Seismic anisotropy, dominant slip systems and phase transitions in the lowermost mantle

Brian Chase Chandler, Li Wei Chen, Mingming Li, Barbara Romanowicz, Hans Rudolf Wenk

Research output: Contribution to journalArticlepeer-review

Abstract

The presence of seismic anisotropy at the base of the Earth's mantle is well established, but there is no consensus on the deformation mechanisms in lower mantle minerals that could explain it. Strong anisotropy in magnesium post-perovskite (pPv) has been invoked, but different studies disagree on the dominant slip systems at play. Here, we aim to further constrain this by implementing the most recent results from atomistic models and high-pressure deformation experiments, coupled with a realistic composition and a 3-D geodynamic model, to compare the resulting deformation-induced anisotropy with seismic observations of the lowermost mantle. We account for forward and reverse phase transitions from bridgmanite (Pv) to pPv. We find that pPv with either dominant (001) or (010) slip can both explain the seismically observed anisotropy in colder regions where downwellings turn to horizontal flow, but only a model with dominant (001) slip matches seismic observations at the root of hotter large-scale upwellings. Allowing for partial melt does not change these conclusions, while it significantly increases the strength of anisotropy and reduces shear and compressional velocities at the base of upwellings.

Original languageEnglish (US)
Pages (from-to)1665-1681
Number of pages17
JournalGeophysical Journal International
Volume227
Issue number3
DOIs
StatePublished - Nov 1 2021

Keywords

  • Mantle processes
  • Phase transitions
  • Plasticity, diffusion, and creep
  • Rheology: mantle
  • Seismic anisotropy

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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