Connectivity of aqueous fluid in the Earth's upper mantle

The geometrical distribution of the aqueous fluid ih textural equilibrium with forsterite has been investigated by measurements of the dihedral angle, theta, at pressures of 3 and 5 GPa and at 1000 degrees C. The measured a at 3 and 5 GPa are 48 degrees and 40 degrees to 42 degrees, respectively. Since a value of theta smaller than 60 degrees indicates that the aqueous fluid can form an interconnected network along the three-grain and through the four-grain junctions, the existing aqueous fluid in the mantle can migrate by percolation even at the small volume fractions in the pressure range. Combining these results with previously published results at lower pressure, it is suggested that the interconnected network of aqueous fluid is stable only at higher pressure than 2 Cpa for the commonly accepted water content of the upper mantle. The present results show that the large scale transport of aqueous fluid is possible above 2 GPa, and that the physical properties of the upper mantle may change drastically at that pressure.