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- Title
EBSD Analysis of Iron‐Nickel Metal in L Type Ordinary Chondrites: 2. Formation of Net, Acicular, Duplex, and Pearlitic Plessite.
- Authors
Luo, Yexin; Chen, Hongyi; Beard, Sky; Zeng, Xiaojia; Hu, Sen; Jin, Lei; Liu, Jiahui; Li, Shaolin; Zhang, Xiaoping
- Abstract
The microstructure of plessite, which is composed of kamacite (α) and taenite (γ), exhibits diverse formation mechanisms and is highly complex. In this study, four types of plessite, namely net, acicular, duplex, and pearlitic plessite, were investigated in L group chondrites using the Electron Backscatter Diffraction (EBSD) technique. This enabled comprehensive determination of their orientation relationships, evolution paths, and formation mechanisms. The findings from this study demonstrate that net plessite is formed due to shock reheating and is characterized by partial austenitization of kamacite with taenite filling between residual kamacite grains. Acicular plessite forms during cooling prior to reaching the α + γ region where silicate inclusions within taenite serve as intergranular nucleation sites for kamacite. Duplex plessite forms during the quenching event after shock reheating when the homogenous taenite becomes thermodynamically unstable, leading to either spinodal decomposition or nucleation and growth; meanwhile, duplex plessite is also formed through brittle fracture of kamacite. Pearlitic plessite forms upon reaching the eutectoid point where kamacite nucleates on grain boundaries and grows into surrounding taenite grains. The formation mechanism behind these four distinct forms of plessite provides valuable insights not only into the thermal evolution of L chondrites but also into other meteorites containing Fe‐Ni metal. Plain Language Summary: In this study, we analyzed the microstructure of plessite, a composite material comprised of kamacite (α) and taenite (γ), within L group chondrites using Electron Backscatter Diffraction. We investigated four distinct plessite varieties (net, acicular, duplex, and pearlitic) to uncover their formation mechanisms. Our research revealed that net plessite forms due to shock reheating, with partial transformation of kamacite into taenite, while acicular plessite develops during cooling, aided by silicate inclusions in taenite. Duplex plessite results from rapid cooling following post‐shock reheating. Pearlitic plessite forms during a slow cooling process, where kamacite nucleates along grain boundaries and grows into surrounding taenite grains. Understanding these formation mechanisms provides new insights into the metallographic cooling rate calculation of planetary bodies, which will impact our understanding of the differentiation of planetary cores, the generation of magnetic fields, and the geological evolution of planets. Key Points: Silicate inclusions within taenite provide intergranular nucleation sites for kamacite, leading to the formation of acicular plessiteThe homogenous taenite experiences either spinodal decomposition or nucleation and growth, leading to the formation of duplex plessiteTenham's cooling rate after impact event has been further constrained to 1–10℃/s
- Subjects
CHONDRITES; METAL analysis; DISCONTINUOUS precipitation; BRITTLE fractures; CRYSTAL grain boundaries; PEARLITIC steel; SIDEROPHILE elements
- Publication
Journal of Geophysical Research. Planets, 2024, Vol 129, Issue 1, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2023JE007940