Experimental reproduction of tectonic deformation lamellae in quartz and comparison to shock-induced planar deformation features

Abstract

Planar features can develop in quartz during comparatively slow tectonic deformation and during very fast dynamic shock metamorphism. Despite their very different structural nature, tectonically induced deformation lamellae have sometimes been mistaken as shock-induced planar deformation features (PDFs). To understand the formation of deformation lamellae and to address the substantial differences between them and PDFs, we have conducted deformation experiments on single crystals of quartz in a Griggs-type apparatus, at a temperature of 800 degrees C, a confining pressure of 12 kbar, and a strain rate of 0.7- 1.1 x 10^(-6). The deformed samples were analyzed with transmission electron microscopy (TEM) and compared to natural PDFs from the Ries Crater, Germany. TEM revealed that tectonic deformation lamellae are associated with numerous sub-parallel curved subgrain walls, across which the orientation of the crystal changes slightly. The formation of deformation lamellae is due to glide- and climb-controlled deformation in the exponential creep regime. In contrast, the PDFs in shocked quartz from the Ries are perfectly planar, crystallographically controlled features that originally represented amorphous lamellae. Due to postshock annealing and hydrothermal activity they are recrystallized and decorated with fluid inclusions.