Cataclastic flow of feldspar: an experimental study

The authors have experimentally investigated cataclastic flow of albite aggregates, as well as the transition with increasing T to dislocation creep. Cataclastic flow has been observed in samples deformed at 500 to 900/sup 0/C at 5 and 10 kb, and 500 to 800..pi..C at 15 kb, at a element of of 10/sup -6//sec; the transition to recrystallization-accommodated dislocation creep is relatively sharp, and occurs at approx.900/sup 0/C at 10 kb and approx.800/sup 0/C at 15 kb. The optical textures of feldspar aggregates deformed in the cataclastic flow and dislocation creep regimes might easily be mistaken for one another. Samples deformed by cataclastic flow show original grains which are progressively and quite homogeneously flattened with increasing strain, with patchy undulatory extinction and multiple sets of roughly planar zones of different extinction; although there are occasional visible offsets on discrete grain-scale faults, there are few optically identifiable crust products. In contrast, samples deformed by dislocation creep show unflattened original grains surrounded by very fine, equant grains; the original grains become rounded and reduced in size with increasing strain. TEM of samples deformed by cataclastic flow show that micro-crush and shear zones initiate on cleavages; subsidiary cross fractures generate fragments which then rotate.more » A large proportion of some grains is reduced to fragments less than 0.01 ..mu..m in diameter. TEM of samples deformed by dislocation creep shows that the original grains have a high density of immobile dislocations and the fine grains are generated by recrystallization due to grain boundary migration.« less