Current Research Activities

CURRENT RESEARCH ACTIVITIES

Investigation of silicate-water interaction in hydrous silicate melt systems

The hydrothermal diamond-anvil cell offers an optical window for in-situ spectroscopic investigations of silicate melts and hydrous fluids at high temperature and pressure. These data are needed to examine structural interaction between H2O and silicate melts and solution mechanisms of silicate in aqueous solutions under crustal and upper mantle pressure and temperature conditions. Coupled with determination of solubility of H2O in melts and the solubility of silicate in hydrous fluids (with and without other salts), a complete structural description of melt-water systems will be obtained.

Spectral measurements of coexisting silicate melts and aqueous fluids in-situ at high pressure and temperature

The purpose of this preliminary study was development of the cell for the purpose of in-situ structural characterization of amorphous materials relevant to magmatic and metasomatic processes, coupled with suitable pressure calibration means. This study already has demonstrated that inferences based on quenched materials are unreliable in the extreme. For the first time, silicate speciation in fluids was determined, consistent with highly polymerized entities of Q3 type stoichiometry. In the melts, H+ associates with nonbridging oxygen in isolated SiO4 tetrahedra, whereas alkali metals are associated with more polymerized materials. These effects are non-quenchable. These preliminary data serve as a basis to examine the relationships between H2O, alkali, alkaline earths and alumina under crustal and upper mantle conditions.

Methods used for solubility measurements (phase equilibria, see left panel) and solution mechanisms of silicate in aqueous solutions. In-situ, high-temperature and high-pressure Raman spectroscopy, see right panel.

Inserts show view of experimental charges (quenched material in left panel and view through diamond cell in right panel).

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Oxygen isotope fractionation during high-temperature evaporation of silicates at high vacuum with and without hydrogen

Although stable isotope anomalies in the early solar nebula often has been ascribed to the presence of extra solar system component, extensive isotope fraction can also be accomplished during fractional evaporation during high-temperature events. The extent of fractionation is a complex function of diffusion control in the solids (and hence temperature and duration of the event) and extent of evaporation. These issues are addressed experimentally through experiments with crystalline silicates and through development of algorithms needed to describe the competing processes.

Comparison of experimental data (Davis et al., 1990) (data points) with model calculations for diffusion-limited kinetic isotope fractionation (curves). Values of a and b used to generate the curves are indicated.

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The role of H2O in Martian magmatic systems

The water content of the interior of Mars is estimated by employing analyzed water contents of kaersutite inclusions from SNC meteorites in conjunction with an experimentally-derived crystal-chemical model of kaersutite amphibole. The H2O contents of the magma from which the kaersutites in SNC meteorites could have crystallized is in the 100-1000 ppm range. That H2O content leads to an estimated water content of 1-35 ppm for a Martian mantle that could have been the source rock for such magmas.

H2O of Martian mantle at 1000°C as a function of pressure of kaersutite crystallization in the inclusions.

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Email: mysen@gl.ciw.edu