Compressional and shear wave velocities of Fe-bearing silicate post-perovskite in Earth’s lowermost mantle

Abstract

The bridgmanite (Bgm) to silicate post-perovskite (PPv) phase transition is believed to be the main cause for the distinct seismic features observed in the D'' layer, the lowermost region of the Earth’s mantle. However, the transition depth and elasticity of the PPv phase have been highly debated, as the chemical complexity within the D'' layer can largely affect the Bgm-PPv transition pressure and the associated velocity contrast. Experimental measurements of sound velocities for PPv with different chemical compositions under relevant lowermost-mantle conditions are essential but remain limited. In this study, we have reliably measured both compressional wave velocity (V_P), shear wave velocity (V_S), and density, for two Fe-bearing PPv compositions [(Mg_0.85Fe_0.15)SiO₃ and (Mg_0.75Fe_0.25)SiO₃] at lowermost mantle pressures using Impulsive Stimulated Light Scattering (ISS), Brillouin Light Scattering (BLS), and X-ray Diffraction (XRD) in diamond anvil cells. Our results indicate that the velocities of Fe-bearing PPv at 120 GPa can be described by the following relationships: V_S (km/s) = 7.65–2.8X_Fe and V_P (km/s) = 14.11–3.8X_Fe, where X_Fe represents mole fraction of the Fe content. The variations in the Fe content of PPv may provide one of the explanations for the seismic lateral variations observed at the Earth’s core mantle boundary. By comparing our results with the high-pressure velocities of Bgm, our velocity model suggests significant discontinuities across the Bgm-PPv transition, characterized by a reduction in both V_P and V_Φ, and an increase in V_S. These findings highlight the importance of considering the influence of chemical composition, particularly Fe content which could vary significantly at the D'' region, on the seismic properties of the PPv phase. The observed velocity contrasts across the Bgm-PPv transition may contribute to the complex seismic signatures observed in the D'' layer, underscoring the potential role of this phase transition in interpreting the seismic features of the lowermost mantle region.

Keywords

Fe-bearing post-perovskite / D" layer / Sound velocities

References

J. Asplet, J. Wookey, M. Kendall. A potential post-perovskite province in D ″beneath the Eastern Pacific: evidence from new analysis of discrepant SKS–SKKS shear-wave splitting. Geophy. J. Int., 221 (3) (2020), pp. 2075-2090

T.B. Ballaran, A. Kurnosov, K. Glazyrin, D.J. Frost, M. Merlini, M. Hanfland, R. Caracas. Effect of chemistry on the compressibility of silicate perovskite in the lower mantle. Earth Planet. Sci. Lett., 333 (2012), pp. 181-190

R. Caracas, R. Cohen. Effect of chemistry on the stability and elasticity of the perovskite and post-perovskite phases in the MgSiO3-FeSiO3-Al2O3 system and implications for the lowermost mantle. Geophy. Res. Lett., 32 (16) (2005), p. L16310

K. Catalli, S.-H. Shim, V. Prakapenka, J. Zhao, W. Sturhahn. X-ray diffraction and Mössbauer spectroscopy of Fe3+-bearing Mg-silicate post-perovskite at 128–138 GPa. Am. Mineral., 95 (2–3) (2010), pp. 418-421

J.W. Chaloner, C. Thomas, A. Rietbrock. P-and S-wave reflectors in D ″beneath southeast Asia. Geophy. J. Int., 179 (2) (2009), pp. 1080-1092

J. Chantel, D.J. Frost, C.A. McCammon, Z. Jing, Y. Wang. Acoustic velocities of pure and iron-bearing magnesium silicate perovskite measured to 25 GPa and 1200 K. Geophys. Res. Lett., 39 (2012), p. L19307

L. Cobden, I. Mosca, J. Trampert, J. Ritsema. On the likelihood of post-perovskite near the core–mantle boundary: A statistical interpretation of seismic observations. Phys. Earth Planet. Interiors, 210 (2012), pp. 21-35

