A new hydrous silicate, a water reservoir, in the upper part of the lower mantle

Eiji Ohtani, Hiroki Mizobata, Yasuhiro Kudoh, Toshiro Nagase,
Haruo Arashi, Hisayoshi Yurimoto, Isoji Miyagi

Geophysical Research Letters
Vol. 24, No. 9, 1047-1050, (1997)

Abstract:

  We synthesized a new hydrous silicate in the pressure range from 20
GPa to 24 GPa at 800-1300 deg-C. This phase, named tentatively as
phase G, has a hexagonal unit cell, a=4.790(3)A and c=4.344(3)A, and
V=86.3(2)A^3 and the atomic ratio Mg/Si=0.66 +- 0.03. SIMS analysis
revealed that it contains 14.5 +- 2.0 wt% water. Phase G has a
chemical formula of Mg1.14 Si1.73 H2.81 O6 and a density of 3.37
g/cm^3. Phase G coexists with periclase and Mg-perovskite under the
lower mantle conditions, and thus it can be a reservoir of water in
cold slabs penetrating into the lower mantle.