Analysis of dynamic recrystallization and nucleation in a quartzite mylonite

Electron backscatter diffraction (EBSD) has been used to analyse a natural quartz mylonite from the Stack of Glencoul, NW Scotland. This technique has been used to measure the misorientation between original protolith ‘parent’ grains and recrystallized ‘daughter’ grains. The angle of misorientation is important because it has implications for the controlling recrystallization mechanism. The sample exhibits approximately 65% a recrystallized microstructure. The average neighbor-daughter grain size is 12 μm and the average subgrain size of the parent grain is 16 μm. The parent grains do not show a systematic increase in misorientation from the centre of the grain to the edges. These data are inconsistent with the subgrain rotation recrystallization model. We propose that recrystallization was facilitated by bulging during strain-induced grain boundary migration. However, the majority of misorientations between the parents and their neighbouring daughter grains are in the range 10–30° requiring that another process has operated to rotate grains to higher misorientations with respect to their parents. This process is likely to be grain boundary sliding.