Shock Recovery With Decaying Compressive Pulses: Shock Effects in Calcite (CaCO₃) Around the Hugoniot Elastic Limit

Abstract

Shock metamorphism of minerals in meteorites provides insights into the ancient Solar System.Calcite is an abundant aqueous alteration mineral in carbonaceous chondrites. Return samples from the asteroids Ryugu and Bennu are expected to contain calcite-group minerals. Although shock metamorphism in silicates has been well studied, such data for aqueous alteration minerals are limited.Here, we investigated the shock effects in calcite with marble using impact experiments at the Planetary Exploration Research Center of Chiba Institute of Technology. We produced decaying compressive pulses with a smaller projectile than the target. A metal container facilitates recovery of a sample that retains its pre-impact stratigraphy. We estimated the peak pressure distributions in the samples with the iSALE shock physics code. The capability of this method to produce shocked grains that have experienced different degrees of metamorphism from a single experiment is an advantage over conventional uniaxial shock recovery experiments. The shocked samples were investigated by polarizing microscopy and X-ray diffraction analysis. We found that more than half of calcite grains exhibit undulatory extinction when peak pressure exceeds 3 GPa. This shock pressure is one order of magnitude higher than the Hugoniot elastic limit (HEL) of marble, but it is close to the HEL of a calcite crystal, suggesting that the undulatory extinction records dislocation-induced plastic deformation in the crystal. Finally, we propose a strategy to re-construct the maximum depth of calcite grains in a meteorite parent body, if shocked calcite grains are identified in chondrites and/or return samples from Ryugu and Bennu.

Experimental Evidence for Shear‐Induced Melting and Generation of Stishovite in Granite at Low (<18 GPa) Shock Pressure

“…Impact‐cratering experiments with two‐stage light‐gas guns, on the other hand, are typically afflicted with the excavation of shocked material from the growing transient crater, which makes the reconstruction of the pre‐impact positions and therefore the peak pressures and temperatures experienced in specific parts of the target challenging (e.g., Wünnemann et al., 2016). With some exceptions (e.g., Hamann et al., 2016; Kohout et al., 2020; Kurosawa et al., 2022; Nagaki et al., 2016), direct transitions between shock stages that form as a result of a continuously decaying shock wave have therefore rarely been studied. Excavation of fragmented and brecciated material in cratering experiments also makes it difficult to assess the amount and mode of local shear‐induced melting at bulk peak pressures far below those typically required for incipient melting (e.g., Kenkmann et al., 2000; Langenhorst et al., 2002).…”

Experimentally Shock‐Induced Melt Veins in Basalt: Improving the Shock Classification of Eucrites

“…The experimental method employed in this study is basically the same as that developed by Kurosawa et al. (2022), except for the samples that were used. The method allows us to collect shocked samples that retain the pre‐impact stratigraphy.…”

“…A shock recovery experiment was conducted with a two-stage light gas gun at the Planetary Exploration Research Center of the Chiba Institute of Technology, Japan (Kurosawa et al, 2015). The experimental method employed in this study is basically the same as that developed by Kurosawa et al (2022), except for the samples that were used. The method allows us to collect shocked samples that retain the pre-impact stratigraphy.…”

“…We conducted numerical calculations using the same impact conditions as the experiments using the two-dimensional version of the iSALE shock physics code (Amsden et al, 1980;Collins et al, 2016;Ivanov et al, 1997;Wünnemann et al, 2006), in order to estimate the peak pressure and peak temperature distributions in the shocked samples. The model settings and material model parameters were basically the same as used in Kurosawa et al (2022), except that the target material was basalt used in the present study. As such, we used the ANalytical Equations of State (ANEOS basalt) (Pierazzo et al, 2005;Sato et al, 2021;Thompson & Lauson, 1972) and rock strength model (Collins et al, 2004) for basalt (Bowling et al, 2020;Ivanov et al, 2010) in this study.…”

“…In this study, we conducted shock recovery experiments with terrestrial basalt blocks using a recently developed technique (Kurosawa et al., 2022), which allows collection of shocked samples that have experienced a range of peak pressures and temperatures. The position‐dependent peak pressures and temperatures were estimated by shock physics modeling.…”