The effect of water on the high-pressure phase boundaries in the system Mg2SiO4-Fe2SiO4

Abstract

The phase boundaries between olivine, wadsleyite and ringwoodite have been studied comparatively under anhydrous and hydrous conditions with a fixed H 2O content of 1 wt% at 1673K. By comparing anhydrous and hydrous samples from the same experimental runs, we determined that two-phase coexisting loop in the olivine-wadsleyite boundary shifted towards lower pressure or lower iron content by the effect of H2O, which is consistent with our previous work [1]. On the other hand, the loop in the wadsleyite-ringwoodite boundary shifted towards higher pressure or higher iron content, and the pressure width of the loop decreased. Thus, the presence of H2O in the Earth's mantle will sharpen the 520-km seismic discontinuity, deep the depth of the discontinuity. © 2010 IOP Publishing Ltd.