[S-CG46] Rheology, fracture and friction in Earth and planetary sciences

[SCG46-12] Elasto-plastic behavior of carbonate rocks under high strain rate deformation

★Invited Papers

*Kosuke Kurosawa¹, Hidenori Genda², Shintaro Azuma³, Keishi Okazaki⁴, Haruka Oono¹, Takafumi Niihara⁵, Takashi Mikouchi⁶, Naotaka Tomioka⁴, Tatsuhiro Sakaiya⁷, Tadashi Kondo⁷, Masahiro KAYAMA⁸, Mizuho Koike⁹, Yuji Sano¹⁰, Takuya Matsuzaki¹¹, Masafumi MURAYAMA¹¹, wataru Satake¹, Takafumi Matsui^1,12 (1.Planetary Exploration Research Center, Chiba Institute of Technology, 2.Earth–Life Science Institute, Tokyo Institute of Technology, 3.Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 4.Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 5.Department of Systems Innovation, School of Engineering, The University of Tokyo, 6.The University Museum, The University of Tokyo, 7.Department of Earth and Space Science, Graduate School of Science, Osaka University, 8.Department of General Systems Studies, Graduate School of Arts and Sciences, The Univ. of Tokyo, 9.Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 10.Atmosphere and Ocean Research Institute, The University of Tokyo, 11.Center for Advanced Marine Core Research, Kochi University, 12.Institute of Geo-Cosmology, Chiba Institute of Technology)

Keywords:Celestial collisions, calcite, plastic deformation

Impact craters dominate the surface topography of planets/satellites/asteroids with solid surfaces and without atmospheres and hydrospheres. Most of the meteorites found on the Earth contain unique metamorphic features caused by deformation under high stress conditions. These facts are evidence that mutual collisions between planetary bodies are one of the fundamental geological processes in the solar system. In hypervelocity collisions, materials are fluidized and deformed by induced shock waves. The characteristic strain rate of celestial collisions is expressed as the ratio of the impact velocity to the projectile diameter, and it typically exceeds 1 s^-1. In the case of an impact at >10 km/s, shock pressure exceeds 100 GPa, and a temperature rise due to irreversible compression leads to the perfect fluid approximation being valid. Our understanding of impact phenomena has often been based on the perfect fluid approximation. However, the typical impact velocity in the asteroid belt where meteorite parent bodies existed is ~5 km/s, which is comparable to the sound speed of rocky materials, and the elasto-plastic response of shocked rocks during impact events could not be ignored. Recently, Kurosawa and Genda (2018), GRL, 45, 620-626, numerically showed that the degree of impact heating due to plastic deformation during low-velocity impacts (<10 km/s) can be larger than that due to irreversible compression during shock wave propagation. The accurate understanding of the rock rheology is becoming more important in planetary sciences than previously thought.

We have started multifaceted studies to explore the responses of carbonate rocks under deformation with high strain rates. The advantages of the use of carbonate rocks are: (1) the temperature and pressure dependence of yield strength can be expressed by the same empirical law pertaining to igneous rocks, (2) the volatile component (CO2) is released at a relatively low temperature, and the degree of impact heating in the shocked sample can be quantitatively evaluated by measuring the amount of CO2 generated, and (3) homogeneous samples can be obtained at low cost. In this study, Carrara marble from Italy was used as a reference material. The marble constitutes crystallographically randomly-oriented calcite crystals having 100–300 um in diameter without gaps between grains.
In this presentation, we show the importance of the flow law to accurately estimate the amount of CO2 generated from shocked marbles based on the results of numerical impact calculations incorporating a simple rheology model for Calcite [Kurosawa, Genda, Azuma, and Okazaki, Revised]. We also present the results of an on-going shock-recovery experiment with the marble. In our experiments, shocked marbles, which have experienced pressures of 1 - 10 GPa and strain rates of 10^5 – 10^6 s-1, could be recovered for in-depth analyses.