Shock Metamorphism in the Carswell Circular Structure, Saskatchewan, Canada

Abstract

PETROGRAPHICAL features such as multiple sets of deformation lamellae in quartz, isotropic quartz and feldspar, and characteristic microfracture patterns, are generally believed to be diagnostic of hyper-velocity impact1. These features can be produced experimentally by shock pressures of tens or hundreds of kilobars, which, it is assumed, can only be generated in nature by the hyper-velocity impact of large missiles. All these features occur in the Carswell circular structure, however, in circumstances which cast doubt on this theory.