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

Abstract

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 °C, a confining pressure of 12 kbar, and a strain rate of 0.7-1.1 ⋅ 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.

Geophysical anomalies and quartz deformation of the Warburton West structure, central Australia

“…6a), consistent with shock levels of >20 GPa (Stöffler and Langenhorst, 1994;Grieve et al, 1996;French, 1998;Langenhorst, 2002;Vernooij and Langenhorst, 2005;French and Koeberl, 2010). Transmission Electron Microscopy (TEM) analysis displays relic narrow ≤1 μm-wide lamellae which are not regarded as sub grain boundaries and where crystal segments maintain optical continuity, indicating they are not Boehm lamellae.…”

“…Very large impact structures yet to be confirmed include the ~500 km-large Otish Basin, Quebec, containing intracrystalline planar deformation features in quartz and cored by a mafic body (Genest et al, 2011). The identification of impact structures depends critically on microstructural criteria of shock metamorphism (Carter, 1965(Carter, , 1968Carter and Friedman, 1965;Carter et al, 1986;Alexopoulos et al, 1988;Lyons et al, 1993;Grieve et al, 1996;Stöffler and Langenhorst, 1994;Engelhardt et al, 1969;Vernooij and Langenhorst, 2005;Spray and Trepmann, 2006; A C C E P T E D M A N U S C R I P T…”

An extended field of crater-shaped structures in the Gilf Kebir region, Egypt: Observations and hypotheses about their origin

“…Figs. 16c and d display sub-planar optical discontinuities reminiscent of planar fractures (PFs), known from weakly shocked quartz (1-8 GPa pressure range) of many impact structures (Stö ffler and Langenhorst, 1994; Grieve et al, 1996), but also strongly resembling tectonically induced deformation lamellae (Vernooij and Langenhorst, 2005). It must be noted that PFs by themselves are not directly impact-diagnostic, but where they occur in relative abundance, they may provide indication for the possible presence of an impact structure.…”

CO 2 flow during orogenic gravitational collapse: Syntectonic decarbonation and fluid mixing at the ductile-brittle transition (Lavrion, Greece)

“…short trails along deformation lamellae ( Fig.3d; Böhm, 1883;Vernooij and Langenhorst, 2005), or (iv) in planes crosscutting quartz subgrains (Fig.3e). …”