Formation of spongy clinopyroxene: insights from eclogitic inclusions in diamonds

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dc.contributor.authorWang, Wenyuen
dc.contributor.authorKorolev, Nester M.en
dc.contributor.authorKiseeva, Ekaterina S.en
dc.contributor.authorDavies, Rondi M.en
dc.contributor.authorWeiss, Yaakoven
dc.contributor.authorKopylova, Mayaen
dc.contributor.authorTowbin, W. Henryen
dc.contributor.authorHuang, Fangen
dc.contributor.authorMoore, Andy E.en
dc.contributor.authorVasilev, Evgeniy A.en
dc.contributor.funderIrish Research Councilen
dc.contributor.funderRichard Gilder Graduate Schoolen
dc.contributor.funderAmerican Museum of Natural Historyen
dc.contributor.funderNational Science Foundationen
dc.contributor.funderRussian Science Foundationen
dc.date.accessioned2025-05-30T09:05:30Z
dc.date.available2025-05-30T09:05:30Z
dc.date.issued2025-05-01en
dc.description.abstractSpongy clinopyroxene is common in most mantle-derived xenoliths and megacrysts of eclogitic and peridotitic parageneses. Its formation is commonly attributed to the partial melting of a primary clinopyroxene in response to various factors, including changes in pressure and temperature or infiltration of external melts or fluids. In order to study the mechanism of spongy clinopyroxene formation in detail, we selected six eclogitic clinopyroxene inclusions in diamonds with varying amounts of spongy clinopyroxene (from ~10 to 100%). We employed computed tomography, electron microprobe analysis, and Raman spectroscopy to study the textural characteristics, major element concentrations, and the types of volatiles present in both phases. We also used pMELTS to model the compositions of spongy clinopyroxene and associated melts produced by the melting of primary clinopyroxene over a range of pressures and temperatures. We compare these results with estimates from major element thermobarometry of the spongy clinopyroxene. We conclude that the studied spongy clinopyroxene is the solid product of partial melting that occurs upon decompression of the primary clinopyroxene within the diamond in a near-closed system. Melting of the primary clinopyroxene occurred continuously or in pulses at different depths during the diamond’s ascent to Earth’s surface and produced variable spongy clinopyroxene and melt compositions even within the same inclusion. This is possible due to relatively rapid kimberlite ascent. The degrees of melting are various and unexpectedly high for mantle melting (between <10 and 60% with an average of ~20–30%). The produced melts are highly silicic, phonolitic, and alkali-rich. pMELTS modelling shows the spongy clinopyroxene compositions can be reproduced at pressures between 0.5–2.7 GPa and temperatures of 850–1300°C, with the majority of them satisfying the P–T conditions of 1–2 GPa and 1100–1300°C. This indicates decompression melting of primary clinopyroxene at shallow upper mantle or lower crustal conditions.en
dc.description.sponsorshipIrish Research Council (IRCLA/2022/2638); Kalbfleisch Fellowship; Russian Science Foundation (21-77-20026); National Science Foundation (2320473)en
dc.description.statusPeer revieweden
dc.description.versionPublished Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.citationWang, W., Korolev, N. M., Kiseeva, E. S., Davies, R. M., Weiss, Y., Kopylova, M., Towbin, W. H., Huang, F., Moore, A. E. and Vasilev, E. A. (2025) 'Formation of spongy clinopyroxene: insights from eclogitic inclusions in diamonds', Journal of Petrology, 66(5), egaf036 (19pp). https://doi.org/10.1093/petrology/egaf036en
dc.identifier.doi10.1093/petrology/egaf036en
dc.identifier.eissn1460-2415en
dc.identifier.endpage19en
dc.identifier.issn0022-3530en
dc.identifier.issued5en
dc.identifier.journaltitleJournal of Petrologyen
dc.identifier.startpage1en
dc.identifier.urihttps://hdl.handle.net/10468/17587
dc.identifier.volume66en
dc.language.isoenen
dc.publisherOxford University Pressen
dc.relation.ispartofJournal of Petrologyen
dc.rights© 2025, the Authors. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.en
dc.rights.urihttps://creativecommons.org/licenses/by/4.0/en
dc.subjectDiamond inclusionsen
dc.subjectKimberlite ascenten
dc.subjectSpongy clinopyroxeneen
dc.subjectThermobarometryen
dc.titleFormation of spongy clinopyroxene: insights from eclogitic inclusions in diamondsen
dc.typeArticle (peer-reviewed)en
oaire.citation.issue5en
oaire.citation.volume66en
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