The effect of H2O on the 410-kilometer seismic discontinuity

• Published in: Science (American Association for the Advancement of Science) Vol. 268; no. 5207; pp. 74 - 76
• Main Author: WOOD, B. J
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 07-04-1995; The American Association for the Advancement of Science
• Subjects: Computation; Earth; Earth sciences; Earth, ocean, space; Earthquakes, seismology; Exact sciences and technology; Fractions; Grade Point Average; Hydrogeology; Internal geophysics; Mantle; Mantle (Geology); Minerals; Olivine; Scientific Concepts; Seismology; Water; transformations; upper mantle; partitioning; phase transitions; seismic discontinuities; olivine; water
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.268.5207.74

The 410-kilometer seismic discontinuity is generally considered to be caused by a phase transformation of the main constituent of the upper mantle, olivine, alpha-(Mg,Fe)(2)SiO(4), to beta-(Mg,Fe)(2)SiO(4). Recent data show that H(2)O dissolves in olivine and other nominally anhydrous mantle minerals and that the partitioning of H(2)O between olivine and beta-(Mg,Fe)(2)SiO(4) is about 1:10. Such behavior strongly affects the region over which the alpha to beta phase transformation occurs and hence the seismic discontinuity that results. The observed width of the discontinuity constrains the maximum H(2)O content of upper mantle olivine to about 200 parts per million by weight.