Water release and homogenization by dynamic recrystallization of quartz

Abstract

Abstract. To evaluate changes in water distribution generated by dynamic recrystallization of quartz, we performed infrared (IR) spectroscopy mapping of quartz in deformed granite from the Wariyama uplift zone in NE Japan. We analyzed three granite samples with different degrees of deformation: almost undeformed, weakly deformed, and strongly deformed. Dynamically recrystallized quartz grains with a grain size of ∼10 µm are found in these three samples, but the percentages of recrystallized grains and the recrystallization processes are different. Quartz in the almost-undeformed sample shows wavy grain boundaries, with a few bulged quartz grains. In the weakly deformed sample, bulging of quartz, which consumed adjacent host quartz grains, forms regions of a few hundred micrometers. In the strongly deformed sample, almost all quartz grains are recrystallized by subgrain rotation. IR spectra of quartz in the three samples commonly show a broad water band owing to H2O fluid at 2800–3750 cm−1, with no structural OH bands. Water contents in host quartz grains in the almost-undeformed sample are in the range of 40–1750 wt ppm, with a mean of 500±280 wt ppm H2O. On the other hand, water contents in regions of recrystallized grains, regardless of the recrystallization processes involved, are in the range of 100–510 wt ppm, with a mean of 220±70 wt ppm; these values are low and homogeneous compared with the contents in host quartz grains. These low water contents in recrystallized regions also contrast with those of up to 1540 wt ppm in adjacent host grains in the weakly deformed sample. Water contents in regions of subgrains are intermediate between those in host and recrystallized grains. These results for water distribution in quartz imply that water was released by dynamic recrystallization.