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Seismic velocities of CaSiO3 perovskite can explain LLSVPs in Earth’s lower mantle

Thomson, A; Crichton, W; Brodholt, J; Wood, I; Siersch, N; Muir, J; Dobson, D; (2019) Seismic velocities of CaSiO3 perovskite can explain LLSVPs in Earth’s lower mantle. [Letter]. Nature , 572 pp. 643-647. 10.1038/s41586-019-1483-x. Green open access

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Abstract

Seismology records the presence of various heterogeneities throughout the lower mantle1,2, but the origins of these signals—whether thermal or chemical—remain uncertain, and therefore much of the information that they hold about the nature of the deep Earth is obscured. Accurate interpretation of observed seismic velocities requires knowledge of the seismic properties of all of Earth’s possible mineral components. Calcium silicate (CaSiO3) perovskite is believed to be the third most abundant mineral throughout the lower mantle. Here we simultaneously measure the crystal structure and the shear-wave and compressional-wave velocities of samples of CaSiO3 perovskite, and provide direct constraints on the adiabatic bulk and shear moduli of this material. We observe that incorporation of titanium into CaSiO3 perovskite stabilizes the tetragonal structure at higher temperatures, and that the material’s shear modulus is substantially lower than is predicted by computations3,4,5 or thermodynamic datasets6. When combined with literature data and extrapolated, our results suggest that subducted oceanic crust will be visible as low-seismic-velocity anomalies throughout the lower mantle. In particular, we show that large low-shear-velocity provinces (LLSVPs) are consistent with moderate enrichment of recycled oceanic crust, and mid-mantle discontinuities can be explained by a tetragonal–cubic phase transition in Ti-bearing CaSiO3 perovskite.

Type: Article
Title: Seismic velocities of CaSiO3 perovskite can explain LLSVPs in Earth’s lower mantle
Open access status: An open access version is available from UCL Discovery
DOI: 10.1038/s41586-019-1483-x
Publisher version: https://doi.org/10.1038/s41586-019-1483-x
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10075628
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