Section 3

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Plastic Deformation of Quartz:
Recrystallization of Quartz with Grain Growth

Click image to enlarge (~1MB)

26. Recovery and grain growth in quartz - Quartz in this sample of deformed tonalite from the Borrego Springs mylonite zone, shows recrystallization to equant, polygonal new grains. Deformation was at middle greenschist facies. Many grains are in extinction (dark), indicating a strong lattice preferred orientation (see also images # 51 and #52). Some adjacent quartz grains of similar lattice orientation have coalesced, by a process of grain boundary migration (see also images # 40 through # 46), to form larger grains that define a weak, subhorizontal foliation.

FOV 1.5 mm, Nicols Crossed.

27. Recovery and grain growth in quartz - This sheared adamellite from the alpine Maggia Nappe, Ticino, Switzerland deformed at epidote-amphibolite facies. The recrystallized grain size and shape of quartz grains are controlled by the presence of biotite and small epidote grains aligned along planes parallel to the main foliation (here subhorizontal; see also image # 97). Where other mineral species are absent, as in left side of image, quartz grain boundaries have coalesced to form a single large grain. Quartz in the lower half of image has not coalesced, but has recrystallized into roughly equant, polygonal grains with straight grain boundaries that meet in 120° triple points. Most grain boundaries in the image center are at a high angle to foliation, typical for deformation of quartz under these temperature conditions. A strong lattice orientation across the image indicates that quartz deformed by dislocation glide. Polygonal grains and straight grain boundaries indicate that recovery involved grain boundary migration (see images #44 to #46).

FOV 3.2 mm, Nicols Crossed + Gypsum Plate.

Plastic Deformation of Quartz: Recrystallization of Quartz with Grain Growth	Click image to enlarge (~1MB)
26. Recovery and grain growth in quartz - Quartz in this sample of deformed tonalite from the Borrego Springs mylonite zone, shows recrystallization to equant, polygonal new grains. Deformation was at middle greenschist facies. Many grains are in extinction (dark), indicating a strong lattice preferred orientation (see also images # 51 and #52). Some adjacent quartz grains of similar lattice orientation have coalesced, by a process of grain boundary migration (see also images # 40 through # 46), to form larger grains that define a weak, subhorizontal foliation. FOV 1.5 mm, Nicols Crossed.
27. Recovery and grain growth in quartz - This sheared adamellite from the alpine Maggia Nappe, Ticino, Switzerland deformed at epidote-amphibolite facies. The recrystallized grain size and shape of quartz grains are controlled by the presence of biotite and small epidote grains aligned along planes parallel to the main foliation (here subhorizontal; see also image # 97). Where other mineral species are absent, as in left side of image, quartz grain boundaries have coalesced to form a single large grain. Quartz in the lower half of image has not coalesced, but has recrystallized into roughly equant, polygonal grains with straight grain boundaries that meet in 120° triple points. Most grain boundaries in the image center are at a high angle to foliation, typical for deformation of quartz under these temperature conditions. A strong lattice orientation across the image indicates that quartz deformed by dislocation glide. Polygonal grains and straight grain boundaries indicate that recovery involved grain boundary migration (see images #44 to #46). FOV 3.2 mm, Nicols Crossed + Gypsum Plate.