QUARTZ DEFORMATION IN A VERY FINE-GRAINED QUARTZO-FELDSPATHIC MYLONITE - A LACK OF EVIDENCE FOR DOMINANT GRAIN-BOUNDARY SLIDING DEFORMATION

Microstructural and microtextural investigations by transmission electron microscopy (TEM) have been performed on very fine grained quartzo-feldspathic mylonites from the Red Bank Deformed Zone, Central Australia. The study of the quartz reveals a mean grain size (2.3 +/- 0.8 mu m) and microstructural features indicative of dislocation creep processes within the very fine grained quartz. Analysis of local crystallographic preferred orientation (CPO) by TEM, showed a strong CPO for both the c- and a-axes. The crystallographic relationships between adjacent grains and subgrains are consistent with dominant [c + a] and [a] slip. Microstructural and microtextural studies also show that the recrystallization mechanism included local grain boundary migration and the formation of high angle grain boundaries from low angle (sub)grain boundaries by Progressive misorientation. We found no abnormal grain rotations as would be expected to result from grain boundary sliding processes. This suggests that grain boundary sliding was not significant and the dominant deformation mechanism was dislocation creep.