Isostatic rebound and power-law flow in the asthenosphere
Laboratory experiments indicate that the asthenosphere probably deforms as a power-law fluid. The experimental flow law for high-temperature peridotite and olivine is Cė 1/ n = σ where e is strain-rate, σ deviatoric stress, n the power (observed to be about 3), and C a proportionality constant which...
| Published in: | Geophysical Journal International |
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| Main Author: | |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
1977
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| Online Access: | http://gji.oxfordjournals.org/cgi/content/short/50/3/723 https://doi.org/10.1111/j.1365-246X.1977.tb01343.x |
| Summary: | Laboratory experiments indicate that the asthenosphere probably deforms as a power-law fluid. The experimental flow law for high-temperature peridotite and olivine is Cė 1/ n = σ where e is strain-rate, σ deviatoric stress, n the power (observed to be about 3), and C a proportionality constant which is a function of composition, temperature, and confining pressure. However, most theoretical treatments of isostatic rebound have assumed that the asthensophere deforms as a Newtonian fluid. In this paper, numerical solutions are found for the relaxation of a sinusoidal surface deflection above a power-law medium. These solutions are applied to an analysis of isostatic rebound data. First, following Post & Griggs (1973), it is shown by dimensional analysis that the rate of maximum uplift of a surface depression should be proportional to the maximum amount of remaining depression raised to the power n , where n is the power of the flow law. The rebound data from Fennoscandia and Canada yield in-situ estimates of n between 2 and 4, in good agreement with the experimental results. Second, using the finite-difference method, the proportionality constant is determined which relates the rate of uplift to the amount of remaining depression. Using this constant and assuming n = 3, the rebound data from Fennoscandia, Canada, and Lake Bonneville yield in-situ estimates of about 1010 Ns1/3 m-2 for the creep coefficient C in the flow law. This is consistent with laboratory measurements for the creep of dry olivine at 1200°C. However, all three rebound areas give different values for C . Reasonable lateral temperature and compositional differences in the asthenosphere can explain the observed variations, but it is noticed that the estimates of C increase with increasing width of the rebound area. This suggests that the value of C increases with depth in the asthenosphere. Two models of increase of C with depth are examined and it is found that both can explain the rebound data without invoking lateral variations in the ... |
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