On the formation of diaplectic glass: Shock and thermal experiments with plagioclase of different chemical compositions

1,2Jörg Fritz,3,4Vera Assis Fernandes,3Ansgar Greshake,5Andreas Holzwarth,6Ute Böttger
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13289]
1Saalbau Weltraum Projekt, Liebigstraße 6, 64646 Heppenheim, Germany
2Zentrum für Rieskrater und Impaktforschung Nördlingen (ZERIN), Vordere Gerbergasse 3, 86720 Nördlingen, Germany
3Museum für Naturkunde, Leibniz Institut für Biodiversität und Evolutionsforschung, Invalidenstraße 43, 10115 Berlin, Germany
4School of Earth and Environmental Science, University of Manchester, Oxford Road, Manchester, M13 9PL UK
5Ernst Mach Institut für Kurzzeitdynamik, Fraunhofer Institut, Am Klingenberg 1, 79588 Efringen‐Kirchen, Germany
6Institut für Optische Sensoren Systeme, Deutsches Zentrum für Luft und Raumfahrt (DLR), Rutherfordstr. 2, 12489 Berlin, Germany
Published by arrangement with John Wiley & Sons

This contribution addresses the role of chemical composition, pressure, temperature, and time during the shock transformation of plagioclase into diaplectic glass—i.e., maskelynite. Plagioclase of An50‐57 and An94 was recovered as almost fully isotropic maskelynite from room temperature shock experiments at 28 and 24 GPa. The refractive index (RI) decreased to values of a quenched mineral glass for An50‐57 plagioclase shocked to 45 GPa and shows a maximum in An94 plagioclase shocked to 41.5 GPa. The An94 plagioclase experiments can serve as shock thermobarometer for lunar highland rocks and howardite, eucrite, and diogenite meteorites. Shock experiments at 28, 32, 36, and 45 GPa and initial temperatures of 77 and 293 K on plagioclase (An50‐57) produced materials with identical optical and Raman spectroscopic properties. In the low temperature (<540 K) region, the formation of maskelynite is entirely controlled by shock pressure. The RI of maskelynite decreased in heating experiments of 5 min at temperatures of >770 K, thus, providing a conservative upper limit for the postshock temperature history of the rock. Although shock recovery experiments and static pressure experiments differ by nine orders of magnitude in typical time scale (microseconds versus hours), the amorphization of plagioclase occurs at similar pressure and temperature conditions with both methods. The experimental shock calibration of plagioclase can, together with other minerals, be used as shock thermobarometer for naturally shocked rocks.

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