TITLE: Disproportionation of (Mg,Fe)SiO3 into MgSiO3 perovskite and an Fe-rich
hexagonal silicate in the deep lower mantle
AUTHORS (FIRST NAME, LAST NAME): Li Zhang1, 2, Yue Meng3, Wenge Yang4, Lin
Wang4, Wendy L Mao5, Qiaoshi Charles Zeng5, Jong Seok Jeong6, Andrew J. Wagner6, K.
Andre Mkhoyan6, Wenjun Liu7, Ruqing Xu7, Ho-kwang Mao1, 2
INSTITUTIONS (ALL): 1. Geophysical Laboratory, Carnegie Institution of Washington,
Washington, DC, United States.
2. Center for High Pressure Science and Technology Advanced Research, Shanghai, China.
3. High Pressure Collaborative Access Team, Carnegie Institution of Washington, Argonne,
IL, United States.
4. High Pressure Synergetic Consortium, Carnegie Institution of Washington, Argonne, IL,
United States.
5. Geological and Environmental Sciences, Stanford University, Stanford, CA, United
States.
6. Department of Chemical Engineering and Materials Science, University of Minnesota,
Minneapolis, MN, United States.
7. Advanced Photon Source, Argonne National Laboratory, Argonne, IL, United States.
ABSTRACT BODY: Models of the Earth’s deep interior have been built upon the basic
assumption that the lower mantle down to the top of the D″ layer mainly consists of
orthorhombic perovskite (pv) with nominally 10 mol% Fe. Using a laser-heated diamond
anvil cell, our experiments at pressures of 95-105 GPa and temperatures of 2200~2400 K
show that such perovskite is unstable; it loses its Fe and disproportionates into a nearly Fefree MgSiO3 pv and an Fe-rich (Mg,Fe)SiO3 phase with a previously unknown hexagonal
structure, causing a small volume reduction. Using the newly developed high-pressure
multigrain crystallography technique, we have identified 154 individual crystallites
belonging to the hexagonal phase in one experiment, each has a unique orientation matrix
with as many as 27 diffraction spots that gives identical unit-cell parameters, while 130
individual crystallites of the coexisting pv phase were indexed to the known Pbnm space
group. This new mineral physics observation leads to a fresh view on geophysical,
geochemical and geodynamic paradigms for the lower mantle below 2000 kilometers depth.