Connectivity of aqueous fluid in eclogite and its implications for fluid migration in the Earth's interior

The geometrical distribution of the aqueous fluid in textural equilibrium with eclogite was investigated by measurements of the dihedral angles at aqueous fluid-clinopyroxene-clinopyroxene (θcc , at aqueous fluid-garnet-garnet (θgg) and at aqueous fluid-clinopyroxene-garnet (θcg) triple junctions at 3-5 GPa and 700-800°C with a Kawai-type multianvil high-pressure apparatus. The dihedral angles, θcc, θgg, and θcg range from 62° to 68° and appear constant within the experimental uncertainties at the pressures and temperatures investigated. The constant dihedral angle values could be explained by the counterbalance of the effects of pressure, temperature, and the difference in Mg/(Mg + Fe) in the minerals and the aqueous fluid. The present results lead to the suggestion that the aqueous fluid in eclogite at pressures from 3 to 5 GPa (corresponding to depths of ∼90-150 km) exists as isolated pores, provided circumstances of chemical and textural equilibrium prevail. It is suggested that up to about 1-2 vol% aqueous fluid could be trapped as an interstitial fluid in eclogite and be transported to the Earth's interior at depths of at least 150 km by the subduction of the oceanic crust and by the delamination of the crustal roots.