Deformation of chlorite in naturally deformed low-grade rocks

Abstract

The intracrystalline deformation of chlorite in naturally deformed low-grade rocks was investigated with transmission electron microscopy (TEM). As in other phyllosilicates, the deformation of chlorite is dominated by the (001) slip plane. Slip along this plane is very easy through the generation and movement of (partial) dislocations with Burgers vector b = 1/n[uv0]. After initial bending of the (001) planes through a flexural slip mechanism, accommodated by slip along (001), the misorientation is concentrated in tiltwalls subnormal to (001), which are formed by (partial) dislocations with b = 1/n[uv0]. Tiltwalls subparallel to (001) are formed by arrays of dislocations with a total Burgers vector [001]. These boundaries are either initiated at the grain boundary and move inwards by dislocation climb, or form by movement of free dislocations towards the tip of propagating boundaries by glide along planes inclined to (001); once a boundary is formed, the increasing misfit is accommodated by climb of these dislocations along (001). Due to the combination of very easy slip along (001) and the ability to form subgrain boundaries subparallel to (001) by dislocation climb and activation of hard slip systems, chlorite deforms plastically even at temperatures below 300°C.