Fossilized Melts in Mantle Wedge Peridotites

Abstract The shallow oxidized asthenosphere may contain a small fraction of potassic silicate melts that are enriched in incompatible trace elements and volatiles. Here, to determine the chemical composition of such melt, we analysed fossilized melt inclusions, preserved as multiphase solid inclusio...

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Autores principales:	Kosuke Naemura, Takao Hirajima, Martin Svojtka, Ichiko Shimizu, Tsuyosi Iizuka
Formato:	article
Lenguaje:	EN
Publicado:	Nature Portfolio 2018
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/9c44343b5e2049ae8d90e2c2d81bd833
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spelling	oai:doaj.org-article:9c44343b5e2049ae8d90e2c2d81bd8332021-12-02T11:40:45ZFossilized Melts in Mantle Wedge Peridotites10.1038/s41598-018-28264-62045-2322https://doaj.org/article/9c44343b5e2049ae8d90e2c2d81bd8332018-07-01T00:00:00Zhttps://doi.org/10.1038/s41598-018-28264-6https://doaj.org/toc/2045-2322Abstract The shallow oxidized asthenosphere may contain a small fraction of potassic silicate melts that are enriched in incompatible trace elements and volatiles. Here, to determine the chemical composition of such melt, we analysed fossilized melt inclusions, preserved as multiphase solid inclusions, from an orogenic garnet peridotite in the Bohemian Massif. Garnet-poor (2 vol.%) peridotite preserves inclusions of carbonated potassic silicate melt within Zn-poor chromite (<400 ppm) in the clinopyroxene-free harzburgite assemblage that equilibrated within the hot mantle wedge (Stage 1, > 1180 °C at 3 GPa). The carbonated potassic silicate melt, which has a major element oxide chemical composition of K2O = 5.2 wt.%, CaO = 17 wt.%, MgO = 18 wt.%, CO2 = 22 wt.%, and SiO2 = 20 wt.%, contains extremely high concentrations of large ion lithophile elements, similar to kimberlite melts. Peridotites cooled down to ≅800 °C during Stage 2, resulted in the growth of garnet relatively poor in pyrope content, molar Mg/(Mg + Fe + Ca + Mn), (ca. 67 mol.%). This garnet displays a sinusoidal REE pattern that formed in equilibrium with carbonatitic fluid. Subsequently, subduction of the peridotite resulted in the formation of garnet with a slightly higher pyrope content (70 mol.%) during the Variscan subduction Stage 3 (950 °C, 2.9 GPa). These data suggest the following scenario for the generation of melt in the mantle wedge. Primarily, infiltration of sediment-derived potassic carbonatite melt into the deep mantle wedge resulted in the growth of phlogopite and carbonate/diamond. Formation of volatile-bearing minerals lowered the density and strength of the peridotite. Finally, phlogopite-bearing carbonated peridotite rose as diapirs in the mantle wedge to form carbonated potassic silicate melts at the base of the overriding lithosphere.Kosuke NaemuraTakao HirajimaMartin SvojtkaIchiko ShimizuTsuyosi IizukaNature PortfolioarticleMedicineRScienceQENScientific Reports, Vol 8, Iss 1, Pp 1-12 (2018)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q Kosuke Naemura Takao Hirajima Martin Svojtka Ichiko Shimizu Tsuyosi Iizuka Fossilized Melts in Mantle Wedge Peridotites
description	Abstract The shallow oxidized asthenosphere may contain a small fraction of potassic silicate melts that are enriched in incompatible trace elements and volatiles. Here, to determine the chemical composition of such melt, we analysed fossilized melt inclusions, preserved as multiphase solid inclusions, from an orogenic garnet peridotite in the Bohemian Massif. Garnet-poor (2 vol.%) peridotite preserves inclusions of carbonated potassic silicate melt within Zn-poor chromite (<400 ppm) in the clinopyroxene-free harzburgite assemblage that equilibrated within the hot mantle wedge (Stage 1, > 1180 °C at 3 GPa). The carbonated potassic silicate melt, which has a major element oxide chemical composition of K2O = 5.2 wt.%, CaO = 17 wt.%, MgO = 18 wt.%, CO2 = 22 wt.%, and SiO2 = 20 wt.%, contains extremely high concentrations of large ion lithophile elements, similar to kimberlite melts. Peridotites cooled down to ≅800 °C during Stage 2, resulted in the growth of garnet relatively poor in pyrope content, molar Mg/(Mg + Fe + Ca + Mn), (ca. 67 mol.%). This garnet displays a sinusoidal REE pattern that formed in equilibrium with carbonatitic fluid. Subsequently, subduction of the peridotite resulted in the formation of garnet with a slightly higher pyrope content (70 mol.%) during the Variscan subduction Stage 3 (950 °C, 2.9 GPa). These data suggest the following scenario for the generation of melt in the mantle wedge. Primarily, infiltration of sediment-derived potassic carbonatite melt into the deep mantle wedge resulted in the growth of phlogopite and carbonate/diamond. Formation of volatile-bearing minerals lowered the density and strength of the peridotite. Finally, phlogopite-bearing carbonated peridotite rose as diapirs in the mantle wedge to form carbonated potassic silicate melts at the base of the overriding lithosphere.
format	article
author	Kosuke Naemura Takao Hirajima Martin Svojtka Ichiko Shimizu Tsuyosi Iizuka
author_facet	Kosuke Naemura Takao Hirajima Martin Svojtka Ichiko Shimizu Tsuyosi Iizuka
author_sort	Kosuke Naemura
title	Fossilized Melts in Mantle Wedge Peridotites
title_short	Fossilized Melts in Mantle Wedge Peridotites
title_full	Fossilized Melts in Mantle Wedge Peridotites
title_fullStr	Fossilized Melts in Mantle Wedge Peridotites
title_full_unstemmed	Fossilized Melts in Mantle Wedge Peridotites
title_sort	fossilized melts in mantle wedge peridotites
publisher	Nature Portfolio
publishDate	2018
url	https://doaj.org/article/9c44343b5e2049ae8d90e2c2d81bd833
work_keys_str_mv	AT kosukenaemura fossilizedmeltsinmantlewedgeperidotites AT takaohirajima fossilizedmeltsinmantlewedgeperidotites AT martinsvojtka fossilizedmeltsinmantlewedgeperidotites AT ichikoshimizu fossilizedmeltsinmantlewedgeperidotites AT tsuyosiiizuka fossilizedmeltsinmantlewedgeperidotites
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Fossilized Melts in Mantle Wedge Peridotites

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