphite and apatite in Chompolo pyropes (more than 15 minerals; Nikolenko et al, 2017Nikolenko et al, , 2021Sharygin et al, 2017;Alifirova et al, 2020;this study) indicates that the fluid/melt also contained significant volatile components (H 2 O, CO 2, S, P, Cl). The monomineral and polymineral inclusions studied here are similar to the associations found in pyropes from ultramafic diatremes of the Navajo volcanic field, Colorado plateau (McGetchin and Silver, 1970;Hunter and Smith, 1981;Smith, 1987Smith, , 2020Wang et al, 1999).…”

“…A significant controversy surrounds the issue of Ti-oxide needle origin in Сr-pyrope since the criteria to distinguish epigenetic inclusions from syngenetic ones are not obvious. As a rule, elongated oxide inclusions in Cr-pyrope are oriented along specific crystallographic directions (Alifirova et al, 2012(Alifirova et al, , 2020Wang et al, 1999;Vrana, 2008;Rezvukhin et al, 2018Rezvukhin et al, , 2019.…”

“…Available mineralogical data indicate the Cr-pyrope of the lherzolitic paragenesis as being the principal host for a series of Ti-rich oxide inclusions namley: rutile, Mg-rich ilmenite (‘picroilmenite’), crichtonite-group minerals, srilankite and carmichaelite (Botkunov et al , 1987, Kostrovitsky and Garanin, 1992, Wang et al , 1999; Săbău and Alberico, 2003; Vrana, 2008; Alifirova et al , 2012, 2020; Ziberna et al , 2013; Nikolenko et al , 2017, 2021; Rezvukhin et al , 2018, 2019). Although there is characteristic enrichment in Ti and Fe, these oxide phases also contain elevated amounts of silicate-incompatible elements, such as high-field-strength elements (HFSE: Nb, Zr and Ta) in rutile, Zr in srilankite, and an exotic array of large ion lithophile elements (LILE: Ba, Sr and K), HFSE, and light rare earth elements (LREE: La, Ce) in the crichtonite-group minerals.…”

“…The subcontinental lithospheric mantle beneath the Aldan shield remains one of the least studied mantle sections within the Siberian craton, because xenogenic material of deeply-sourced rocks has been given a much lower priority compared to the host rocks. Apart from a few reports dealing with mantle-derived garnet and clinopyroxene xenocrysts from the Chompolo and Tobuk–Khatystyr fields (Kostrovitsky and Garanin, 1992; Varlamov et al , 1996; Ashchepkov et al , 2001; Nikolenko et al , 2017, 2021; Alifirova et al , 2020) and a series of investigations devoted to the xenoliths occurring in alkali basalts from Tok, Stanovoy terrane, southern Aldan shield (Ionov et al , 2005; Tommasi et al , 2008 and references therein), little is known of the composition, structure and thermal state of the lithospheric mantle beneath the Aldan shield. Located in the Central Aldan, lamprophyres of the Chompolo field are a valuable source of information concerning mantle parageneses as they contain abundant Cr-pyrope xenocrysts with associated mineral inclusions of remarkable diversity: Ti–Cr-rich oxides, silicates, carbonates, sulfides, hydrous minerals, graphite and composite polymineralic inclusions (Kostrovitsky and Garanin, 1992; Nikolenko et al , 2017, 2021; Alifirova et al , 2020; this study).…”

40Ar/39Ar Geochronology and New Mineralogical and Geochemical Data from Lamprophyres of Chompolo Field (South Yakutia, Russia)

“…Mineral assemblages in the pyropes from the Central Aldan subcontinental lithospheric mantle (SCLM) were described previously in separate studies [103,114,145,146]. The composition of mineral inclusions in lherzolitic and harzburgitic Cr-pyropes from the Aldanskya dyke and Ogonek pipe is evidence of metasomatic mineral associations in the mantle under the Aldan shield.…”