Jh. Kruhl, PRISM-PLANE AND BASAL-PLANE PARALLEL SUBGRAIN BOUNDARIES IN QUARTZ - A MICROSTRUCTURAL GEOTHERMOBAROMETER, Journal of metamorphic geology, 14(5), 1996, pp. 581-589
Empirical data on quartz subgrain patterns from various metamorphic ro
cks show that, at least up to 10 kbar in the stability field of low-qu
artz, prismatic subgrain boundaries are dominant whereas basal subgrai
n boundaries are not developed. In the high-quartz stability field, bo
th prismatic and basal subgrain boundaries occur and form typical rect
angular ('chessboard') patterns. The likely reason behind the differen
t occurrence of these subgrain patterns is that in high-quartz prismat
ic glide becomes as easy as, or probably even easier than, basal glide
. The two types of subgrain patterns can be clearly distinguished by o
ptical microscopy. Consequently, the occurrence of chessboard subgrain
patterns in quartz represents a practicable geothermobarometer. The p
ossibilities of its application are far reaching and include the speci
fication of deformation conditions at high-grade metamorphism, the rec
ognition of syntectonic intrusions and the distinction between pluton
emplacement at lower and at higher crustal levels.