Modeling Deformation and Recrystalization Shear Textures in Olivine

Abstract

Low-symmetry rock materials subject to simple shear have stable texture components characterized by pole figures showing a girdle aligned parallel to the macroscopic shear or lineation direction. Microscopic observations in olivine polycrystals indicate that the majority of the crystals in those stable orientations are highly elongated and posses rather high dislocation densities, suggesting that neither recrystallization nor grain growth alone have been the dominant phenomenon. To understand the link between active slip systems and texture development we use a self-consistent tangent polycrystal plasticity theory in conjunction with a deformation-based recrystallization model that balances nucleation and growth. An ‘ad hoc’ grain-to-grain interaction scheme is incorporated to take into account the short range interaction and high mechanical heterogeneities between grains as a consequence of olivine having only three easy slip systems: (010)[100], (001)[100], and (010)[001]. The proposed model couples pairs of neighbor crystals, where their plastic spins are taken as an average of the individual ones. That results in a nonlocal evolution equation, introducing continuity of the lattice rotation field, as a constraint at the grain boundary interface. In this first approach, the selection of crystal pairs is random and leaving uncoupled the mechanical response. In particular, the proposed model correctly predicts the asymptotical evolution of texture orientations towards a constant orientation parallel to the shear plane and smaller growth intensity. Soft orientations with large strain energy will grow preferentially, while hard orientations accumulate dislocations. The effect of the lattice rotation field continuity induces less severe Lattice Preferred Orientations (LPO), which is in better agreement with the experimental observations.