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      Fossilized Melts in Mantle Wedge Peridotites

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          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 K 2O = 5.2 wt.%, CaO = 17 wt.%, MgO = 18 wt.%, CO 2 = 22 wt.%, and SiO 2 = 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.

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          Abbreviations for names of rock-forming minerals

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            Some remarks on the movement of small melt fractions in the mantle

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              Thermal structure of oceanic and continental lithosphere

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                Author and article information

                Contributors
                naemura@num.nagoya-u.ac.jp
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                4 July 2018
                4 July 2018
                2018
                : 8
                : 10116
                Affiliations
                [1 ]ISNI 0000 0000 9235 7234, GRID grid.474832.e, Nagoya University Museum, Furo-cho, ; Chikusa-ku, Nagoya 464-8601 Japan
                [2 ]ISNI 0000 0001 2151 536X, GRID grid.26999.3d, Department of Earth and Planetary Science, Graduate School of Science, , The University of Tokyo, 7-3-1 Hongo, ; Bunkyo-ku, Tokyo 113-0033 Japan
                [3 ]ISNI 0000 0004 0372 2033, GRID grid.258799.8, Division of Earth and Planetary Sciences, Graduate School of Science, , Kyoto University, Kitashirakawa Oiwake-cho, ; Sakyo-ku, Kyoto 606-8502 Japan
                [4 ]Institute of Geology of the Czech Academy of Sciences, Rozvojová 269, 165 00, Praha - Lysolaje, Czech Republic
                Article
                28264
                10.1038/s41598-018-28264-6
                6031665
                29973610
                b1aa526b-648e-438a-8f01-4a387e5268d6
                © The Author(s) 2018

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 19 April 2017
                : 11 June 2018
                Funding
                Funded by: FundRef https://doi.org/10.13039/501100001691, Japan Society for the Promotion of Science (JSPS);
                Award ID: 248040
                Award ID: 14403013
                Award ID: 25257208
                Award ID: 21109005
                Award Recipient :
                Funded by: FundRef https://doi.org/10.13039/501100004240, Akademie V&amp;#x011B;d &amp;#x010C;esk&amp;#x00E9; Republiky (Academy of Sciences of the Czech Republic);
                Award ID: M100131203
                Award Recipient :
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