A study of shock-metamorphic features in zircon from the Siljan impact structure, Sweden

Sammanfattning: Shock-metamorphic features such as planar deformation features (PDFs) and in some cases planar fractures (PFs) are widely used as impact-indicators when to confirm a suspected impact structure. These features only develop when exposed to a sudden and immense pressure and temperature increase in association with meteorite impacts. In previous studies, quartz and k-feldspar containing PDFs have been found at the Siljan impact structure, and the quartz samples enabled an approximation of different shock-zones and the craters original size. In this study, the potential shock-metamorphic effects in the mineral zircon are investigated through scanning electron microscopy (SEM). The samples originate from the Siljan impact structure and are of Järna-granite type. All samples contained planar microstructures, and some of these are assumed to be PDFs based on observations of so called decorations in the lamellae. The nomenclature on shock-features in zircon is not well established and needs further discussion. However, the findings in this study are in most cases comparable to findings of microstructures in zircon from other impact structures.