Progressive lattice misorientation and microstructural development in quartz veins deformed under subgreenschist conditions

Progressive microstructural changes in quartz veins which were moderately deformed under subgreenschist conditions have been investigated by observation of microstructures and crystallographic orientation analysis. The geometry of kink bands relative to the finite strain framework and systematic dispersion patterns of crystallographic orientations of subgrains and recrystallized grains suggest the dominant and subordinate operation of basal (0001)〈a〉 and 〈m〉, and ω {101̄3}〈a〉 slip systems, respectively, in the deformed quartz. Deformation of the quartz at an early stage was dominated by the formation of kink bands which rotated quickly and locked up at an inclination angle, α, of the active slip plane relative to the compression axis exceeding the optimum angle for slip (α=45°). Subsequently, polygonization and subgrain rotation recrystallization occurred first in highly strained portions, such as the inside of kink bands, and then outside of them. The sequential deformation process is reflected in the transition of the crystallographic orientation distribution from systematic to complicated (or random) dispersion patterns. Based on the fact that the subgrains and recrystallized grains are always elongated perpendicular to the bulk shortening axis, without any control of the orientation of active slip plane or kink bands, it is concluded that the polygonization and recrystallization by subgrain rotation were caused by a complete rearrangement of dislocation configuration by climbing, independent of kinking.