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[SMP25-12] Porosity wave and mineral banding in the metamorphism
Keywords:pore wave, mineral banding, metamorphism
Metamorphic and metasomatic banding are very common in the regional and contact metamorphic rocks. Mineral bands are composed mainly of retrograde assemblages of albite, chlorite, epidote, calcite and quartz in basic schists and quartz, albite, chlorite, calcite in pelitic schists of the low grade zones, although in the medium grade zones, albite, epidote, garnet, and amphiboles are common in basic schists. In many cases, bands both pelitic and basic schists together with low grade and medium grade metamorphic rocks exhibit monomineralic to bimineralic coarse grained texture compared with matrix. Besides, there is a significant difference in crystallographic orientation in matrix and bands. For examples, tabular grains of epidote occurs commonly perpendicular to the band boundary, suggesting the geometrical growth in the bands from the band wall.
By the way, in metamorphic bands abundant pores coated by oxides and hydroxide minerals appear in the central zone of the band. Those are considered to have been fluid filling pores but not pore after dissociation of carbonates, because of common existence of druse mineral of euhedral acicular quartz. Considering the periodic and parallel distribution of these metamorphic bands, it seems that there is a layered structure of fluid filling pore distribution during the retrograde metamorphism. Besides, such pores are surely considered to be the paths of metamorphic fluid. The pores in these bands also are thought to be derived from dissolution of constituent minerals.
In this paper, the author would like to proposes a theoretical model of banding distribution of the fluid filling pores during the metamorphism and metasomatism. It suggests that the banding distribution of these pores in the metamorphic rocks may result in the strain instability forming shear localization and large scale faults in the plate boundary metamorphic rocks.
By the way, in metamorphic bands abundant pores coated by oxides and hydroxide minerals appear in the central zone of the band. Those are considered to have been fluid filling pores but not pore after dissociation of carbonates, because of common existence of druse mineral of euhedral acicular quartz. Considering the periodic and parallel distribution of these metamorphic bands, it seems that there is a layered structure of fluid filling pore distribution during the retrograde metamorphism. Besides, such pores are surely considered to be the paths of metamorphic fluid. The pores in these bands also are thought to be derived from dissolution of constituent minerals.
In this paper, the author would like to proposes a theoretical model of banding distribution of the fluid filling pores during the metamorphism and metasomatism. It suggests that the banding distribution of these pores in the metamorphic rocks may result in the strain instability forming shear localization and large scale faults in the plate boundary metamorphic rocks.