Static compression of chondrodite: Implications for water in the upper mantle

We have determined the equation of state of chondrodite (2Mg2SiO4·Mg(OH,F)2), a possible water‐bearing phase in the upper mantle, to 42.3 GPa at room temperature using x‐ray diffraction through the diamond cell. The isothermal bulk modulus of chondrodite, determined using the Birch‐Murnaghan equation of state, is 136.2 GPa with a pressure derivative of 3.7. Using our results, we have constructed density models for hydrous upper mantle compositions. These models indicate that up to 2 weight percent water could be present in a pyrolitic mantle, and be undetectable using seismically‐determined density constraints. We have also investigated the stability of chondrodite under lower mantle pressure and temperature conditions using the laser‐heated diamond cell. From in‐situ x‐ray diffraction at high pressure, and x‐ray diffraction and infrared reflectance and absorption spectra of quenched run products, we conclude that chondrodite breaks down to MgSiO3 perovskite, MgO and a hydrated melt at lower mantle pressures and temperatures.