4:30 PM - 4:45 PM
[SCG49-05] High strain rate deformation experiments of calcite and estimates of yield stress and temperature increase under impact conditions
Keywords:calcite, deformation experiment, high strain rate, impact, yield strength, Post-shock heating
Meteorite impacts are a universal phenomenon for astronomical bodies and are key to understanding Earth's history. For example, a meteorite impact that created the K/Pg boundary had a major impact on the Earth's environment and life. It has been suggested that the impact devolatilization of calcite by the meteorite impact largely influenced the environment (e.g., O’Keefe and Ahrens, 1989). The temperature increase and devolatilization of calcite due to impact have been evaluated from impact experiments and numerical simulations. Recent previous study pointed out the importance of post-shock heating in temperature increase (Kurosawa et al., 2021). Kurosawa et al. (2021) indicated that the post-shock heating and devolatilization of calcite depends on the yield strength of the target in numerical calculations using iSALE. Moreover, a comparison between the numerical and experimental results suggests that the yield strength of calcite under impact conditions might be 3-4 times higher than the yield strength suggested in previous study (Goldin et al., 2006). In this study, we conducted deformation experiments of calcite at high strain rates, and the constrained flow law was used to estimate the yield strength of calcite and the temperature increase due to the post-shock heating under the impact conditions.
Deformation experiments of calcite were conducted using a Griggs-type deformation apparatus at the Kochi Core Center. The experimental conditions were a temperature of 400 ºC, confining pressures of 0.75-1.5 GPa and strain rates of 1.0×10-4–1.0×10-2 s-1. The yield strength of calcite at each pressure and strain rate was determined from the stress-strain curves of our deformation experiments. A pressure dependence and a strain-rate dependence of the yield strength were observed in the experimental results. From the variation of the stress exponent obtained from the results, we concluded that the deformation mechanism of calcite changed from power-law creep to Peierls creep at differential stress of 350 MPa. Based on these experimental results, the activation volume V* = 11.8 ± 2.7 cm3/mol, the constant A = 107.62, and the Peierls stress σp = 3645 MPa in the flow law of Peierls creep on calcite were determined, respectively.
We estimated the yield strength of calcite and the temperature increase of the post-shock heating under natural impact conditions (>10 GPa, 100-104 s-1) using the constrained flow law of calcite. The yield strength (1.8-2.7 GPa) calculated from our results is 3-4 times higher than that of calcite suggested in previous study (Goldin et al., 2006), and is similar to that predicted by Kurosawa et al. (2021). The temperature increase of the post-shock heating possibly exceeds 400-800 °C even if the impact pressure is 10-20 GPa, suggesting the importance of the post-shock heating.
Deformation experiments of calcite were conducted using a Griggs-type deformation apparatus at the Kochi Core Center. The experimental conditions were a temperature of 400 ºC, confining pressures of 0.75-1.5 GPa and strain rates of 1.0×10-4–1.0×10-2 s-1. The yield strength of calcite at each pressure and strain rate was determined from the stress-strain curves of our deformation experiments. A pressure dependence and a strain-rate dependence of the yield strength were observed in the experimental results. From the variation of the stress exponent obtained from the results, we concluded that the deformation mechanism of calcite changed from power-law creep to Peierls creep at differential stress of 350 MPa. Based on these experimental results, the activation volume V* = 11.8 ± 2.7 cm3/mol, the constant A = 107.62, and the Peierls stress σp = 3645 MPa in the flow law of Peierls creep on calcite were determined, respectively.
We estimated the yield strength of calcite and the temperature increase of the post-shock heating under natural impact conditions (>10 GPa, 100-104 s-1) using the constrained flow law of calcite. The yield strength (1.8-2.7 GPa) calculated from our results is 3-4 times higher than that of calcite suggested in previous study (Goldin et al., 2006), and is similar to that predicted by Kurosawa et al. (2021). The temperature increase of the post-shock heating possibly exceeds 400-800 °C even if the impact pressure is 10-20 GPa, suggesting the importance of the post-shock heating.