Volatiles Under Shock: Insights from Asteroids and Mars

Volatile-bearing minerals in meteorites preserve chemical and isotopic records of geological processes that have shaped asteroids and planets. However, these records can be modified by subsequent impact-induced metamorphism, complicating interpretations of planetary volatile reservoirs. Although shock metamorphism is widespread in planetary materials, its effects on volatile distributions and isotopic compositions remain poorly constrained, particularly in minerals that retain their crystalline structure. In this seminar, I investigate the effects of shock metamorphism on volatile-bearing minerals from asteroids and Mars by combining scanning and transmission electron microscopy with chemical and isotopic analyses. I first examine carbonates in CM carbonaceous chondrites, where nanoscale deformation microstructures reveal shock histories that are not adequately captured by conventional petrographic classifications. I then investigate phosphates in ordinary chondrites and samples returned from asteroid Itokawa, showing how shock deformation, localized melting, and thermal overprinting produce heterogeneous microstructural and chemical modifications. These observations indicate that volatile elements can be redistributed at the submicrometer scale without necessarily being lost from the mineral. Finally, I examine apatite in the Martian meteorite Los Angeles, where hydrogen-isotope compositions vary with deformation-related defect densities and localized melting, despite comparatively unchanged water contents. This demonstrates that substantial isotopic modification can occur without complete melting or recrystallization.

These studies show that shock-induced modifications can be highly localized and may not be apparent from bulk chemical measurements or conventional petrographic observations. Therefore, the preservation of a mineral’s crystalline structure or volatile abundance does not necessarily imply preservation of its original isotopic composition. Recognizing these effects is essential for interpreting volatile records in meteorites and returned planetary samples, and for reconstructing the evolution of volatile reservoirs on asteroids and Mars.