Low‐temperature dissociation of zircon in highly alkaline conditions: A cautionary note for studies on natural glasses of debated origin
Résumé
Dissociated zircon is largely used as a robust indicator of glasses generated by impact cratering and airbursts. The reaction of zircon dissociation, i.e. 'ZrSiO4 → ZrO2 + SiO2', requires high temperatures (>1670°C) only reached by extreme geological processes. Using high-temperature experiments, this study shows that zircon can dissociate and form ZrO2-rich coronitic rims at temperatures of 900-1000°C (P = 1 bar), in the presence of a specific chemical environment made of NaCl or a mixture of NaCl and caliche soil (Ca-sulfates). The use of silica glass vessels provides a SiO2-rich environment during the experiments. We observe that the dissociation is strongly related to the complexity of the surrounding system (e.g. the presence of other minerals that act as a flux) in which the reaction occurs. For these reasons, we suggest considering a more careful approach in using dissociated zircon as indicative of very high temperatures in glass-forming processes.
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