L. Cobden, C. Thomas. The origin of D ″reflections: A systematic study of seismic array data sets. Geophy. J. Int., 194 (2) (2013), pp. 1091-1118

L. Cobden, C. Thomas, J. Trampert. Seismic detection of post-perovskite inside the Earth. The Earth's Heterogeneous Mantle: A Geophysical, Geodynamical, and Geochemical Perspective (2015), pp. 391-440

X. Ding, D.V. Helmberger. Modelling D ″structure beneath Central America with broadband seismic data. Phys. Earth Planet. Interiors, 101 (3) (1997), pp. 245-270

D.P. Dobson, J.P. Brodholt. Subducted banded iron formations as a source of ultralow-velocity zones at the core–mantle boundary. Nature, 434 (7031) (2005), pp. 371-374

S. Dorfman, T. Duffy. Effect of Fe-enrichment on seismic properties of perovskite and post-perovskite in the deep lower mantle. Geophy. J. Int., 197 (2) (2014), pp. 910-919

Fei, Y., Ricolleau, A., Frank, M., Mibe, K., Shen, G., Prakapenka, V., 2007. Toward an internally consistent pressure scale. Proceedings of the National Academy of Sciences 104(22), 9182-9186.

E.J. Garnero, A.K. McNamara, S.-H. Shim. Continent-sized anomalous zones with low seismic velocity at the base of Earth's mantle. Nature Geosci., 9 (7) (2016), pp. 481-489

Grocholski, B., Catalli, K., Shim, S.-H., Prakapenka, V., 2012. Mineralogical effects on the detectability of the postperovskite boundary. Proceedings of the National academy of Sciences 109(7), 2275-2279.

N. Guignot, D. Andrault, G. Morard, N. Bolfan-Casanova, M. Mezouar. Thermoelastic properties of post-perovskite phase MgSiO3 determined experimentally at core–mantle boundary P-T conditions. Earth Planet. Sci. Lett., 256 (1–2) (2007), pp. 162-168

A.R. Hutko, T. Lay, J. Revenaugh, E.J. Garnero. Anticorrelated Seismic Velocity Anomalies from Post-Perovskite in the Lowermost Mantle. Science, 320 (2008), pp. 1070-1074

T. Iitaka, K. Hirose, K. Kawamura, M. Murakami. The elasticity of the MgSiO3 post-perovskite phase in the Earth's lowermost mantle. Nature, 430 (6998) (2004), pp. 442-445

S.D. Jacobsen, H.J. Reichmann, H.A. Spetzler, S.J. Mackwell, J.R. Smyth, R.J. Angel, C.A. McCammon. Structure and elasticity of single-crystal (Mg, Fe) O and a new method of generating shear waves for gigahertz ultrasonic interferometry. J. Geophy. Res. Solid Earth, 107 (2002), p. B2037

J. Kendall, C. Nangini. Lateral variations in D“ below the Caribbean. Geophy. Res. Lett., 23 (4) (1996), pp. 399-402

J.M. Kendall, C. Nangini. Lateral variations in D″ below the Caribbean. Geophy. Res. Lett., 23 (4) (1996), pp. 399-402

T. Kito, S. Rost, C. Thomas, E.J. Garnero. New insights into the P-and S-wave velocity structure of the D ″discontinuity beneath the Cocos plate. Geophy. J. Int., 169 (2) (2007), pp. 631-645

E. Knittle, R. Jeanloz. Simulating the core-mantle boundary: An experimental study of high-pressure reactions between silicates and liquid iron. Geophy. Res. Lett., 16 (7) (1989), pp. 609-612

A. Kurnosov, H. Marquardt, D. Frost, T.B. Ballaran, L. Ziberna. Evidence for a Fe3+-rich pyrolitic lower mantle from (Al, Fe)-bearing bridgmanite elasticity data. Nature, 543 (7646) (2017), p. 543

