Journal
ANNUAL REVIEW OF EARTH AND PLANETARY SCIENCES, VOL 46
Volume 46, Issue -, Pages 67-97Publisher
ANNUAL REVIEWS
DOI: 10.1146/annurev-earth-060614-105224
Keywords
fluids; lower crust; metamorphism; conductivity
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Deep fluids are important for the evolution and properties of the lower continental and arc crust in tectonically active settings. They comprise four components: H2O, nonpolar gases, salts, and rock-derived solutes. Contrasting behavior of H2O-gas and H2O-salt mixtures yields immiscibility and potential separation of phases with different chemical properties. Equilibrium thermodynamic modeling of fluid-rock interaction using simple ionic species known from shallow-crustal systems yields solutions too dilute to be consistent with experiments and resistivity surveys, especially if CO2 is added. Therefore, additional species must be present, andH(2)O-salt solutions likely explain much of the evidence for fluid action in high-pressure settings. At low salinity, H2O-rich fluids are powerful solvents for aluminosilicate rock components that are dissolved as polymerized clusters. Addition of salts changes solubility patterns, but aluminosilicate contents may remain high. Fluids with X-salt = 0.05 to 0.4 in equilibrium with model crustal rocks have bulk conductivities of 10(-1.5) to 100 S/m at porosity of 0.001. Such fluids are consistent with observed conductivity anomalies and are capable of the mass transfer seen in metamorphic rocks exhumed from the lower crust.
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