Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature

Abstract Metamorphic diamonds hosted by major and accessory phases in ultrahigh-pressure (UHP) metamorphic terranes represent important indicators of deep subduction and exhumation of continental crust at convergent plate boundaries. However, their nucleation and growth mechanisms are not well under...

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Autores principales:	J. Kotková, Y. Fedortchouk, R. Wirth, M. J. Whitehouse
Formato:	article
Lenguaje:	EN
Publicado:	Nature Portfolio 2021
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/f6d5b5892a714f4e89311eb149504134
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spelling	oai:doaj.org-article:f6d5b5892a714f4e89311eb1495041342021-12-02T18:15:33ZMetamorphic microdiamond formation is controlled by water activity, phase transitions and temperature10.1038/s41598-021-87272-12045-2322https://doaj.org/article/f6d5b5892a714f4e89311eb1495041342021-04-01T00:00:00Zhttps://doi.org/10.1038/s41598-021-87272-1https://doaj.org/toc/2045-2322Abstract Metamorphic diamonds hosted by major and accessory phases in ultrahigh-pressure (UHP) metamorphic terranes represent important indicators of deep subduction and exhumation of continental crust at convergent plate boundaries. However, their nucleation and growth mechanisms are not well understood due to their small size and diversity. The Bohemian microdiamond samples represent a unique occurrence of monocrystalline octahedral and polycrystalline cubo-octahedral microdiamonds in two different metasedimentary rock types. By combining new and published data on microdiamonds (morphology, resorption, associated phases, carbon isotope composition) with P–T constraints from their host rocks, we demonstrate that the peak P–T conditions for the diamond-bearing UHP rocks cluster along water activity-related phase transitions that determine the microdiamond features. With increasing temperature, the diamond-forming medium changes from aqueous fluid to hydrous melt, and diamond morphology evolves from cubo-octahedral to octahedral. The latter is restricted to the UHP-UHT rocks exceeding 1100 °C, which is above the incongruent melting of phengite, where microdiamonds nucleate along a prograde P–T path in silicate-carbonate hydrous melt. The observed effect of temperature on diamond morphology supports experimental data on diamond growth and can be used for examining growth conditions of cratonic diamonds from kimberlites, which are dominated by octahedra and their resorbed forms.J. KotkováY. FedortchoukR. WirthM. J. WhitehouseNature PortfolioarticleMedicineRScienceQENScientific Reports, Vol 11, Iss 1, Pp 1-13 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q J. Kotková Y. Fedortchouk R. Wirth M. J. Whitehouse Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature
description	Abstract Metamorphic diamonds hosted by major and accessory phases in ultrahigh-pressure (UHP) metamorphic terranes represent important indicators of deep subduction and exhumation of continental crust at convergent plate boundaries. However, their nucleation and growth mechanisms are not well understood due to their small size and diversity. The Bohemian microdiamond samples represent a unique occurrence of monocrystalline octahedral and polycrystalline cubo-octahedral microdiamonds in two different metasedimentary rock types. By combining new and published data on microdiamonds (morphology, resorption, associated phases, carbon isotope composition) with P–T constraints from their host rocks, we demonstrate that the peak P–T conditions for the diamond-bearing UHP rocks cluster along water activity-related phase transitions that determine the microdiamond features. With increasing temperature, the diamond-forming medium changes from aqueous fluid to hydrous melt, and diamond morphology evolves from cubo-octahedral to octahedral. The latter is restricted to the UHP-UHT rocks exceeding 1100 °C, which is above the incongruent melting of phengite, where microdiamonds nucleate along a prograde P–T path in silicate-carbonate hydrous melt. The observed effect of temperature on diamond morphology supports experimental data on diamond growth and can be used for examining growth conditions of cratonic diamonds from kimberlites, which are dominated by octahedra and their resorbed forms.
format	article
author	J. Kotková Y. Fedortchouk R. Wirth M. J. Whitehouse
author_facet	J. Kotková Y. Fedortchouk R. Wirth M. J. Whitehouse
author_sort	J. Kotková
title	Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature
title_short	Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature
title_full	Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature
title_fullStr	Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature
title_full_unstemmed	Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature
title_sort	metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature
publisher	Nature Portfolio
publishDate	2021
url	https://doaj.org/article/f6d5b5892a714f4e89311eb149504134
work_keys_str_mv	AT jkotkova metamorphicmicrodiamondformationiscontrolledbywateractivityphasetransitionsandtemperature AT yfedortchouk metamorphicmicrodiamondformationiscontrolledbywateractivityphasetransitionsandtemperature AT rwirth metamorphicmicrodiamondformationiscontrolledbywateractivityphasetransitionsandtemperature AT mjwhitehouse metamorphicmicrodiamondformationiscontrolledbywateractivityphasetransitionsandtemperature
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Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature

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