DISTINGUISHING SHOCKED FROM TECTONICALLY DEFORMED QUARTZ BY THE USE OF THE SEM AND CHEMICAL ETCHING

Multiple sets of crystallographically-oriented planar deformation feat ures (PDFs) are generated by high-strain-rate shock waves at pressures of > 12 GPa in naturally shocked quartz samples. On surfaces, PDFs ap pear as narrow (50-500 nm) lamellae filled with amorphosed quartz (dia plectic glass) which can be etched with hydrofluoric acid or with hydr othermal alkaline solutions. In contrast, slow-strain-rate tectonic de formation pressure produces wider, semi-linear and widely spaced array s of dislocation loops that are not glass filled. Etching samples with HF before examination in a scanning electron microscope (SEM) allows for unambiguous visual distinction between glass-filled PDFs and glass -free tectonic deformation arrays in quartz. This etching also reveals the internal 'pillaring' often characteristic of shock-induced PDFs. This technique is useful for easily distinguishing between shock and t ectonic deformation in quartz, but does not replace optical techniques for characterizing the shock features.