DI13B-2671
Equation of state and elasticity of the 3.65 Å phase- constraining mantle hydration from the seismic X-discontinuity
Monday, 14 December 2015
Poster Hall (Moscone South)
Mainak Mookherjee1, Sergio Speziale2, Hauke Marquardt3, Sandro Jahn2, Bernd Wunder4, Monika Koch-Müller2 and Hans-Peter Liermann5, (1)Cornell University, Ithaca, NY, United States, (2)Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany, (3)Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, Germany, (4)Helmholtz-Zentrum Potsdam GFZ, Potsdam, Germany, (5)DESY, HASYLAB, PETRA III, P02, Hamburg, Germany
Abstract:
The 3.65 Å phase [MgSi(OH)6] is potentially a major carrier of water into the Earth’s interior. It is formed at pressures of 9-10 GPa, which correspond to a depth of 270-330 km. In this study, we use a combination of X‐ray diffraction and first principles simulations to constrain the equation of state and elasticity of the 3.65 Å phase. We find that the density of the 3.65 Å phase is slightly lower than the density of the 10 Å phase, which is stable at conditions relevant to cold subduction zones. However, the bulk sound velocities of the 3.65 Å phase are faster compared to the 10 Å phase. An assemblage of dense mantle phases such as stishovite (st), high-pressure clinoenstatite (HPCen) in association with the 3.65 Å phase (~8 %) could account for the seismically observed X-discontinuity. Based on the observed seismic reflection coefficient, we predict that the water content in cold subduction zone settings as in Tonga could be as high as 3 wt%.
