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Alkali-carbonate melts from the base of cratonic lithospheric mantle: links to kimberlites

Citation

Golovin, AV and Sharygin, IS and Kamenetsky, VS and Korsakov, AV and Yaxley, GM, Alkali-carbonate melts from the base of cratonic lithospheric mantle: links to kimberlites, Chemical Geology, 483 pp. 261-274. ISSN 0009-2541 (2018) [Refereed Article]

Copyright Statement

2018 Published by Elsevier B.V.

DOI: doi:10.1016/j.chemgeo.2018.02.016

Abstract

Identification of the primary compositions of mantle-derived melts is crucial for understanding mantle compositions and physical conditions of mantle melting. However, these melts rarely reach the Earth's surface unmodified because of contamination, crystal fractionation and degassing, processes that occur almost ubiquitously after melt generation. Here we report snapshots of the melts preserved in sheared peridotite xenoliths from the Udachnaya-East kimberlite pipe, in the central part of the Siberian craton. These xenoliths are among the deepest mantle samples and were delivered by kimberlite magma from 180230 km depth interval, i.e. from the base of the cratonic lithosphere. The olivine grains of the sheared peridotites contain secondary inclusions of the crystallized melt with bulk molar (Na + K)/Ca ~ 3.4. Various Na-K-Ca-, Na-Ca-, Na-Mg-, Ca-Mg- and Ca-carbonates, Na-Mg-carbonates with additional anions, alkali sulphates and halides are predominant among the daughter minerals in secondary melt inclusions, whereas silicates, oxides, sulphides and phosphates are subordinate. These inclusions can be considered as ClS-bearing alkali-carbonate melts. The presence of aragonite, a high-pressure polymorph of CaCO3, among the daughter minerals suggests a mantle origin for these melt inclusions. The secondary melt inclusions in olivine from the sheared peridotite xenoliths and the melt inclusions in phenocrystic olivines from the host kimberlites demonstrate similarities, in daughter minerals assemblages and trace-element compositions. Moreover, alkali-rich minerals (carbonates, halides, sulphates and sulphides) identified in the studied melt inclusions are also present in the groundmass of the host kimberlites. These data suggests a genetic link between melt enclosed in olivine from the sheared peridotites and melt parental to the Udachnaya-East kimberlites. We suggest that the melt inclusions in olivine from mantle xenoliths may represent near primary, kimberlite melts. These results are new evidence in support of the alkali‑carbonate composition of kimberlite melts in their source regions, prior to the kimberlite emplacement into the crust, and are in stark contrast to the generally accepted ultramafic silicate nature of parental kimberlite liquids.

Item Details

Item Type:Refereed Article
Keywords:mantle xenoliths, kimberlites, carbonatite melts, mantle metasomatism, melt inclusions, aragonite, alkaline minerals
Research Division:Earth Sciences
Research Group:Geology
Research Field:Igneous and Metamorphic Petrology
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
UTAS Author:Kamenetsky, VS (Professor Vadim Kamenetsky)
ID Code:125783
Year Published:2018
Funding Support:Australian Research Council (DP1092823)
Web of Science® Times Cited:18
Deposited By:CODES ARC
Deposited On:2018-05-05
Last Modified:2019-03-12
Downloads:0

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