| Abstract: | Abstract— Analytical scanning electron microscopy has been used to investigate the surface textures and compositions of newly exposed shatter cones from the 1.85 Ga Sudbury impact structure, Canada. Unusual surface microstructures are observed at the micron scale, including silicate melt smears, melt fibres and melt splats. Silicate and Ni-rich spherules up to 5 μm in diameter adorn earlier-formed surface features, and we interpret these to be condensates formed due to shock-induced vaporization of the shatter cone surfaces. The development of striations on the shatter cones is attributed to shock-related fracture and slip. Formation of melts and spherules indicates that the highest ranks of shock metamorphism (Stages IV and V) were realized, but only on a very localized scale. Shatter cone surfaces are, therefore, likely sites for the development of high-pressure polymorphs and, if the chemistry is appropriate, fullerenes. As such, they may be equivalent to “Type A” pseudotachylytes and shock veins in meteorites. |
