TY - JOUR
T1 - Experimental evidence for silica-enriched Earth’s lower mantle with ferrous iron dominant bridgmanite
AU - Mashino, Izumi
AU - Murakami, Motohiko
AU - Miyajima, Nobuyoshi
AU - Petitgirard, Sylvain
N1 - Funding Information:
ACKNOWLEDGMENTS. We appreciate S. Ozawa and K. Marquardt for their assistance with the experiments. We also appreciate D. J. Frost, E. Ohtani, T. Katsura, M. Nakamura, T. Kakegawa, T. Kimura, A. Suzuki, T. Kuribayashi, S. Okumura, and T. Ishii for their useful discussions. This work was supported by MEXT/JSPS (Ministry of Education, Culture, Sports, Science and Technology/Japan Society for the Promotion of Science) KAKENHI Grants 22684028, 24654170, and 25247087, and Start-up fund at ETH Zürich to M.M., and MEXT/JSPS KAKENHI Grants 15J02017 and 19K21049 to I.M. This work was also supported by the JSPS Japanese-German Graduate Externship. S.P. is financed through a DFG (Deutsche Forschungsgemeinschaft) project (PE 2334/1-1). The Scios FIB and the Titan G2 TEM at BGI (Bayerisches Geoinstitut) were financed by DFG Grants INST 91/315-1 FUGG and INST 91/251-1 FUGG, respectively.
Publisher Copyright:
© 2020 National Academy of Sciences. All rights reserved.
PY - 2020/11/10
Y1 - 2020/11/10
N2 - Determination of the chemical composition of the Earth’s mantle is of prime importance to understand the evolution, dynamics, and origin of the Earth. However, there is a lack of experimental data on sound velocity of iron-bearing Bridgmanite (Brd) under relevant high-pressure conditions of the whole mantle, which prevents constraints on the mineralogical model of the lower mantle. To uncover these issues, we have conducted sound-velocity measurement of iron-bearing Brd in a diamond-anvil cell (DAC) up to 124 GPa using Brillouin scattering spectroscopy. Here we show that the sound velocities of iron-bearing Brd throughout the whole pressure range of lower mantle exhibit an apparent linear reduction with the iron content. Our data fit remarkably with the seismic structure throughout the lower mantle with Fe2+-enriched Brd, indicating that the greater part of the lower mantle could be occupied by Fe2+-enriched Brd. Our lower-mantle model shows a distinctive Si-enriched composition with Mg/Si of 1.14 relative to the upper mantle (Mg/Si = 1.25), which implies that the mantle convection has been inefficient enough to chemically homogenize the Earth’s whole mantle.
AB - Determination of the chemical composition of the Earth’s mantle is of prime importance to understand the evolution, dynamics, and origin of the Earth. However, there is a lack of experimental data on sound velocity of iron-bearing Bridgmanite (Brd) under relevant high-pressure conditions of the whole mantle, which prevents constraints on the mineralogical model of the lower mantle. To uncover these issues, we have conducted sound-velocity measurement of iron-bearing Brd in a diamond-anvil cell (DAC) up to 124 GPa using Brillouin scattering spectroscopy. Here we show that the sound velocities of iron-bearing Brd throughout the whole pressure range of lower mantle exhibit an apparent linear reduction with the iron content. Our data fit remarkably with the seismic structure throughout the lower mantle with Fe2+-enriched Brd, indicating that the greater part of the lower mantle could be occupied by Fe2+-enriched Brd. Our lower-mantle model shows a distinctive Si-enriched composition with Mg/Si of 1.14 relative to the upper mantle (Mg/Si = 1.25), which implies that the mantle convection has been inefficient enough to chemically homogenize the Earth’s whole mantle.
KW - Sound velocity
KW - high pressure
KW - iron spin-state change of bridgmanite
KW - mineralogical model of the lower mantle
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U2 - 10.1073/pnas.1917096117
DO - 10.1073/pnas.1917096117
M3 - Article
C2 - 33093206
AN - SCOPUS:85096079947
VL - 117
SP - 27899
EP - 27905
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
SN - 0027-8424
IS - 45
ER -