Analysis of rock microtectonics and anisotropy

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H_2O-fluid distributions in rocks critically control rock textures and microtectonics. We have shown that physical properties of fluid-bearing rocks can be estimated from the properties of mineral-fluid systems. The properties of the crust and the upper mantle are, therefore, estimated from the properties of quarts-feldspar-fluid, pyroxene-amphibole-fluid, and olivine-pyroxene-fluid systems. Here fluid is either H_2O or partial melt.In the Japan subduction zone, H_2O or partial melt causes low velocity in the crust and the upper mantle : Elasticity data of crustal and mantle minerals and of H_2O and silicate melts have been determined at high pressures and temperatures. Those data can be used to estimate elastic-wave velocities of fluid-bearing crust and mantle rocks.P-wave to S-wave velocity ratios, Vp/Vs, of mineral-melt systems are higher than those of mineral-H_2O systems. This is because the bulk modulus of silicate melt is about an order of magnitude larger than that of H_2O. Seismic tomographic studies have shown that Vp/Vs is generally high in the upper mantle low-velocity zone, indicating the presence of partial melt. On the other hand, Vp/Vs is low in the upper crustal low-velocity zone. We suggest that H_2O fluid causes low velocity in the upper crust.