Fig. 6.

Photomicrographs under crossed polars. Sample numbers refer to the Harker Collection catalogue, Sedgwick Museum, University of Cambridge. a Domenigoni granodiorite, Domenigoni Valley, S. California batholith. Euhedral plagioclase grains (plag) exhibiting concentric composition growth zoning are cemented by quartz (qtz) with undulose extinction. The plagioclase shows no signs of dislocation creep. Sample 58224. Scale bar is 1 mm long. b Hornblende-biotite-tonalite, Yosemite National Park (near Tiaga Pass). This rock comprises a well-formed framework of euhedral facetted plagioclase grains, cemented by interstitial quartz. The only sign of dislocation creep is the undulose extinction in the quartz. Sample 71511. Scale bar is 1 mm long. c Close-up of a region of b, demonstrating the undulose extinction in the quartz, while the zoned plagioclase bounding the interstitial quartz has no sign of dislocation creep and a well-defined facetted growth surface. Sample 71511. Scale bar is 200 mm long. d Domenigoni granodiorite, Domenigoni Valley, S. California batholith. Note the extensively developed fine-grained regions in the interstitial quartz, indicative of dynamic recrystallization during dislocation creep. Recrystallization is particularly concentrated at boundaries with the (undeformed) plagioclase. Sample 58224. Scale bar is 1 mm long