Mathematics – Logic
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p12b1069s&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P12B-1069
Mathematics
Logic
3902 Creep And Deformation, 5120 Plasticity, Diffusion, And Creep, 5430 Interiors (8147), 6218 Jovian Satellites, 8162 Rheology: Mantle
Scientific paper
To date, laboratory studies of partially molten mantle rocks have reached melt fractions φ ˜ 0.15, a value much smaller than thought to be appropriate for the asthenosphere of Io where the degree of partial melting may be 40% or higher. Therefore, we have performed a series of high temperature, triaxial compressive creep experiments on dry synthetic peridotites in a gas medium apparatus at a confining pressure of 300 MPa and temperatures from 1450 to 1523 K in order to understand the influence of large amounts of melt (0.15 < φ < 0.40) on the rheological behavior of partially molten rocks. Mechanical mixtures of crushed and dried San Carlos olivine (1-10 μ m) plus MORB ( ˜8 μ m) were isostatically hot pressed at 1450 K and 300 MPa for 4 h. Microstructural analysis indicates that after hot pressing the melt is homogeneously distributed between grain-size melt pockets at triple junctions and smaller pockets at two, three and four grain junctions. Analysis of stress vs. strain rate data from a sample containing φ = 0.23 +/- 0.04 MORB with a grain size {d} = 9.3 +/- 2.3 μ m deformed at 1450 K and differential stresses of 10 to 75 MPa in the diffusional creep regime (stress exponent {n} = 1) demonstrates that the viscosity may be as much as three orders of magnitude higher than that predicted by a flow law reported for peridotites, where viscosity η ~ exp(-25 φ ). For example, diffusional creep data from the sample with φ = 0.23 scaled to a grain size of 1 mm and extrapolated to a temperature of 1900 K (a possible value in Io's interior) yields a viscosity of 3x1018 Pa s, compared to a viscosity of 2x1015 Pa s calculated from the flow law and published results from numerical models with viscosity values of 1017 Pa s for a homogeneous convecting mantle and 108 to 1012 Pa s for a thin convecting asthenosphere. Therefore, additional experiments on partially molten mantle rocks with relatively high φ are required to constrain the dynamic properties of Io's mantle.
Kohlstedt David L.
Scott Ted
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