Nano-scale investigation of granular neoblastic zircon, Vredefort impact structure, South Africa: Evidence for complete shock melting
- Autor(en)
- Elizaveta Kovaleva, Monika Kusiak, Gavin Kenny, Martin J. Whitehouse, Gerlinde Habler, Anja Schreiber, Richard Wirth
- Abstrakt
Granular neoblastic zircon (ZrSiO4) with systematically oriented granules has been proposed as evidence for extreme shock pressures (>30 GPa) and subsequent high temperatures (>1200 degrees C). It is widely agreed to reflect the solid-state phase transition from zircon to its high-pressure polymorph reidite and subsequent reversion to zircon. This model is based on crystallographic relationships between granules of a single type of granular zircon and does not explain the formation of other types of granular zircon textures, for example, grains with randomly oriented granules or with large, often euhedral granules. Here we report the first nano-scale observations of granular neoblastic zircon and the surrounding environment. We conducted combined microstructural analyses of zircon in the lithic clast from an impact melt dike of the Vredefort impact structure. Zircon granules have either random or systematic orientation with three mutually orthogonal directions of their c-axes coincident with [110] axes. Each 1-2 mu m zircon granule is a mosaic crystal composed of nanocrystalline subunits. Granules contain round inclusions of baddeleyite (monoclinic ZrO2) and amorphous silica melt. Tetragonal and cubic ZrO2 also occur as sub-mu m-sized inclusions (
- Organisation(en)
- Department für Lithosphärenforschung
- Externe Organisation(en)
- Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum, University of the Western Cape (UWC), Polish Academy of Sciences (PAS), Swedish Museum of Natural History
- Journal
- Earth and Planetary Science Letters
- Band
- 565
- Anzahl der Seiten
- 15
- ISSN
- 0012-821X
- DOI
- https://doi.org/10.1016/j.epsl.2021.116948
- Publikationsdatum
- 07-2021
- Peer-reviewed
- Ja
- ÖFOS 2012
- 105116 Mineralogie, 105120 Petrologie
- Schlagwörter
- ASJC Scopus Sachgebiete
- Geochemistry and Petrology, Geophysics, Earth and Planetary Sciences (miscellaneous), Space and Planetary Science
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/f465e978-61b2-4bd9-ab22-23af319ad56f