TY - JOUR

T1 - Confocal Raman spectroscopic study of melt inclusions in olivine of mantle xenoliths from the Bultfontein kimberlite pipe (Kimberley cluster, South Africa): Evidence for alkali-rich carbonate melt in the mantle beneath Kaapvaal Craton

AU - Sharygin, Igor S.

AU - Golovin, Alexander V.

AU - Tarasov, Alexey A.

AU - Dymshits, Anna M.

AU - Kovaleva, Elizaveta

N1 - Funding Information: This work was supported by the Russian Foundation for Basic Research (grant No. 20‐35‐70058) and by the Ministry of Science and Higher Education of the Russian Federation by the state assignment projects of IEC SB RAS and IGM SB RAS. Samples used in this study were collected during a field trip to the Kimberley area in 2017 that were supported by the Russian Foundation for Basic Research (grant No. 16‐35‐60052). The authors are thankful to J. Robey for help with sample collecting. Publisher Copyright: © 2021 John Wiley & Sons, Ltd.

PY - 2022/3

Y1 - 2022/3

N2 - Identifying the composition of primary/primitive mantle melts is crucial for understanding the mantle's evolution and mantle-derived magmatism. Melt inclusions in mantle xenoliths provide key information about such melts. This study used confocal Raman spectroscopy to characterize mineral assemblage of unexposed crystallized secondary melt inclusions in the olivine from the xenoliths of the sheared garnet peridotites from the Bultfontein kimberlite pipe (Kimberley cluster, Kaapvaal Craton, South Africa). The studied peridotites originated from 112- to 146-km mantle depths. In total, 16 minerals were identified among daughter crysatls, which include carbonates (calcite, magnesite, dolomite), alkali carbonates (eitelite, nyerereite, gregoryite/natrite, K–Na–Ca–carbonate (K,Na)2Ca(CO3)2 (K analogue of nyerereite), alkali carbonates with additional anions (northupite, bradleyite, burkeite), alkali sulfates (glauberite, thenardite, aphthitalite), apatite, tetraferriphlogopite, and magnetite. Several more daughter minerals gave distinct Raman spectra, but they were not determined due to the lack of similar spectra in the databases. Carbonates are predominant among the daughter minerals in the melt inclusions. Many daughter minerals are rich in alkalis. These facts indicate that melt(s), parental for the inclusions, is alkali-rich carbonate in composition. Two possible models were suggested for the origin of these melt inclusions: (1) in situ fracturing of olivine and the mantle melt infiltration shortly before the sheared peridotites were entrained by the ascending kimberlitic magma; (2) infiltration of the transporting kimberlite melt into xenoliths during ascent. Both models imply that the alkali-rich carbonate melt(s) that interacted with peridotites originated at a greater depth than the entrapment level of studied xenoliths (>150 km), that is, at the base of the lithosphere or in the asthenosphere. This melt is genetically related to the kimberlite magmatism that formed the Bultfontein pipe and points at the alkali-rich carbonate composition of primary kimberlite melt.

AB - Identifying the composition of primary/primitive mantle melts is crucial for understanding the mantle's evolution and mantle-derived magmatism. Melt inclusions in mantle xenoliths provide key information about such melts. This study used confocal Raman spectroscopy to characterize mineral assemblage of unexposed crystallized secondary melt inclusions in the olivine from the xenoliths of the sheared garnet peridotites from the Bultfontein kimberlite pipe (Kimberley cluster, Kaapvaal Craton, South Africa). The studied peridotites originated from 112- to 146-km mantle depths. In total, 16 minerals were identified among daughter crysatls, which include carbonates (calcite, magnesite, dolomite), alkali carbonates (eitelite, nyerereite, gregoryite/natrite, K–Na–Ca–carbonate (K,Na)2Ca(CO3)2 (K analogue of nyerereite), alkali carbonates with additional anions (northupite, bradleyite, burkeite), alkali sulfates (glauberite, thenardite, aphthitalite), apatite, tetraferriphlogopite, and magnetite. Several more daughter minerals gave distinct Raman spectra, but they were not determined due to the lack of similar spectra in the databases. Carbonates are predominant among the daughter minerals in the melt inclusions. Many daughter minerals are rich in alkalis. These facts indicate that melt(s), parental for the inclusions, is alkali-rich carbonate in composition. Two possible models were suggested for the origin of these melt inclusions: (1) in situ fracturing of olivine and the mantle melt infiltration shortly before the sheared peridotites were entrained by the ascending kimberlitic magma; (2) infiltration of the transporting kimberlite melt into xenoliths during ascent. Both models imply that the alkali-rich carbonate melt(s) that interacted with peridotites originated at a greater depth than the entrapment level of studied xenoliths (>150 km), that is, at the base of the lithosphere or in the asthenosphere. This melt is genetically related to the kimberlite magmatism that formed the Bultfontein pipe and points at the alkali-rich carbonate composition of primary kimberlite melt.

KW - carbonate

KW - carbonate melt

KW - craton

KW - kimberlite

KW - mantle xenoliths

UR - http://www.scopus.com/inward/record.url?scp=85109950267&partnerID=8YFLogxK

U2 - 10.1002/jrs.6198

DO - 10.1002/jrs.6198

M3 - Article

AN - SCOPUS:85109950267

VL - 53

SP - 508

EP - 524

JO - Journal of Raman Spectroscopy

JF - Journal of Raman Spectroscopy

SN - 0377-0486

IS - 3

ER -