H2O activity in concentrated NaCl solutions at high pressures and temperatures measured by the brucite-periclase equilibrium

Article Abstract:

Depression of the brucite-periclase dehydration equilibrium allows the measurement of H2O activities in concentrated NaCl solutions for pressures from 2 to 15 kbar and temperatures between 600 and 900 degrees celsius. The data yield a linear expression for the standard Gibbs free energy of the brucite dehydration reaction. Redetermination of the brucite-periclase equilibrium helps to inhibit back-reaction in quenching. Experimentally derived temperature-composition points in the system NaCl-H2O compare well with liquidus curves obtained from differential thermal analysis.

Chemical equilibrium, Geothermal brines

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A comparative fluid inclusion study of the Waterville and Sangerville (Vassalboro) Formations, south-central Maine

Article Abstract:

A comparative assessment of metasedimentary rocks in Waterville and Sangerville, MA, reveals the prominent carbonic fluid presence in the rocks in both locations. Rocks in the former location have maximum CO2 content in comparison to the latter location's rocks, which mostly contain CH4 and H2O. The degree of salinity in the Sangerville Formation is thrice as intense as that in Waterville. A wide variety of fluids in rocks in both regions clarify that magmatic and metamorphic fluids could not have been mixed and homogenized.

Analysis, Maine, Natural history, Fluids, Rocks, Sedimentary, Sedimentary rocks

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Formation and destruction of periclase by fluid flow in two contact aureoles

Article Abstract:

The reaction dolomite = periclase + calcite + CO2, formed periclase in steeply dipping marbles from the Beinn an Dubhaich aureole, Scotland and the Silver Star aureole, Montana. The reaction was infiltration-driven according to transport theory. Super18O-depletion fronts moved at different velocities to periclase reaction along the flow path. Brucite, the hydrated equivalent of periclase, was preserved in the high Mg/Ca layers, and the geometry of brucite marbles at Silver Star reflects the siting of high Mg/Ca beds.

Environmental aspects, Observations, Mineralogical research, Fluid dynamics

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