Localized shock-induced melting of sandstone at low shock pressures (<17.5 GPa): An experimental study

1,2Matthias Ebert,2,3Astrid Kowitz,2Ralf Thomas Schmitt,2,4,5Wolf Uwe Reimold,6Ulrich Mansfeld,6Falko Langenhorst
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12948]
1Institut für Geo- und Umweltnaturwissenschaften, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
2Museum für Naturkunde – Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
3Department of Earth Sciences, Freie Universität, Berlin, Germany
4Humboldt Universität zu Berlin, Berlin, Germany
5Geochronology Laboratory, University of Brasilia, Brasilia, Brazil
6Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Jena, Germany
Published by arrangement with John Wiley & Sons

Shock-induced recovery experiments were performed to investigate melt formation in porous sandstones in the low shock pressure regime between 2.5 and 17.5 GPa. The sandstone shocked at 2.5 and 5 GPa is characterized by pore closure, fracturing of quartz (Qtz), and compression and deformation of phyllosilicates; no melting was observed. At higher pressures, five different types of melts were generated around pores and alongside fractures in the sandstone. Melting of kaolinite (Kln), illite (Ill), and muscovite (Ms) starts at 7.5, 12, and 15 GPa, respectively. The larger the amount of water in these minerals (Kln ~14 wt%, Ill ~6–10 wt%, and Ms ~4 wt% H2O), the higher the shock compressibility and the lower the shock pressure required to induce melting. Vesicles in the almost dry silicate glasses attest to the loss of structural water during the short shock duration of the experiment. The compositions of the phyllosilicate-based glasses are identical to the composition of the parental minerals or their mixtures. Thus, this study has demonstrated that phyllosilicates in shocked sandstone undergo congruent melting during shock loading. In experiments at 10 GPa and higher, iron melt from the driver plate was injected into the phyllosilicate melts. During this process, Fe is partitioned from the metal droplets into the surrounding silicate melts, which induced unmixing of silicate melts with different chemical properties (liquid immiscibility). At pressures between 7.5 and 15 GPa, a pure SiO2 glass was formed, which is located as short and thin bands within Qtz grains. These bands were shown to contain tiny crystals of experimentally generated stishovite.

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