Electron backscatter diffraction (EBSD) study of seven heavily metamorphosed chondrites: Deformation systematics and variations in pre-shock temperature and post-shock annealing

Absence of olivine orientation fabric in highly shocked Martian dunite

“…b) shows the misorientation of each measured data point relative to the first measured point and reveals large orientation changes that correspond sharply to the grain boundaries, indicating substantial differences in neighboring grain orientations. Intragrain misorientation remains within a range of 5–10° with signs of warping, as described by Ruzicka and Hugo (). The second set of profiles (Fig.…”

“…; Rubin and Swindle ; Lindgren et al. ; Ruzicka and Hugo ); the latter seemingly in contrast with the low shock stage classifications (S1–S2) of many of the studied chondrites. This paradox is resolved by the results of matrix‐based structural studies (Scott et al.…”

“…Nevertheless, an essential feature in rock deformation is conspicuously absent in the list of shock criteria in meteorites: Preferred orientation fabrics, such as shape-preferred orientation (SPO) involving the orientation of the grains themselves and lattice-preferred orientation (LPO) involving the slip of specific crystallographic planes in a preferred direction. Several structural studies of chondrites have identified deformed chondrules and grain alignment fabrics and have attributed these to burial (Cain et al 1986;Zolensky et al 1997) or shock impact (Scott et al 1992;Rubin and Swindle 2011;Lindgren et al 2015;Ruzicka and Hugo 2018); the latter seemingly in contrast with the low shock stage classifications (S1-S2) of many of the studied chondrites. This paradox is resolved by the results of matrix-based structural studies (Scott et al 1992;Nakamura et al 1995;Watt et al 2006;Forman et al 2016Forman et al , 2017 concluding that chondrule deformation and alignment occurs through impact-induced reduction in matrix porosity through pore collapse with consequential matrix compaction.…”

“…; Ruzicka et al. ; Tomioka and Miyahara ; Ruzicka and Hugo ), and computational simulations (e.g., Baer and Trott ) have addressed the effects of shock exposure. The most common macroscopic and microscopic manifestations of shock wave exposure in meteorites are deformational, transformational, or a combination of both (Sharp and DeCarli ).…”

“…The observable effects of such shock exposure are numerous and varied, depending not only on collisional parameters but also on the nature and composition of the target rock, the in situ surroundings and depth of the ejected meteorite, and the distinguishing behavior of constituent phases in reaction to shock wave subjection. Many studies, based on experimental results (St€ offler et al [1991] and references therein), natural observations (Chen et al 1996;Sharp 1997;Langenhorst and Greshake 1999;Langenhorst and Poirier 2000;Xie et al 2006;Zhang et al 2006;Bl€ aß et al 2010;Acosta-Maeda et al 2013;Ruzicka et al 2015;Tomioka and Miyahara 2017;Ruzicka and Hugo 2018), and computational simulations (e.g., Baer and Trott 2002) have addressed the effects of shock exposure. The most common macroscopic and microscopic manifestations of shock wave exposure in meteorites are deformational, transformational, or a combination of both .…”