Presentation Information
[PPS12-17]Formation of barred olivine chondrule textures based on driving-force-dependent crystal growth kinetics
*Hitoshi Miura1 (1.Graduate School of Science, Department of Information and Basic Science, Nagoya City University)
Keywords:
chondrule,solidification,numerical simulation
The diverse solidification textures observed in chondrules record their thermal histories and formation environments and thus provide key constraints on the evolution of solid materials in the early Solar System. However, the physical mechanisms responsible for individual textures remain poorly understood. A notable example is the barred olivine (BO) chondrule, characterized by a single olivine crystal with a rim–bar double structure, comprising a rim surrounding the chondrule margin and parallel bar-like structures in the interior. These features share an identical crystallographic orientation and are therefore inferred to have formed through a single crystal growth process.
In previous numerical simulations, we successfully reproduced crystal growth patterns analogous to the rim–bar double structure [1], but only by introducing a phenomenological assumption that crystal growth is enhanced along the surface of the chondrule melt. In this study, we present a new model, based on the physics of crystal growth, that explains rim formation without such assumptions. The central concept of the model is that the growth efficiency of crystallographic faces depends on the crystallization driving force. Olivine growth exhibits strong anisotropy, and the efficiency of specific crystal faces is significantly reduced at low driving forces but increases rapidly with increasing driving force as a result of atomic-scale roughening of the crystal surface.
By incorporating this driving-force dependence into a numerical model based on classical two-dimensional nucleation theory, we show that rim–bar double structures are reproduced only within an appropriate range of model parameters. The rim grows spontaneously along the melt surface, while parallel bar-like crystals develop in the interior, closely resembling those observed in natural BO chondrules. Rim formation is naturally explained by selective evaporation from the melt surface, which induces compositional supercooling and locally enhances the crystallization driving force. This physically grounded framework provides a new perspective on the formation mechanisms of BO chondrules.
Reference: [1] H. Miura et al., Sci. Adv. 11 (2025) eadw1187
In previous numerical simulations, we successfully reproduced crystal growth patterns analogous to the rim–bar double structure [1], but only by introducing a phenomenological assumption that crystal growth is enhanced along the surface of the chondrule melt. In this study, we present a new model, based on the physics of crystal growth, that explains rim formation without such assumptions. The central concept of the model is that the growth efficiency of crystallographic faces depends on the crystallization driving force. Olivine growth exhibits strong anisotropy, and the efficiency of specific crystal faces is significantly reduced at low driving forces but increases rapidly with increasing driving force as a result of atomic-scale roughening of the crystal surface.
By incorporating this driving-force dependence into a numerical model based on classical two-dimensional nucleation theory, we show that rim–bar double structures are reproduced only within an appropriate range of model parameters. The rim grows spontaneously along the melt surface, while parallel bar-like crystals develop in the interior, closely resembling those observed in natural BO chondrules. Rim formation is naturally explained by selective evaporation from the melt surface, which induces compositional supercooling and locally enhances the crystallization driving force. This physically grounded framework provides a new perspective on the formation mechanisms of BO chondrules.
Reference: [1] H. Miura et al., Sci. Adv. 11 (2025) eadw1187