花崗岩質岩の浮きあがり,非圧縮性Newton流体とみなして
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概要
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Geological phenomena have been quantitatively studied so far by BERNER et al. (1972), DIETERICH et al. (1969) and others, who have considered a rock body to be a viscous fluid. However, the "Variational Principles" used as their theoretical basis are imperfect. Strictly speaking, these are not variational principles.In the present paper, using the exact variational principle for the incompressible Newtonian fluid, the writer analysed numerically the "rising of a granitic mass", which is one of the important phenomena at the later stage of orogenesis, by employing only the gravity as an external force. For this study, models were assumed on a vertical plane with a round mass of migmatite (density 2.76g/cm^3, viscosities 10^<21> poises and 10^<20> poises) 8km in diameter, located in the crust (density 3.04g/cm^3, viscosity 10^<22> poises) 10km below the ground surface (free surface). So the migmatite mass should move upward according to its buoyant force.The results of the analysis using the models are concluded as follows: (1) The centre of the migmatite mass rises initially at the rate of 0.5-0.7mm/year, and thereafter the rate gradually decreases with the progress of the rise until it finally becomes zero when the centre reached the depth of approximately 3km. (2) The amount of the rise of the earth's surface is 100-150m in maximum. (3) The viscosity of a buoyant mass does not concern with the rate of the rising of a buoyant mass, but it affects the shape of the lower half of the mass. (4) The value of deviation stresses ranges from several to several tens of bars throughout the region in question, and the corresponding strain rates are 10^<-12>-10^<-16> sec^<1->.It is apparent from the above results, especially the second one, that some other factors than gravity must be considered for the mountain-building process, otherwise the formation of mountains as high as several kilometers cannot be expected as the later stage of orogenesis.
- 日本地質学会の論文
- 1975-12-15