Microstructural study of plastic flow of quartz

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(1) We collected many quartzose metamorphic rocks from the nine high P/T metamorphic belts in Japan. Their quartz microstructures are roughly classified into two groups: one is characterized by elongated grains with serrated grain boundaries which shows strong undulatory extinction; another is characterized by the equant-equigranular polygonal grains which shows no or only very slight undulatory extinction. The former will be correltated with the S-type microstructure and the latter with the P-type one of Masuda and Fujimura (1981). The former occurs in the Kamuikotan tectonic belt, Yamagami metamorphic rocks and some of the Sambagawa metamorphic belt, while the latter occurs in the Ryoke, the Yaeyama, the Nagasaki and some part of the Sambagawa metamorphic belt. According to Masuda and Fujimura (1981), the former is presumably developed at lower temperatures and faster strain rates than the latter. There are many complex microstructures which cannot be assigned to the former nor the e … More r. The classification of such microstructures is a future problem. (2) The high temperature and high pressure deformation apparatus, which was originall.y built at Nagoya University, was transported to Shizuoka University. After removing the synchronous motor-drive system and setting the computercontrolled stepping-motor system, we tried to perform a deformation experiment at temperature of 800゜C, confining pressure of 4 Kb (400 MPa) and strain rate of 10^<-6>/sec. The starting material of the experiment is the siliceous mylonite which has the foliation defined by the alternation of mica rich layers and quartz rich layers. The mylonite was uniaxially compressed parallel to the foliation, and during the experiment its layers were folded. (3) We proposed a new method that estimated relative palaeodifferential stress using microboudin structure of columnar mineral grains. This method is independent from other palaeopiezometric method such as newly recrystallized grainsize piezometer, subgrain size piezometer and dislocation density piezometer. Less