| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2001: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 2000: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1999: ¥2,900,000 (Direct Cost: ¥2,900,000)
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| Research Abstract |
It was investigated by optical microscope to analyze three-dimensional aspects of grain faces and intragranular crack surfaces in annealed granitic rocks and grain interiors of recrystallized quartz and strongly annealed olivine.
The statically recrystallized quartz grains in granitic mylonite, formed by the heating of the intrusive rocks, show several characteristic microstructures, such as labyrinths of irregular ridges and channels and circular depression. The results obtained may indicate that grain boundaries and intragranular cracks heal by similar processes. These quartz grains also show several microstructures associated with the grain boundary migration. Most of the recrystallized grains were formed by the strain-induced migration (bulging) of the original grain boundaries. The recrystallized grains contain much fewer fluid inclusions than the deformed ones, and the boundaries between recrystallized grains contain amoeboid shape fluid inclusions. Thus the migrating boundaries r
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esult in a change in size and distribution of the fluid inclusions, and may make the pictures even more complicated, such as "left over grains" and a cloud of fluid inclusions.
Dislocation structures in olivine from Ogi picrite basalt, Sado Island have been studied by oxidation decoration method. An optical examination shows that the dislocation structure divides olivines with or without subgrain boundaries (small angle boundary and/or small angle twist boundary) into two types. Although not all the subgrain boundaries are confined strictly to a single crystallographic plane, most of them are very near to a low-index plane. The subgrain structure undoubtedly formed by dislocation rearrangement (recovery) during a heating event following the original deformation.
Dislocations naturally decorated by magnetite have been observed optically in olivine megacrysts in scoria from Kiyotaki volcano, one of Kannabe volcano group, Hyogo Prefecture. The observed structures include loops, helicoidal dislocation lines, and structures produced by multiple cross-glide. Helicoidal dislocation lines and structures produced by multiple cross-glide also lie parallel and/or subparallel to low-index directions. Helicoidal dislocation lines are evidence of rapid cooling event, and structures produced by cross-glide indicate that olivine megacrysts are xenociysts and originally deformed ones.However, it was not observed small angle boundaries in olivine megacrysts. Less
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