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Radial thermo-chemical structure beneath Western and Northern Pacific from seismic waveform inversion

Abstract : The Earth's deep mantle seismic structure is dominated by two large low shear-wave velocity provinces (LLSVPs) located beneath Africa and the Pacific. While the existence of these structures has been attested by many studies and data sets, their detailed nature, purely thermal or thermo-chemical, is still a matter of debate. Discriminating between these hypotheses requires constraints independent from seismic velocity structure. Seismic shear-wave attenuation, measured by the quality factor QS, strongly depends on temperature but not (or weakly) on composition. It may bring key information on temperature, resolving in turn the trade-off between temperature and composition. Here, we invert seismic waveform data for radial models of shear-wave velocity anomalies (dlnVS), and QS at two different locations in the Pacific, and from a depth of 2000 km down to the core-mantle boundary (CMB). We show that Western Pacific (WP) models, sampling the western tip of the Pacific LLSVP and the Caroline plume, cannot be explained by thermal anomalies alone, but require excess in iron of ∼4.0% from the CMB up to 2600 km. By contrast, Northern Pacific models (NP), if unaffected by seismic anisotropy, may have a purely thermal origin. Based on these observations, we build radial thermo-chemical models at WP and NP.
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https://hal-insu.archives-ouvertes.fr/insu-03586635
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Submitted on : Thursday, February 24, 2022 - 8:33:45 AM
Last modification on : Tuesday, May 17, 2022 - 5:08:02 PM

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Frédéric Deschamps, Kensuke Konishi, Nobuaki Fuji, Laura Cobden. Radial thermo-chemical structure beneath Western and Northern Pacific from seismic waveform inversion. EARTH AND PLANETARY SCIENCE LETTERS, 2019, 520, pp.153-163. ⟨10.1016/j.epsl.2019.05.040⟩. ⟨insu-03586635⟩

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