Y. Kuwayama, K. Hirose, L. Cobden, M. Kusakabe, S. Tateno, Y. Ohishi. Post-perovskite phase transition in the pyrolitic lowermost mantle: Implications for ubiquitous occurrence of post-perovskite above CMB. Geophys. Res. Lett., 49 (1) (2022)

C. Langrand, D. Andrault, S. Durand, Z. Konôpková, N. Hilairet, C. Thomas, S. Merkel. Kinetics and detectability of the bridgmanite to post-perovskite transformation in the Earth's D ″layer. Nature Communicat., 10 (1) (2019), p. 5680

T. Lay, E. Garnero, S. Russell. Lateral variation of the D″discontinuity beneath the Cocos Plate. Geophys. Res. Lett., 31 (2004), p. L15612

T. Lay, D.V. Helmberger. A lower mantle S-wave triplication and the shear velocity structure of D ″. Geophy. J. Int., 75 (3) (1983), pp. 799-837

B. Li, J. Zhang. Pressure and temperature dependence of elastic wave velocity of MgSiO3 perovskite and the composition of the lower mantle. Phys. Earth Planet. Interiors, 151 (1–2) (2005), pp. 143-154

J. Liu, Q. Hu, D.Y. Kim, Z. Wu, W. Wang, Y. Xiao, P. Chow, Y. Meng, V.B. Prakapenka, H.-K. Mao. Hydrogen-bearing iron peroxide and the origin of ultralow-velocity zones. Nature, 551 (7681) (2017), p. 494

Z. Mao, J. Lin, C. Jacobs, H. Watson, Y. Xiao, P. Chow, E. Alp, V. Prakapenka. Electronic spin and valence states of Fe in CaIrO3-type silicate post-perovskite in the Earth's lowermost mantle. Geophy. Res. Lett., 37 (2010), p. L22304

Z. Mao, J.-F. Lin, J. Yang, J. Wu, H.C. Watson, Y. Xiao, P. Chow, J. Zhao. Spin and valence states of iron in Al-bearing silicate glass at high pressures studied by synchrotron Mössbauer and X-ray emission spectroscopy. Am. Mineral., 99 (2–3) (2014), pp. 415-423

W.L. Mao, Y. Meng, G. Shen, V.B. Prakapenka, A.J. Campbell, D.L. Heinz, J. Shu, R. Caracas, R.E. Cohen, Y. Fei. Iron-rich silicates in the Earth's D ″layer. Proceedings of the National Academy of Sciences of the United States of America, 102 (28) (2005), pp. 9751-9753

W.L. Mao, H.-K. Mao, W. Sturhahn, J. Zhao, V.B. Prakapenka, Y. Meng, J. Shu, Y. Fei, R.J. Hemley. Iron-rich post-perovskite and the origin of ultralow-velocity zones. Science, 312 (5773) (2006), pp. 564-565

C. McCammon, R. Caracas, K. Glazyrin, V. Potapkin, A. Kantor, R. Sinmyo, C. Prescher, I. Kupenko, A. Chumakov, L. Dubrovinsky. Sound velocities of bridgmanite from density of states determined by nuclear inelastic scattering and first-principles calculations. Progress in Earth and Planetary Science, 3 (1) (2016), p. 10

M. Murakami, K. Hirose, K. Kawamura, N. Sata, Y. Ohishi. Post-perovskite phase transition in MgSiO3. Science, 304 (5672) (2004), pp. 855-858

M. Murakami, S.V. Sinogeikin, J.D. Bass, N. Sata, Y. Ohishi, K. Hirose. Sound velocity of MgSiO3 post-perovskite phase: A constraint on the D ″discontinuity. Earth Planet. Sci. Lett., 259 (1–2) (2007), pp. 18-23

M. Murakami, S.V. Sinogeikin, J.D. Bass, N. Sata, Y. Ohishi, K. Hirose. Sound velocity of MgSiO 3 post-perovskite phase: A constraint on the D ″discontinuity. Earth Planet. Sci. Lett., 259 (1) (2007), pp. 18-23

