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Was crustal contamination involved in the formation of the serpentine-free Udachnaya-East kimberlite? New insights into parental melts, liquidus assemblage and effects of alteration

Abersteiner, A, Kamenetsky, VS ORCID: 0000-0002-2734-8790, Golovin, AV, Kamenetsky, M ORCID: 0000-0002-0417-3975 and Goemann, K ORCID: 0000-0002-8136-3617 2018 , 'Was crustal contamination involved in the formation of the serpentine-free Udachnaya-East kimberlite? New insights into parental melts, liquidus assemblage and effects of alteration' , Journal of Petrology , pp. 1-71 , doi: 10.1093/petrology/egy068.

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Abstract

The petrologically unique Udachnaya-East kimberlite (Siberia, Russia) is characterised by unserpentinised and H2O-poor volcaniclastic and coherent units that contain fresh olivine, along with abundant alkali-rich carbonates, chlorides, sulphides and sulphates in the groundmass. These mineralogical and geochemical characteristics have led to two divergent models that advocate different origins. It has been suggested that the unserpentinised units from Udachnaya-East are representative of pristine unaltered kimberlite. Conversely, the alkali-chlorine-sulphur enrichment has been attributed to interactions with crustal materials and, or, post-emplacement contamination by brines. The mineralogical and geochemical features and the compositions of melt inclusions in unserpentinised and serpentinised Udachnaya-East kimberlite varieties are compared in this study. Both varieties of kimberlite have similar major, compatible and incompatible trace element concentrations and primitive mantle normalised trace element patterns, groundmass textures and silicate, oxide and sulphide mineral compositions. However, these two kimberlite varieties are distinguished by: (i) the presence of unaltered olivine, abundant Na-K-Cl-S-rich minerals (i.e. chlorides, Sbearing alkali-carbonates, sodalite) and the absence of H2O-rich phases (i.e. serpentine, iowaite (Mg4Fe3+(OH)8OCl•3(H2O)) in unserpentinised samples, and (ii) the absence of alkali- and chlorine-enriched phases in the groundmass and characteristic olivine alteration (i.e. replacement by serpentine and, or, iowaite) in serpentinised samples. In addition, melt inclusions hosted in olivine, monticellite, spinel and perovskite from unserpentinised and serpentinised kimberlite contain identical daughter phase assemblages that are dominated by alkali-carbonates, chlorides and sulphates/sulphides. This enrichment in alkalis, chlorine and sulphur in melt inclusions demonstrates that these elements were an intrinsic part of the parental magma. The paucity of alkali-carbonates and chlorides in the groundmass of serpentinised Udachnaya-East kimberlite is attributed to their instability and removal during post-emplacement alteration. All evidence previously used in support of crustal and brine contamination of the Udachnaya-East kimberlite is thoroughly evaluated. We demonstrate that “contamination models” are inconsistent with petrographic, geochemical and melt inclusion data. Our combined data suggest that the Udachnaya-East kimberlite crystallised from an essentially H2O-poor, Si-Na-K-Cl-S-bearing carbonate-rich melt.

Item Type: Article
Authors/Creators:Abersteiner, A and Kamenetsky, VS and Golovin, AV and Kamenetsky, M and Goemann, K
Keywords: kimberlites, melt inclusions, halogens, alkali carbonate, mantle
Journal or Publication Title: Journal of Petrology
Publisher: Oxford University Press
ISSN: 0022-3530
DOI / ID Number: 10.1093/petrology/egy068
Copyright Information:

© The Author(s) 2018. Published by Oxford University Press. All rights reserved.This is a pre-copyedited, author-produced version of an article accepted for publication in Journal of Petrology following peer review. The version of record Abersteiner, A., Kamenetsky, V. S., Golovin, A. V., Kamenetsky, M., Goemann, K., Was crustal contamination involved in the formation of the serpentine-free Udachnaya-East kimberlite? New insights into parental melts, liquidus assemblage and effects of alteration, Journal of petrology, 59, (8) Article egy068 is available online at: https://doi.org/10.1093/petrology/egy068

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