Preface

On the Stress Dependence of Subgrain Size

“…In minerals, it cannot be assumed that the rate of misorientation increase of subgrain boundaries is very small. The phenomenon of"subgrain rotation" was first observed in quartz by Hobbs (1968), and has since been widely documented for many minerals (White, 1973;Poirier and Nicolas, 1975;Bell and Etheridge, 1976;Guillope and Poirier, 1979;Etheridge and Kirby, 1982) as an important mechanism of dynamic recrystallization. If we assume as a preliminary simplification that the degree of misorientation is linearly dependent on the strain, then we have 0 tp 36where tp is a constant.…”

Dynamic Recrystallization in a Naturally Deformed Albite

“…We therefore suggest that continued deformation of the recrystallized aggregate could have taken place by dislocation flow within individual grains, and that the existing grain boundaries were sufficiently efficient sinks for mobile dislocations and sub-boundaries to remove the need for further rccrystallization. Grain boundary migration took place but only where required to retain approximately equiaxed grainshapes (Bell and Etheridge, 1976;Etheridge and Kirby, 1983). The absence of significant softening under some experimental conditions, especially those involving subgrain rotation may be consistent with this microstructural model (Schmid et al, 1980;Kirby and Etheridge, 1983).…”

“…These grains will continue to rotate throughout further deformation, but, since they are rotating largely in response to dislocation motion, their orientations will remain within the same fabric pattern as that oftheir deformed host grain(s). In both naturally and experimentally deformed minerals, fabric patterns of deformed original grains and their recrystallized products are generally indistinguishable (Ransom, 1971;Bell and Etheridge, 1976;Etheridge and Kirby, 1983), providing further support for this recrystallization mechanism. Any form of homogeneous nucleation, whether or not the nucleus orientation is stress-controlled (Av6 Lallement and Carter, 1970), is likely to produce orientations outside the deformed grain fabric.…”

“…The phenomenon of subgrain rotation, whereby the misorientation across sub-boundaries increases with strain until high-angle boundaries are formed, was first alluded to by Hobbs (1968), and has been widely inferred (largely from optical observations) for a number of minerals (White, 1973(White, , 1977Poirier and Nicolas, 1975;Bell and Etheridge, 1976;Schmid et al, 1980;Etheridge and Kirby, 1983). It has been concluded that dislocations enter sub-boundaries faster than they can be annihilated during straining, giving rise to progressively higher boundary misorientations.…”