title: Diamond formation in the deep lower mantle: a high-pressure reaction of MgCO3and SiO2.
abstract: Diamond is an evidence for carbon existing in the deep Earth. Some diamonds are considered to have originated at various depth ranges from the mantle transition zone to the lower mantle. These diamonds are expected to carry significant information about the deep Earth. Here, we determined the phase relations in the MgCO3-SiO2system up to 152 GPa and 3,100 K using a double sided laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction. MgCO3transforms from magnesite to the high-pressure polymorph of MgCO3, phase II, above 80 GPa. A reaction between MgCO3phase II and SiO2(CaCl2-type SiO2or seifertite) to form diamond and MgSiO3(bridgmanite or post-perovsktite) was identified in the deep lower mantle conditions. These observations suggested that the reaction of the MgCO3phase II with SiO2causes formation of super-deep diamond in cold slabs descending into the deep lower mantle.
authors.affiliation: Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan.
authors.forename: Fumiya
authors.initials: F
authors.lastname: Maeda
authors.affiliation: Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan.|V.S. Sobolev Institute of Geology and Mineralogy, SB RAS, Novosibirsk, 630090, Russia.
authors.forename: Eiji
authors.initials: E
authors.lastname: Ohtani
authors.affiliation: Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan.|Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, 980-8578, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Kamada
authors.affiliation: Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Sakamaki
authors.affiliation: Japan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5198, Japan.
authors.forename: Naohisa
authors.initials: N
authors.lastname: Hirao
authors.affiliation: Japan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5198, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ohishi