Plastic deformation and development of clinopyroxene lattice preferred orientations in eclogites

We use an anisotropic viscoplastic self-consistent (VPSC) model to simulate the development of omphacite lattice preferred orientations (LPOs) in response to deformation by dislocation glide. In these simulations, we consider slip systems identified either in naturally deformed omphacite or in experimentally deformed diopside. Simulated LPOs reproduce very well the characteristic omphacite LPO pattern in naturally deformed eclogites: a strong concentration of [001]-axes sub-parallel to the lineation and of (010)-poles sub-perpendicular to the foliation. These models reconcile the interpretation of omphacite LPOs in eclogites and TEM observations of naturally deformed omphacite, since they show that omphacite LPOs in naturally deformed eclogites may develop by dislocation glide on 1/2<110>(1 (1) over bar0),[001] {110} and [001](100). We also investigate the effect of the strain regime on the omphacite LPO development. The simulations show that changes in deformation regime lead to second-order variations in omphacite LPO patterns similar to those observed in eclogites, such as an asymmetry of the LPO relative to the structural frame, a stronger concentration of the [001]-axes relative to the (010)-pole concentration, or a dispersion of [001]-axes in the foliation plane. This suggest that omphacite LPO patterns may carry information on the deformation regime (simple shear, transtension...) active during the high-pressure events. (C) 2002 Elsevier Science Ltd. All right sreserved.