Three sets of crystallographic sub-planar structures in quartz formed by tectonic deformation

•Multiple tectonic fine extinction bands (FEBs) per grain are common.•Tectonic FEBs can be parallel to the basal, γ, ω, and π crystallographic planes.•Both FEBs and shock induced planar deformation features (PDFs) share these characteristics.•Only planarity diagnostic for PDFs with light microscopy.

In quartz, multiple sets of fine planar deformation microstructures that have specific crystallographic orientations parallel to planes with low Miller-Bravais indices are commonly considered as shock-induced planar deformation features (PDFs)1 diagnostic of shock metamorphism. Using polarized light microscopy, we demonstrate that up to three sets of tectonically induced sub-planar fine extinction bands (FEBs), sub-parallel to the basal, γ, ω, and π crystallographic planes, are common in vein quartz in low-grade tectonometamorphic settings. We conclude that the observation of multiple (2-3) sets of fine scale, closely spaced, crystallographically controlled, sub-planar microstructures is not sufficient to unambiguously distinguish PDFs from tectonic FEBs.

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