Hydrogen incorporation in upper mantle minerals

Henrik Skogby

Many of the nominally anhydrous rockforming minerals have been shown to contain low but significant concentrations of hydrogen, structurally bound as hydroxyl ions. With the development of analytical methods that can discriminate the structurally incorporated hydrogen from adsorbed water, fluid inclusions and hydrogen bound in included minerals, a more complete picture of the role of hydrogen in these phases has evolved. The hydrogen concentration for a specific mineral is normally correlated with the geological occurrence.

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Hydrogen in upper mantle minerals (olivine, ortho-and clinopyroxene, garnet) are of specific interest since they provide a mantle-water storage mechanism. Concentrations over 1000 wt ppm H2O for pyroxenes and 100 wt ppm H2O for olivine and garnet have been measured. In total, the amount of water stored in these phases seems to correspond to the amount being present in the hydrosphere.

In this project, experimental and analytical studies are performed to achieve more information regarding hydrogen incorporation in mantle minerals. The hydrogen exchange mechanisms are investigated and the difference in reaction kinetics for iron-containing and synthetic iron-free samples is studied by spectroscopic methods. The main analytical method being used is FTIR spectroscopy. The project also involves participation in further development of nuclear micro-analysis methods being conducted at the Lund Institute of Technology. The project is part of an EU-funded research training network (HYDROSPEC).

Network homepage: http://www.omp.obs-mip.fr/omp/umr5563/4equ/min/ingrin/europe/HomeNetpage.htm

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