Subsurface deformation of experimental hypervelocity impacts in quartzite and marble targets

Abstract

Two impact cratering experiments on nonporous rock targets were carried out to determine the influence of target composition on the structural mechanisms of subsurface deformation. Projectiles of 2.5 mm diameter were accelerated to ~5 km s−1 and impacted onto blocks of marble or quartzite. Subsurface deformation was mapped and analyzed on the microscale using thin sections of the bisected craters. Additionally, both experiments were modeled and the calculated strain zones underneath the craters were compared to experimental deformation features. Microanalysis shows that the formation of radial, tensile, and intragranular cracks is a common response of both nonporous materials to impact cratering. In the quartzite target, the subsurface damage is additionally characterized by highly localized deformation along shear bands with intense grain comminution, surrounded by damage zones. In contrast, the marble target shows closely spaced calcite twinning and cleavage activation. Crater diameter and depth as well as the damage lens underneath the crater are unexpectedly smaller in the marble target compared to the quartzite target, which is in contradiction to the marble's much weaker compressive and tensile strengths. However, numerical models result in craters that are similar in size as well as in strain accumulation at the end of transient crater formation, indicating that current models should still be viewed cautiously when compared to experimental details.

Variation in Magnetic Fabrics at Low Shock Pressure Due to Experimental Impact Cratering

“…The projectiles were accelerated to 7.236 and 6.925 km/s, and the target chamber pressure was 1.7 and 1.9 mbar during the experiment on A38 and A37, respectively. The differences in projectile velocity are expected to not affect the subsurface deformation (Winkler et al, 2018). For details of the accelerator and the exact experimental assembly, refer to Schneider and Schäfer (2001), Poelchau et al (2013), and Kenkmann et al (2018).…”

Experimental impact cratering: A summary of the major results of the MEMIN research unit

“…Very shallow craters were obtained for impacts into marble (Winkler et al. ), while deep penetration tubes were formed by impact into high‐porosity tuff (Winkler et al. , ).…”

“…In the case of the highly porous tuff, an extra‐deep, tube‐like, quasi‐cylindrical cavity developed (Winkler et al. , ) comparable to funneled craters in highly porous snow (Luther et al. , Forthcoming).…”

“…Winkler et al. (, ) carried out a systematic study of target damage for craters in highly porous tuff. Here, the deformation in the subsurface included, among other effects, pore space compaction and clast rotation.…”

“…First-order differences between the various craters were expressed by the craters' depth/diameter ratios ( Table 2) that range from 0.1 to 0.56. Very shallow craters were obtained for impacts into marble (Winkler et al 2016b), while deep penetration tubes were formed by impact into high-porosity tuff (Winkler et al 2016a(Winkler et al , 2016b.…”