HR: 0800h
AN: T11B-1254    [Abstracts]
TI: Grain boundary wetness of texturally equilibrated rocks with implications for the seismic properties of the upper mantle
AU: * Yoshino, T
EM: yoshta@rpi.edu
AF: Rensselaer Polytechnic Institute, 110 8th St., Troy, NY 12180 United States
AU: Takei, Y
EM: ytakei@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-0032 Japan
AU: Wark, D A
EM: warkd@rpi.edu
AF: Rensselaer Polytechnic Institute, 110 8th St., Troy, NY 12180 United States
AU: Watson, E B
EM: watsoe@rpi.edu
AF: Rensselaer Polytechnic Institute, 110 8th St., Troy, NY 12180 United States
AB: Melt- or fluid-filled pore geometry in the texturally equilibrated aggregates was investigated quantitatively by measuring the grain-boundary wetness, which is defined by the ratio of solid-liquid boundary area over the total area of interphase boundaries. The merit to measure the wetness is that, being combined with the granular model, the bulk mechnical properties of the liquid-bearing aggregates can be predicted quantitatively. Especially, detailed study on the wetness of the partially molten peridotite was performed to clarify the characteristics of the seismic low velocity zones in the upper mantle. The measurments were performed on several systems characterized by various dihedral angles and degree of faceting. The result shows that the grain boundary wetness increases monotonically with increasing liquid volume fraction. For no faceting system and olivine-basalt system with low dihedral angle, the relation between liquid volume fraction (f) and the wetness (y) is quite consistent with the theoretical prediction from the dodecakeidecahedral packing geometry. On the other hand, the wetness obtained for the systems showing strong faceting is generally lower than the theoretical prediction. Partially molten lherzolite shows systematically lower wetness than the simple olivine-basalt system. For all systems the obtained wetness-liquid volume fraction relationship can be fitted well to formulae $\psi=A\phi^{1/2}$ with fitting parameter A, independently of degree of faceting and dihedral angles. This suggests that the 3 dimensional pore shape is not a disk shape but a tubular one. The values of A ranges from 1.4-2.5 (A=2.3 for the olivine-basalt system and A=1.7 for the partially molten lherzolite). The seismic wave velocities of the systems whose pore geometry is characterized by parameter A can be represented by the equivalent aspect ratio of the oblate spheroid model. A=1.4-2.5 corresponds the equivalent aspect ratio of 0.25-0.09. The equivalent aspect ratios of the olivine-basalt system and the partially molten lherzolite are obtained as 0.1 and 0.15, respectively. The result indicates that the dlnVs/dlnVp expected for the partially molten peridotite in textural equilibrium is 1-1.5, which is much smaller than the value ($\sim$ 2) expected for the thin cracks and dikes. The present results agree with the previous results on the basis of isotropic model. The effect of facetting on the seismic wave velocities is not significant in the partially molten peridotite. These results would allow more accurate prediction of liquid content in texturally equilibrated rocks using Vp (or Vs) data and also more realistic interpretation of the pore geometry determined from the combined analysis of Vp and Vs data.
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 5102 Acoustic properties
DE: 5112 Microstructure
DE: 7218 Lithosphere and upper mantle
DE: 3630 Experimental mineralogy and petrology
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting