Silica Polymorphs Formation in the Jänisjärvi Impact Structure: Tridymite, Cristobalite, Quartz, Trace Stishovite and Coesite

The study of silica polymorphs in impactites is important for determining the pressure and temperature of impact rock formation. Silica modifications in impact melt rocks of the Janisjärvi impact structure (Karelia, Russia) are presented by tridymite, cristobalite, quartz, trace stishovite and coesi...

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Bibliographic Details
Main Authors: Daria A. Zamiatina, Dmitry A. Zamyatin, Georgii B. Mikhalevskii, Nikolai S. Chebikin
Format: Article in Journal/Newspaper
Language:English
Published: MDPI AG 2023
Subjects:
tridymite
cristobalite
ballen quartz
trace stishovite
trace coesite
impact melt rock
Mineralogy
QE351-399.2
Ballen
Jänisjärvi
karelia*
Online Access:https://doi.org/10.3390/min13050686
https://doaj.org/article/e49ef2e498254760b39c5670e4946c13
Description
Summary:The study of silica polymorphs in impactites is important for determining the pressure and temperature of impact rock formation. Silica modifications in impact melt rocks of the Janisjärvi impact structure (Karelia, Russia) are presented by tridymite, cristobalite, quartz, trace stishovite and coesite. Silica modifications were characterized and studied by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and Raman and cathodoluminescent spectroscopy. Investigations were carried out in order to clarify polymorphs formation mechanisms and search for signs of the transition of certain structural modifications to others. For the first time, a description of tridymite with a ballen-like texture from impact melt rock is given. A sequence of silica modification and textural transformation in impact rocks after the impact event is suggested. We conclude that the pressure of 40 GPa and a temperature of more than 900 °C were achieved in the impact structure.

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