変成帯の脱水過程と力学プロセス [in Japanese] Dehydration and the Mechanics of Metamorphic Belts [in Japanese]
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Many sealed cracks in the subduction related metamorphic belt are found in metamorphic zones. They are filled with quartz, albite, chlorite, muscovite, and actinolite, and rarely with omphacite and hornblende, suggesting that they have been mainly formed during the exhumation stage of the metamorphic belt. The sealed cracks occur as a nearly vertical composite crack against the main shear plane defined by schistosity, and there is some shear displacement. The width and the spacing of sealed cracks show distribution patterns of lognormal and power law types. The spatial distribution of sealed cracks appears to be highly clustered in various space scales. The sealed crack density is high in low grade rocks, but is low in high grade rocks, suggesting that sealed crack density is controlled by the fracture or yield strength of rocks depending strongly on temperature.<BR>The evolution of the sealed crack-fluid flow system in an accretionary complex between the subducting slab and wedge mantle can be modeled from fluid occupying and flowing cracks with various densities. The behavior of the model system is characterized by a strong non-linear stochastic differential equation having scale- and time-invariant solutions. The index of the scale and time exponents is just two-thirds, which is comparable to the power exponents in the natural sealed crack clustered distribution patterns. These results suggest that the fluid flow in the accretionary complex is spatio-temporary intermittent and clustered. Further, the high crack density in the lower temperature zone near the wedge mantle induces convective fluid circulation reaching the sea floor and a low density near the slab with a unidirectional fluid flow due to the high temperature.
- J. Geogr.
J. Geogr. 109(4), 600-613, 2000-08-25
Tokyo Geographical Society