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Experimental Determination of Eutectic Liquid Compositions in the MgO‐SiO 2 System to the Lowermost Mantle Pressures
Author(s) -
Ozawa Keisuke,
Anzai Miyuki,
Hirose Kei,
Sinmyo Ryosuke,
Tateno Shigehiko
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl079313
Subject(s) - eutectic system , enstatite , mantle (geology) , silicate , periclase , silicate perovskite , materials science , geology , mineralogy , crystallization , spinel , supercooling , analytical chemistry (journal) , thermodynamics , geochemistry , meteorite , chondrite , microstructure , chemical engineering , chemistry , composite material , metallurgy , astrobiology , physics , engineering , chromatography
We have performed melting experiments on the MgO‐SiO 2 binary system to 139 GPa in a diamond anvil cell. Both MgO‐MgSiO 3 and MgSiO 3 ‐SiO 2 eutectic compositions were examined by textural/chemical characterizations of recovered samples. Results demonstrate that the MgO‐MgSiO 3 eutectic becomes more enriched in MgO with increasing pressure and is close in composition to Mg 2 SiO 4 at the core‐mantle boundary (CMB) pressure. On the other hand, the MgSiO 3 ‐SiO 2 eutectic is more SiO 2 ‐rich at higher pressure and exhibits SiO 2 /(MgO + SiO 2 ) = 0.66 at the CMB. These have profound implications for a large‐scale compositional stratification possibly formed upon solidification of a magma ocean. The MgO‐MgSiO 3 eutectic liquid being more MgO‐rich than previously predicted suggests that only bridgmanite crystallizes up to 60 wt% solidification from a fully molten state of a pyrolitic lowermost mantle. In contrast, an SiO 2 layer may develop when melting/crystallization occurs in rocky objects with silica‐rich enstatite‐chondritic compositions.