Spin Crossover in Ferropericlase at High Pressure: A Seismologically Transparent Transition?

• Published in: Science (American Association for the Advancement of Science) 2011-01, Vol.331 (6013), p.64-67
• Main Authors: Antonangeli, Daniele, Siebert, Julien, Aracne, Chantel M, Farber, Daniel L, Bosak, A, Hoesch, M, Krisch, M, Ryerson, Frederick J, Fiquet, Guillaume, Badro, James
• Format: Article
• Language: English
• Subjects: Anisotropy; Chemical properties; Congenital Impairments; Crossovers; Crystalline rocks; Deviation; Earth; Earth Sciences; Earth, ocean, space; Earthquakes, seismology; Elastic scattering; Exact sciences and technology; Experimental petrology; Geophysics; High pressure; Internal geophysics; Iron; Lower mantle; Mantle; Mineralogy; Minerals; Moduli of elasticity; Particle velocity; Perovskites; Pressure; Sciences of the Universe; Seismic engineering; Seismic phenomena; Seismic waves; Seismology; Shear; Shear modulus; Signatures; Solid-earth geophysics, tectonophysics, gravimetry; Sound waves; Ultrasonics; Wave velocity
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1198429

Seismic discontinuities in Earth typically arise from structural, chemical, or temperature variations with increasing depth. The pressure-induced iron spin state transition in the lower mantle may influence seismic wave velocities by changing the elasticity of iron-bearing minerals, but no seismological evidence of an anomaly exists. Inelastic x-ray scattering measurements on (Mg₀.₈₃Fe₀.₁₇)O-ferropericlase at pressures across the spin transition show effects limited to the only shear moduli of the elastic tensor. This explains the absence of deviation in the aggregate seismic velocities and, thus, the lack of a one-dimensional seismic signature of the spin crossover. The spin state transition does, however, influence shear anisotropy of ferropericlase and should contribute to the seismic shear wave anisotropy of the lower mantle.