Sem-cl Imaging of Planar Deformation Features and Tectonic Deformation Lamellae in Quartz

Introduction: Planar deformation features (PDFs) in quartz are diagnostic impact evidence. Using light microscopy, it is often impossible to distinguish between PDFs and tectonic deformation lamellae. [1] showed that PDFs can be imaged using a cathodoluminescence (CL) detector in a scanning electron microscope (SEM) and that in SEM-CL images PDFs can be distinguished from tectonic microfractures. However, they did not consider tectonic deformation lamellae. In order to define characteristics that can be used for the distinction between PDFs and tectonic lamellae, we used the SEM-CL technique to image both types of structure. Samples and methods: Amorphous PDFs were studied in fallout suevites from the Ries crater (Germany), annealed and decorated PDFs in lithic breccias from the Rochechouart crater (France) and tectonic deformation lamellae in quartzites from the Flinders Range (Australia). All samples were polished, carbon coated thin sections. A CL-detector mounted on an SEM was used for imaging. Results and discussion: Both PDFs and tectonic deformation lamellae can be imaged very clearly and at high resolution using the SEM-CL technique. Tectonic lamellae from the Flin-ders Range quartzite sample appear as slightly irregular, planar features, ranging in grayscale from black to white. They often occur only in part of a grain and are usually not penetrative through the whole grain. In general, they are thicker and more widely spaced than PDFs. Amorphous PDFs from the Ries crater are visible in CL images as dark, very narrow, densely spaced, perfectly straight and often penetrative planar features. Both etched and unetched PDFs are visible. The decorated PDFs from the Rochechouart crater are also dark, but less penetrative and not as densely spaced as the amorphous type in the Ries samples. Very rarely straight, narrow planar features occur in the Rochechouart samples, that are lighter than the surrounding quartz and are only just visible. These could be annealed, but non-decorated PDFs, but further research is required to confirm this. In general, tectonic lamellae can be distinguished from shock lamellae in CL images. However, especially when lamellae are relatively narrow and straight and when two sets are present, tec-tonic lamellae can resemble PDFs. In these cases, high resolution , high magnification images still show the tectonic lamellae to be wider, slightly irregular and (usually) non-penetrative features. Conclusions: Both PDFs and tectonic deformation lamellae can be imaged with SEM-CL very clearly and at a high resolution. For single grain analysis additional methods are required to unequivocally …