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[SIT17-05] Transport of Re in subduction zone fluids.
The rhenium distribution and, therefore, Re/Os in the Earth's interior is heterogeneous perhaps because of Re transport by infiltrating aqueous fluids. For example, significant Re enrichments in the mantle wedge overlying subducting plates near continental margins have been reported reflecting, perhaps, Re transport from dehydrating slab material into the peridotite wedge via Re dissolved in the aqueous fluids. Such fluid infiltration also can trigger partial melting.
To characterize rhenium transport via infiltration of aqueous fluids in the Earth's interior as a function of the bulk chemical composition of the fluid source in the Earth's interior, Re solubility and solution mechanisms in aqueous fluids with and without other solutes in the fluids were determined to 900°C and about 1710 MPa in an externally-heated hydrothermal diamond anvil cell. The Re solubility varies by more than an order of magnitude in the temperature-pressure regime of the deep crust and upper mantle because of formation of Re complexes that also include chemical interaction of dissolved ReO2 with other solutes. The solubility of these complexes is, in particular, dependent on alkali or alkaline earth solutes. The electronic properties of the metal cation in metal in aqueous fluids at high temperature and pressure also affect Re solubility. Increasingly electronegative metal cation results in decreased Re solubility in aqueous fluid at the same temperature and pressure. In addition fluid density (temperature and pressure) also is correlated positively with Re solubility.
It is suggested that variable Re solubility in aqueous fluids that infiltrate the peridotite wedge above subducting plates can govern Re abundance and Re/Os abundance ratio of magma from partial melting of the peridotite wedge when triggered by ingress of such fluids. The alkali/alkaline earth ratio of the source of the released aqueous fluid affects the extent to which Re can be transported into an overlying peridotite mantle wedge. Existing experimental data for other HFSE also lead to the suggestion that their solubility in aqueous fluid varies by orders of magnitude depending on the type and abundance other fluid solutes.
To characterize rhenium transport via infiltration of aqueous fluids in the Earth's interior as a function of the bulk chemical composition of the fluid source in the Earth's interior, Re solubility and solution mechanisms in aqueous fluids with and without other solutes in the fluids were determined to 900°C and about 1710 MPa in an externally-heated hydrothermal diamond anvil cell. The Re solubility varies by more than an order of magnitude in the temperature-pressure regime of the deep crust and upper mantle because of formation of Re complexes that also include chemical interaction of dissolved ReO2 with other solutes. The solubility of these complexes is, in particular, dependent on alkali or alkaline earth solutes. The electronic properties of the metal cation in metal in aqueous fluids at high temperature and pressure also affect Re solubility. Increasingly electronegative metal cation results in decreased Re solubility in aqueous fluid at the same temperature and pressure. In addition fluid density (temperature and pressure) also is correlated positively with Re solubility.
It is suggested that variable Re solubility in aqueous fluids that infiltrate the peridotite wedge above subducting plates can govern Re abundance and Re/Os abundance ratio of magma from partial melting of the peridotite wedge when triggered by ingress of such fluids. The alkali/alkaline earth ratio of the source of the released aqueous fluid affects the extent to which Re can be transported into an overlying peridotite mantle wedge. Existing experimental data for other HFSE also lead to the suggestion that their solubility in aqueous fluid varies by orders of magnitude depending on the type and abundance other fluid solutes.