Experimental Shock Compression of Rocks

We start with a brief summary of the laboratory studies, which motivated the present numerical work. In these experiments (Kenkmann et al. 2000) sized-sized two-component cylindrical rock samples were enclosed in an iron container and impacted by an iron flyer plate at 2540 m/s. The experimental setup is shown schematically in Fig. 1. The individual samples consisted of two lithologies, namely quartzite and dunite, which have been chosen because they show a strong contrast in their behavior under compression. The rock sections were fitted together along a smooth planar interface of varying orientation with respect to the plane of the incoming shock wave. Cross-sections of the samples after the experiments are shown in Fig. 2. In these experiments, gradients in deformation have been found in the two rock sections with decreasing distance from the lithological interface: Fracturing, comminution, and mosaicism are observed in the dunite section, and become more prominent near the

Fig. 1. Experimental setup. By means of an explosive, a driver (flyer plate) is forced onto the sample, which is enclosed in an iron container.

interface. A reduction in birefringence and multiple sets of planar deformation features are characteristic for the quartzite section, both become more intensive towards the interfaces. The occurrence of diaplectic glass, which was formed in one experiment, is restricted to the vicinity of the interface. Melts of a few micrometer width lubricated the lithological interface itself (see Fig. 3). Neutron and synchrotron radiation measurements (Walther et al. 2002, Kenkmann et al. 2003) on the shock deformed samples showed that the crystallite size in the quartzite section decreases with decreasing distance from the interface. The residual strain in olivine of the dunite section increases with decreasing distance from the interface. No high-pressure phases have been found in the recovered samples. The melt formation was attributed to a combination of shock heating and frictional heating.

The melt formation (at least part of it) is proposed by Kenkmann et al. (2000) to occur in the compressed state. Note that the melting point at high pressure is well above the melting point at normal pressure referred to by Kenkmann et al. (2000). We discuss this point briefly at the end of the paper.

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