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Donwilhelmsite, [CaAl4Si2O11], a new lunar high-pressure Ca-Al-silicate with relevance for subducted terrestrial sediments

Fritz, Jörg and Greshake, Ansgar and Klementova, Mariana and Wirth, Richard and Palatinus, Lukas and Trønnes, Reidar G. and Fernandes, Vera Assis and Böttger, Ute and Ferrière, Ludovic (2020) Donwilhelmsite, [CaAl4Si2O11], a new lunar high-pressure Ca-Al-silicate with relevance for subducted terrestrial sediments. American Mineralogist (105), pp. 1704-1711. Mineralogical Society of America. doi: 10.2138/am-2020-7393. ISSN 0003-004X.

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We report on the occurrence of a new high-pressure Ca-Al-silicate in localized shock melt pockets found in the feldspatic lunar meteorite Oued Awlitis 001 and discuss the implications of our discovery. The new mineral crystallized as tiny, micrometer-sized, acicular grains in shock melt pockets of roughly anorthitic bulk composition. Transmission electron microscopy based three-dimensional electron diffraction (3D ED) reveals that the CaAl4Si2O11 crystals are identical to the calcium aluminum silicate (CAS) phase first reported from static pressure experiments. The new mineral has a hexagonal structure, with a space group of P63/mmc and lattice parameters of a = 5.42(1) Å; c = 12.70(3) Å; V = 323(4) Å3; Z = 2. This is the first time 3D ED was applied to structure determination of an extraterrestrial mineral. The International Mineralogical Association (IMA) has approved this naturally formed CAS phase as the new mineral “donwilhelmsite” [CaAl4Si2O11], honoring the U.S. lunar geologist Don E. Wilhelms. On the Moon, donwilhelmsite can form from the primordial feldspathic crust during impact cratering events. In the feldspatic lunar meteorite Oued Awlitis 001, needles of donwilhelmsite crystallized in ~200 mm sized shock melt pockets of anorthositic-like chemical composition. These melt pockets quenched within milliseconds during declining shock pressures. Shock melt pockets in meteorites serve as natural crucibles mimicking the conditions expected in the Earth’s mantle. Donwilhelmsite forms in the Earth’s mantle during deep recycling of aluminous crustal materials, and is a key host for Al and Ca of subducted sediments in most of the transition zone and the uppermost lower mantle (460–700 km). Donwilhelmsite bridges the gap between kyanite and the Ca-component of clinopyroxene at low pressures and the Al-rich Ca-ferrite phase and Ca-perovskite at high-pressures. In ascending buoyant mantle plumes, at about 460 km depth, donwilhelmsite is expected to break down into minerals such as garnet, kyanite, and clinopyroxene. This process may trigger minor partial melting, releasing a range of incompatible minor and trace elements and contributing to the enriched mantle (EM1 and EM2) components associated with subducted sedimentary lithologies.

Item URL in elib:https://elib.dlr.de/137083/
Document Type:Article
Title:Donwilhelmsite, [CaAl4Si2O11], a new lunar high-pressure Ca-Al-silicate with relevance for subducted terrestrial sediments
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Fritz, JörgUNSPECIFIEDhttps://orcid.org/0000-0002-6333-4775
Greshake, AnsgarMuseum für Naturkunde, Leibniz-Institut an der Humboldt-Universität zu Berlin, Invalidenstraße 43, 10115 Berlin, Germanyhttps://orcid.org/0000-0001-6475-9751
Klementova, MarianaInstitute of Physics of the Czech Academy of ScienceUNSPECIFIED
Wirth, RichardHelmholtz Centre Potsdam, GFZ German Research Center for Geosciences, Potsdam, GermanyUNSPECIFIED
Palatinus, LukasInstitute of Physics of the Czech Academy of ScienceUNSPECIFIED
Trønnes, Reidar G.Natural History Museum and Centre for Earth Evolution and Dynamics (CEED), University of OsloUNSPECIFIED
Fernandes, Vera AssisSchool of Earth and Environmental Science, University of Manchester, Oxford Road, Manchester, M13 9PL UKUNSPECIFIED
Böttger, UteDLR, Institut für Optische SensorsystemeUNSPECIFIED
Ferrière, LudovicNatural History Museum of Vienna, AustriaUNSPECIFIED
Date:2 November 2020
Journal or Publication Title:American Mineralogist
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:Yes
DOI :10.2138/am-2020-7393
Page Range:pp. 1704-1711
Publisher:Mineralogical Society of America
Keywords:High-pressure phase, new mineral, donwilhelmsite, Oued Awlitis 001 lunar meteorite, shock metamorphism, subduction, mantle mineral, enriched mantle component
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Space Exploration
DLR - Research theme (Project):R - Exploration of the Solar System
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Optical Sensor Systems > Space Instruments
Deposited By: Böttger, Dr.rer.nat. Ute
Deposited On:04 Nov 2020 11:13
Last Modified:02 Nov 2021 03:00

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