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Mullite in Libyan Desert Glass: Evidence for high-temperature/low-pressure formation

Greshake, Ansgar and Wirth, Richard and Fritz, Jörg and Jakubowski, Tomasz and Böttger, Ute (2017) Mullite in Libyan Desert Glass: Evidence for high-temperature/low-pressure formation. Meteoritics & Planetary Science. Wiley. DOI: 10.1111/maps.13030 ISSN 1086-9379

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Abstract

Libyan Desert Glass (LDG) is a SiO2-rich natural glass whose origin, formation mechanism, and target material are highly debated. We here report on the finding of a lens-shaped whitish inclusion within LDG. The object is dominantly composed of siliceous glass and separated from the surrounding LDG by numerous cristobalite grains. Within cristobalite, several regions rich in mullite often associated with ilmenite were detected. Mineral assemblage, chemical composition, and grain morphologies suggest that mullite was formed by thermal decomposition of kaolinitic clay at atmospheric pressure and T ≥ 1600 °C and also attested to high cooling rates under nonequilibrium conditions. Cristobalite contains concentric and irregular internal cracks and is intensely twinned, indicating that first crystallized β-cristobalite inverted to α-cristobalite during cooling of the SiO2-rich melt. The accompanied volume reduction of 4% induced the high density of defects. The whitish inclusion also contains several partly molten rutile grains evidencing that at least locally the LDG melt was at T ≥ 1800 °C. Based on these observations, it is concluded that LDG was formed by high-temperature melting of kaolinitic clay-, rutile-, and ilmenite-bearing Cenozoic sandstone or sand very likely during an asteroid or comet impact onto Earth. While melting and ejection occurred at high pressures, the melt solidified quickly at atmospheric pressure.

Item URL in elib:https://elib.dlr.de/119067/
Document Type:Article
Title:Mullite in Libyan Desert Glass: Evidence for high-temperature/low-pressure formation
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Greshake, AnsgarMuseum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germanyhttps://orcid.org/0000-0001-6475-9751
Wirth, RichardHelmholtz Centre Potsdam, GFZ German Research Center for Geosciences, Potsdam, GermanyUNSPECIFIED
Fritz, JörgSaalbau Weltraum Projekt, Heppenheim, GermanyUNSPECIFIED
Jakubowski, TomaszWroclaw, PolandUNSPECIFIED
Böttger, UteInstitut für Optische SensorsystemeUNSPECIFIED
Date:25 December 2017
Journal or Publication Title:Meteoritics & Planetary Science
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
DOI :10.1111/maps.13030
Publisher:Wiley
ISSN:1086-9379
Status:Published
Keywords:Libyan Desert Glass
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Science and Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Erforschung des Weltraums
DLR - Research theme (Project):R - Explorationsstudien
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Optical Sensor Systems > Terahertz and Laser Spectroscopy
Deposited By: Böttger, Dr.rer.nat. Ute
Deposited On:23 Feb 2018 10:23
Last Modified:06 Sep 2019 15:16

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