CL “LAMELLAE” IN TECTONICALLY DEFORMED QUARTZ GRAINS

SEM-cathodoluminescence imaging of quartz grains from clasts of a tectonically deformed diamictite along the Willard thrust zone in northern Utah reveals unexpected lamellar features: alternating bands of luminescent and non-luminescent quartz. These lamellae are confined to single grains, and appear in different orientations in neighboring grains. Within some grains, lamellae occur in multiple sets, and are bent by the onset of the second set of lamellae. Most lamellae are roughly 10-20 µm wide. The density of lamellae, measured from the CL images, does not appear to directly correlate to strain, but the footwall samples tend to have a higher density than those from the hanging wall. Average lamellae density values range from 2.6-9.0 lamellae/100 μm. Most differences in luminosity of quartz grains occur due to differences in levels of trace elements, such as titanium. The CL lamellae are particularly intriguing because it is unlikely that trace elements are the cause for differences in luminescence between the lamellae. It is possible that these features are strain-induced, although little work has been done to describe these in the literature. To test this idea, EBSD maps with a bin size of 1µm were conducted on 10 of the grains in which CL lamellae were observed. None of the maps shows significant misorientation of the quartz crystal lattice across the lamellae, leaving the their origin enigmatic.