Segmentation of the Farallon slab

Lijun Liu, Dave R. Stegman

Research output: Contribution to journalArticlepeer-review


Recent tomography images reveal a complex 3D mantle structure beneath western United States, with feature morphology varying rapidly with depth. By assimilating plate motion history, paleo-age of sea floor, and paleo-geography of plate boundaries in a 3-D numerical model, we simulate the Farallon-Juan de Fuca subduction during the past 40Ma. We find that the highly segmented upper mantle structure of western U.S. is a direct result of the Farallon subduction. We show that the tilted 'horseshoe'-shaped fast seismic anomaly beneath Nevada and Utah at 300-600km depth range is in fact a segment of curled slab subducted since 15Ma, and the shallower linear slab beneath the Cascades is younger than 5Ma. The distinct morphology between these two parts of the subduction system indicates the strong influence of the fast trench rollback since 20Ma, the northward migrating JF-PA-NA triple-junction, and the toroidal flow around slab edges. The observed mantle structures are used to constrain the rheology of the upper mantle through matching the shape, depth, and location of modeled subducted slab segments. The inferred viscosity for the asthenosphere is 5×1019Pas and those for the transition zone and lower mantle are 1.5×1021Pas and 2×1022Pas, respectively. The slab is found to be about 2 orders of magnitude stronger than the ambient mantle above 410km depth, but of similar order of magnitude viscosity in the transition zone.

Original languageEnglish (US)
Pages (from-to)1-10
Number of pages10
JournalEarth and Planetary Science Letters
Issue number1-2
StatePublished - Nov 1 2011
Externally publishedYes


  • B&R extension
  • Farallon subduction
  • Seismic tomography
  • Slab segmentation
  • Toroidal mantle flow
  • Viscosity

ASJC Scopus subject areas

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


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