Dislocations in naturally deformed olivine: Example of a mylonitic peridotite

Abstract

We have investigated the microstructure of naturally deformed olivine (chemically equilibrated at 1000 °C) by conventional transmission electron microscopy and electron tomography. The peridotite specimen, from Oman ophiolite, has a mylonitic microstructure with remnant, strongly deformed, millimetric porphyroclasts co-existing with small newly formed olivine grains generated by dynamic recrystallization. Imaging by transmission electron microscopy reveals that both newly formed grains and porphyroclasts display [100] and [001] dislocations activity. Subgrain boundaries are composed of either [100] or [001] dislocations. The characterization of this natural sample also permits to identify sporadic [100] dislocation loops, rare [010] dislocation, infrequent melt, and intragranular bubbles or along subgrain boundaries. Electron tomography permits to identify several glide planes, which are similar to previous observations acquired on experimentally deformed polycrystalline olivine, more importantly electron tomography also permits to evidence combination of glide, climb and mixed climb (dislocation moving in an intermediate plane between the plane of glide plane and the plane of pure climb). Our study further infers the diversity of linear defects responsible for plastic deformation of olivine at lithospheric conditions.