TY - JOUR
T1 - Effects of the Fe3+ spin transition on the properties of aluminous perovskite-New insights for lower-mantle seismic heterogeneities
AU - Catalli, Krystle
AU - Shim, Sang Heon
AU - Dera, Przemyslaw
AU - Prakapenka, Vitali B.
AU - Zhao, Jiyong
AU - Sturhahn, Wolfgang
AU - Chow, Paul
AU - Xiao, Yuming
AU - Cynn, Hyunchae
AU - Evans, William J.
N1 - Funding Information:
We thank three anonymous reviewers for helpful comments that improved the manuscript. Use of GSECARS was supported by the NSF ( EAR-0622171 ) and DOE ( DE-FG02-94ER14466 ). Use of Sector 3 was partially supported by COMPRES . Portions of this work were performed under the auspices of the DOE by the Univ. of Calif., Lawrence Livermore National Lab (W-7405-Eng-48). Use of HPCAT was supported by DOE-BES , DOE-NNSA , NSF , DOD-TACOM , and the W.M. Keck Foundation . Use of the APS was supported by the DOE ( DE-AC02-06CH11357 ). K.C. is supported by the DOE NNSA Stewardship Science Graduate Fellowship. This work is supported by NSF to S.H.S. ( EAR0968685 ).
PY - 2011/10/15
Y1 - 2011/10/15
N2 - We have measured the effects of the coupled substitution of Fe3+ and Al on the density and compressibility of mantle silicate perovskite (Pv) up to 95GPa. X-ray emission spectroscopy and synchrotron Mössbauer spectroscopy reveal a rapid increase in the population of low-spin Fe3+ in Fe3+, Al-bearing Pv over a narrow pressure range near 70GPa, which is in sharp contrast with Al-free Fe3+-bearing Pv, where Fe3+ undergoes a gradual spin transition, and with Al-free Fe2+-bearing Pv, where Fe2+ does not become low spin. At low pressure, Fe3+ and Al expand the perovskite lattice. However, near the pressure range of the abrupt increase in the low-spin population, the unit-cell volume of Fe3+, Al-bearing Pv becomes similar to that of Mg-endmember Pv, while those of Al-free Fe3+-bearing Pv and Al-free Fe2+-bearing Pv remain larger throughout the lower mantle. Consequently, Pv in Al-rich systems should have lower density in the shallow lower mantle but similar or greater density than Pv in pyrolite in the deep lower mantle, affecting the buoyancy and mechanical stability of heterogeneities. Although the Fe3+ spin transition in Pv is unlikely to cause a seismic discontinuity at mantle temperatures, it may result in a large change in bulk sound speed at 1200-1800km depth, such that a vertically extending structure with an elevated amount of Fe3+ would generate slower and faster anomalies above and below the depth of the spin transition, respectively, relative to the surrounding mantle. This may have important implications for bulk sound speed anomalies observed at similar depths in seismic tomography studies.
AB - We have measured the effects of the coupled substitution of Fe3+ and Al on the density and compressibility of mantle silicate perovskite (Pv) up to 95GPa. X-ray emission spectroscopy and synchrotron Mössbauer spectroscopy reveal a rapid increase in the population of low-spin Fe3+ in Fe3+, Al-bearing Pv over a narrow pressure range near 70GPa, which is in sharp contrast with Al-free Fe3+-bearing Pv, where Fe3+ undergoes a gradual spin transition, and with Al-free Fe2+-bearing Pv, where Fe2+ does not become low spin. At low pressure, Fe3+ and Al expand the perovskite lattice. However, near the pressure range of the abrupt increase in the low-spin population, the unit-cell volume of Fe3+, Al-bearing Pv becomes similar to that of Mg-endmember Pv, while those of Al-free Fe3+-bearing Pv and Al-free Fe2+-bearing Pv remain larger throughout the lower mantle. Consequently, Pv in Al-rich systems should have lower density in the shallow lower mantle but similar or greater density than Pv in pyrolite in the deep lower mantle, affecting the buoyancy and mechanical stability of heterogeneities. Although the Fe3+ spin transition in Pv is unlikely to cause a seismic discontinuity at mantle temperatures, it may result in a large change in bulk sound speed at 1200-1800km depth, such that a vertically extending structure with an elevated amount of Fe3+ would generate slower and faster anomalies above and below the depth of the spin transition, respectively, relative to the surrounding mantle. This may have important implications for bulk sound speed anomalies observed at similar depths in seismic tomography studies.
KW - Aluminum
KW - Ferric iron
KW - Heterogeneities
KW - Perovskite
KW - Spin transition
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U2 - 10.1016/j.epsl.2011.08.018
DO - 10.1016/j.epsl.2011.08.018
M3 - Article
AN - SCOPUS:80053380171
SN - 0012-821X
VL - 310
SP - 293
EP - 302
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 3-4
ER -