Western U.S. seismic anisotropy revealing complex mantle dynamics

Quan Zhou, Jiashun Hu, Lijun Liu, Thomas Chaparro, Dave R. Stegman, Manuele Faccenda

Research output: Contribution to journalArticle

Abstract

The origin of the complex pattern of SKS splitting over the western United States (U.S.) remains a long-lasting debate, where a model that simultaneously matches the various SKS features is still lacking. Here we present a series of quantitative geodynamic models with data assimilation that systematically evaluate the influence of different lithospheric and mantle structures on mantle flow and seismic anisotropy. These tests reveal a configuration of mantle deformation more complex than ever envisioned before. In particular, we find that both lithospheric thickness variations and toroidal flows around the Juan de Fuca slab modulate flow locally, but their co-existence enhances large-scale mantle deformation below the western U.S. The ancient Farallon slab below the east coast pulls the western U.S. upper mantle eastward, spanning the regionally extensive circular pattern of SKS splitting. The prominent E–W oriented anisotropy pattern within the Pacific Northwest reflects the existence of sustaining eastward intrusion of the hot Pacific oceanic mantle to beneath the continental interior, from within slab tears below Oregon to under the Snake River Plain and the Yellowstone caldera. This work provides an independent support to the formation of intra-plate volcanism due to intruding shallow hot mantle instead of a rising mantle plume.

Original languageEnglish (US)
Pages (from-to)156-167
Number of pages12
JournalEarth and Planetary Science Letters
Volume500
DOIs
StatePublished - Oct 15 2018

Keywords

  • Farallon slab
  • Juan de Fuca subduction
  • complex mantle dynamics
  • hot mantle intrusion
  • lithosphere thickness variation
  • western U.S. seismic anisotropy

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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