Seismic Anisotropy Due to Lattice Preferred Orientation of Minerals: Kinematic or Dynamic?
- Murli H. Manghnani and
- Yasuhiko Syono
Published Online: 21 MAR 2013
Copyright © 1987 by Terra Scientific Publishing Company (TERRAPUB), Tokyo.
High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto
How to Cite
Karato, S.-I. (1987) Seismic Anisotropy Due to Lattice Preferred Orientation of Minerals: Kinematic or Dynamic?, in High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto (eds M. H. Manghnani and Y. Syono), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM039p0455
- Published Online: 21 MAR 2013
- Published Print: 1 JAN 1987
Print ISBN: 9780875900667
Online ISBN: 9781118664124
- Mineralogy and Crystal Chemistry;
- Phase transformations;
- High Pressure-High Temperature Research
The lattice preferred orientation (LPO) of elastically anisotropic minerals is one of the most important anisotropic structures that causes seismic anisotropy. A question is addressed whether seismic anisotropy due to LPO is related to the kinematic framework (shear direction and shear plane) or to the dynamics of flow (orientation of stress). It is shown that the conventional kinematic interpretation of seismic anisotropy based on fabric studies of ultramafic rocks in ophiolites cannot be straightforwardly extrapolated to the deeper mantle, where dynamic recrystallization is important. When dynamic recrystallization occurs, the nature of LPO is determined by the relative importance of plastic deformation (dislocation glide), nucleation, and growth (grain boundary migration (GBM)). Based on experimental studies, a simple microstructural model of dynamically recrystallized materials is proposed. It is shown that the dominant mechanism of LPO is determined by the relative rates of plastic deformation, nucleation, and growth and depends on the conditions of recrystallization. When both nucleation and growth are easy compared to plastic deformation, the LPO will be determined by GBM and related to the stress, if the driving force for GBM reflects the instantaneous stress. When either nucleation or growth (or both) is difficult compared to deformation, the LPO will be determined by plastic deformation and related to the kinematic framework of flow. The transition conditions of the mechanisms of LPO were estimated for olivine, and the LPO mechanism maps were constructed. The results suggest that when dynamic recrystallization occurs, the stress-controlled seismic anisotropy will be formed in relatively cold mantle, while the kinematically controlled seismic anisotropy will be formed in relatively hot mantle.