Water Storage in Planetary Interiors: Hydrogen Incorporation in High Pressure Minerals

Event Dates: 

Wednesday, September 9, 2015 - 4:00pm

CTQM Seminar Type: 

  • Related Seminar Series

Speaker Name(s): 

Joe Smythe

Speaker Affiliation(s): 

University of Colorado Boulder

Abstract, Event Details: 

Although Earth is a water planet, and water dominates all of the surface processes, the oceans are only 0.023 % of the planet’s mass (230 ppm). Hydrogen is soluble, to greater or lesser extent, in all of the oxygen minerals of the interior. The Earth’s mantle is solid rock composed of oxygen minerals, mostly silicates, and composes two thirds of the mass of the planet.  Small amounts of H incorporated in these minerals are thus a much larger potential reservoir of water than is the ocean. Hydrogen has a unique geochemistry and usually occurs as a hydroxyl (OH) group in minerals. Its substitution in nominally anhydrous silicates is typically charge-balanced by vacancy at a divalent metal site, which reduces the density of the crystal and increases the compressibility. Hydrogen is relatively mobile in these crystals and can facilitate deformation and increase electrical conductivity. By controlling deformation, H controls viscosity and thus convection. H substitution in these minerals can decrease P-wave and S-wave seismic velocities, as well as density, and lower the temperature onset of melting by hundreds of degrees C.  ‘Water’, incorporated in minerals, may thus control many of the processes of the interior that drive plate tectonics as well the surface processes.