The Role of Post-Shock Heating by Plastic Deformation During Impact Devolatilization of Calcite (CaCO3)

An accurate understanding of the relationship between the impact conditions and the degree of shock-induced thermal metamorphism in meteorites allows the impact environment in the early Solar System to be understood. A recent hydrocode has revealed that impact heating is much higher than previously thought. This is because plastic deformation of the shocked rocks causes further heating during decompression, which is termed post-shock heating. Here we compare impact simulations with laboratory experiments on the impact devolatilization of calcite to investigate whether the post-shock heating is also significant in natural samples. We calculated the mass of CO2 produced from the calcite, based on thermodynamics. We found that iSALE can reproduce the devolatilization behavior for rocks with the strength of calcite. In contrast, the calculated masses of CO2 at lower rock strengths are systematically smaller than the experimental values. Our results require a reassessment of the interpretation of thermal metamorphism in meteorites. Plain Language Summary Shock-induced thermal metamorphism found in meteorites could be used as the Rossetta stone, which records the ancient impact environment in the Solar System. If we could understand impact heating, then it would be possible to decode the impact history of the Solar System. We show that the temperature increase after impact events is much higher than conventionally thought, if we consider a recently realized heat source, that is post-shock heating due to shear deformation. Impact simulations were compared with a previous experiment on the impact devolatilization of natural calcite marble to explore the influence of shear deformation on heating. The simulation reproduces the devolatilization behavior of calcite with increasing impact velocity, which demonstrates that heating due to plastic deformation is also significant in natural samples as shown in idealized numerical models. This finding suggests that mutual collisions between planetesimals, which are parent bodies of meteorites, could much easily produce shock-induced thermal metamorphism in rocky materials than previously expected. Consequently, our Solar system might not have a number of dynamically excited bodies.

Automated summary

An accurate understanding of the relationship between impact conditions and shock-induced thermal metamorphism in meteorites is crucial for interpreting the early Solar System's impact environment. Recent hydrocode simulations have shown that post-shock heating from plastic deformation causes higher impact heating than previously believed. By comparing impact simulations and laboratory experiments, researchers found that post-shock heating is significant in natural samples, leading to a reassessment of thermal metamorphism in meteorites.