Petrography of impactites from the Dellen impact structure, Sweden

Abstract: Identification and characterization of shock-metamorphic features in hypervelocity impact craters is important for our understanding of how shock waves interact with geologic materials and how impact craters form, which in turn is essential to our understanding of what role impact cratering played in the development of our solar system. Of particular interest are accessory minerals like apatite, which contains various volatiles that can affect the atmosphere of a body, or magnetite whose magnetic properties constitute a remote sensing indicator which allows us to study and understand the internal structures of distant bodies. Understanding how these magnetic properties are affected by shock waves in impacts allows for better modelling and interpretation of data retrieved by remote sensing. This study reports on multiple examples of shock-metamorphic features from allochthonous samples retrieved from the Dellen impact structure, Sweden. Shock-metamorphic features chiefly in apatite and magnetite, but also zircon, titanite, biotite, quartz and feldspar are reported on. Apatite and magnetite grains were both found to show signs of dynamic recrystallization, and apatite also displays tentative micro-vesicles. Other shock-metamorphic features identified include ‘ballen quartz’ and baddeleyite formation in zircon. Some features were also found which may have been induced by the shock waves, but whose origins are unclear, such as exsolution textures in titanite.