Development of finite strain in the convecting lower mantle and its implications for seismic anisotropy

Allen K. McNamara, Peter E. van Keken, Shun Ichiro Karato

Research output: Contribution to journalArticle

47 Citations (Scopus)

Abstract

Seismological observations have revealed patches of seismic anisotropy in regions related to mantle upwelling and paleosubduction within an otherwise isotropic lower mantle. A combination of numerical modeling and mineral physics is used to constrain the source of anisotropy in these regions in an effort to better understand lower mantle dynamics and mineral physics. Specifically, it is investigated whether lattice-preferred orientation (LPO) can explain the anisotropy observed in regions of paleosubduction. Since LPO is caused by dislocation creep and is destroyed by diffusion creep, we can develop deformation mechanism maps to determine which regions allow for the development of a mineral fabric. Strain is then calculated in these regions and is related to mineral physics experiments combined with high-pressure elastic constants of lower mantle minerals in order to assess the predicted seismic anisotropy. Uncertainties in rheological parameters such as the transition stress between dislocation creep and diffusion creep necessitate a full evaluation of the parameter range. The effect of variations in transition stress, activations parameters, and strength of slabs on fabric development is investigated. It is shown that LPO is a likely candidate for the cause of lowermost mantle anisotropy in regions of paleosubduction.

Original languageEnglish (US)
JournalJournal of Geophysical Research B: Solid Earth
Volume108
Issue number5
StatePublished - May 10 2003
Externally publishedYes

Fingerprint

seismic anisotropy
lower mantle
Minerals
Earth mantle
Anisotropy
minerals
Creep
anisotropy
preferred orientation
Physics
mineral
dislocation creep
physics
creep
upwelling water
Elastic constants
deformation mechanism
slabs
elastic properties
Chemical activation

Keywords

  • Anisotropy
  • Dislocation
  • Mantle convection
  • Seismic
  • Strain

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)
  • Atmospheric Science
  • Geochemistry and Petrology
  • Geophysics
  • Oceanography
  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Development of finite strain in the convecting lower mantle and its implications for seismic anisotropy. / McNamara, Allen K.; van Keken, Peter E.; Karato, Shun Ichiro.

In: Journal of Geophysical Research B: Solid Earth, Vol. 108, No. 5, 10.05.2003.

Research output: Contribution to journalArticle

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