Microscopic lamellar deformation features in quartz: Discriminative characteristics of shock-generated varieties

Abstract

The appearance and orientation of microscopic lamellar deformation features in quartz have been examined in samples from different geologic environments. Lamellar deformation features from known shock and/or impact environments are sharp, parallel, closely spaced, and tend to extend in a continuous manner across entire grains. They have specific, well-documented orientations and occur in multiple sets per grain. Lamellar deformation features from other geologic environments, including tectonic and explosive volcanic, only superficially resemble shock features. They are generally less well defined, slightly curved, wider spaced, and tend to extend in a discontinuous manner across parts of grains. They have relatively random orientations, only some of which correspond to known shock orientations, and generally occur as single sets per grain. On the basis of these observations, we conclude that there is a characteristic set of microscopic deformation features produced in quartz by shock. These so-called planar features differ from microscopic lamellar deformation features produced by other dynamic processes; therefore, the case for the formation of characteristic planar features in quartz by natural processes other than impact is still not proven.