A.R. Oganov, S. Ono. Theoretical and experimental evidence for a post-perovskite phase of MgSiO3 in Earth's D ″layer. Nature, 430 (6998) (2004), pp. 445-448

K. Otsuka, S.-I. Karato. Deep penetration of molten iron into the mantle caused by a morphological instability. Nature, 492 (7428) (2012), pp. 243-246

C. Reasoner, J. Revenaugh. Short-period P wave constraints on D ″reflectivity. J. Geophy. Res. Solid Earth, 104 (B1) (1999), pp. 955-961

S.A. Russell, C. Reasoner, T. Lay, J. Revenaugh. Coexisting shear-and compressional-wave seismic velocity discontinuities beneath the central Pacific. Geophy. Res. Lett., 28 (11) (2001), pp. 2281-2284

R.L. Saltzer, E. Stutzmann, R.D. van der Hilst. Poisson's ratio in the lower mantle beneath Alaska: Evidence for compositional heterogeneity. J. Geophy. Res. Solid Earth, 109 (2004), p. B06301

D. Schlaphorst, C. Thomas, R. Holme, R. Abreu. Investigation of core–mantle boundary topography and lowermost mantle with P4KP waves. Geophysical Journal International, 204 (2) (2016), pp. 1060-1071

S.R. Shieh, T.S. Duffy, A. Kubo, G. Shen, V.B. Prakapenka, N. Sata, K. Hirose, Y. Ohishi. Equation of state of the postperovskite phase synthesized from a natural (Mg, Fe) SiO3 orthopyroxene. Proceedings of the National Academy of Sciences of the United States of America, 103 (9) (2006), pp. 3039-3043

C. Thomas, E.J. Garnero, T. Lay. High-resolution imaging of lowermost mantle structure under the Cocos plate. J. Geophy. Res. Solid Earth, 109 (2004), p. B08307

T. Tsuchiya, J. Tsuchiya. Effect of impurity on the elasticity of perovskite and postperovskite: Velocity contrast across the postperovskite transition in (Mg, Fe, Al)(Si, Al)O3. Geophy. Res. Lett., 33 (12) (2006), p. L12S04

T. Tsuchiya, J. Tsuchiya, K. Umemoto, R.M. Wentzcovitch. Phase transition in MgSiO3 perovskite in the earth's lower mantle. Earth Planet. Sci. Lett., 224 (3–4) (2004), pp. 241-248

M. Weber. P-and S-wave reflections from anomalies in the lowermost mantle. Geophy. J. Int., 115 (1) (1993), pp. 183-210

R.M. Wentzcovitch, T. Tsuchiya, J. Tsuchiya. MgSiO3 postperovskite at D ″conditions.“. Proceedings of the National Academy of Sciences of the United States of America, 103 (3) (2006), pp. 543-546

R.M. Wentzcovitch, J.J. Valencia-Cardona, J. Zhuang, G. Shukla, K. Sarkar. The Post-Perovskite Transition in Fe-and Al-Bearing Bridgmanite: Effects on Seismic Observables. J. Geophy. Res. Solid Earth, 128 (3) (2023), Article e2022JB025475

J.K. Wicks, J.M. Jackson, W. Sturhahn. Very low sound velocities in iron-rich (Mg, Fe) O: Implications for the core-mantle boundary region. Geophy. Res, Lett (2010), p. 37

J. Wookey, S. Stackhouse, J.-M. Kendall, J. Brodholt, G.D. Price. Efficacy of the post-perovskite phase as an explanation for lowermost-mantle seismic properties. Nature, 438 (7070) (2005), pp. 1004-1007

X. Wu, J.-F. Lin, P. Kaercher, Z. Mao, J. Liu, H.-R. Wenk, V.B. Prakapenka. Seismic anisotropy of the D″ layer induced by (001) deformation of post-perovskite. Nat. Commun., 8 (2017), p. 14669,

J. Zhang, T. Lay. Investigation of a lower mantle shear wave triplication using a broadband array. Geophy. Res. Lett., 11 (6) (1984), pp. 620-623