Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.t13d..02s&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #T13D-02
Mathematics
Logic
8147 Planetary Interiors (5430, 5724), 8162 Rheology: Mantle, 5120 Plasticity, Diffusion, And Creep, 6218 Jovian Satellites, 3902 Creep And Deformation
Scientific paper
To date, laboratory studies of the rheological properties of partially molten mantle rocks have reached melt fractions of 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 as large as 40%. 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 1500 to 1553 K in order to determine the influence of large amounts of melt (0.15 < φ < 0.30) on the rheological behavior of partially molten rocks in both the diffusion and dislocation creep regimes. After hot-pressing San Carlos olivine (10 to 50 μ m) plus MORB ( ˜8 μ m), the melt is homogeneously distributed between grain-size melt pockets at triple junctions and smaller pockets at two-, three- and four-grain junctions. Stress vs strain rate data from samples in the diffusion creep regime (stress exponent al{n} = 1) reveal a drop in rock viscosity of several order of magnitude between φ = 0.25 and φ = 0.30, indicative of a rheologically critical melt fraction (RCMF). The combined results from experiments in the diffusion and dislocation creep regimes indicate that the flow behavior in both creep regimes is well described by the published flow laws [e.g. al{Hirth & Kohlstedt}, 2003] with strain rate ˙ {ɛ } ∝ exp(α φ ) and α = 25 for diffusion creep or α = 30 for dislocation creep. By comparing these flow laws to published values of viscosity in models of whole-mantle or thin-asthenosphere convection on Io, we can place constraints on the likely grain size, melt fraction, and differential stress. For convection limited to a thin (10 to 100 km) asthenosphere, the published range for viscosity of 108-12 Pa s requires grain sizes on the order of 10 to 100 μ m in diffusion creep, or a differential stress of 5 to 120 MPa in dislocation creep with φ ≥ 0.25 over the temperature range 1500 to 1800 K. In contrast, for convection extending through the whole mantle, the published value for viscosity of 1017 Pa s necessitates a grain size al{d} ≃ 1 to 10 mm in diffusion creep, or differential stresses of 10-2 < σ < 1 MPa in dislocation creep over the same temperature range and melt fraction. The extremely high differential stresses or the fine grain sizes required for asthenosphere convection are unlikely in a rock with the high melt fraction expected in Io's mantle. A comparison of these values for al{d}, ˙ {ɛ } and σ to those for Earth's upper mantle with al{d} = 1 mm, ˙ {ɛ } = 10-12 s-1, and σ = 0.1 MPa suggests that whole mantle convection is most likely for Io regardless of creep regime.
Kohlstedt David L.
Scott John T.
No associations
LandOfFree
The Effect of Large Melt Fraction on the Deformation Behavior of Peridotite: Implications for the Viscosity of Io's Mantle and the Rheologically Critical Melt Fraction does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Effect of Large Melt Fraction on the Deformation Behavior of Peridotite: Implications for the Viscosity of Io's Mantle and the Rheologically Critical Melt Fraction, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Effect of Large Melt Fraction on the Deformation Behavior of Peridotite: Implications for the Viscosity of Io's Mantle and the Rheologically Critical Melt Fraction will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1455058