Melting in the deep upper mantle oceanward of the Honshu slab

Brian Bagley, Anna M. Courtier, Justin Revenaugh

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33 Scopus citations


We examine the upper mantle and transition zone beneath the western Pacific using multiple ScS reverberations. A low-velocity zone (LVZ) is found above the 410-km discontinuity oceanward of the subducting Honshu slab at an average depth of 356 km, with a thickness that ranges from 50 to 75 km assuming the LVZ continues to the 410-km discontinuity, which is locally elevated. The low-velocity region is evident in previous tomographic studies, and our results suggest that the anomaly is best explained by a layer of partial melt. The layer may be entrained from above by subduction or produced in situ by the combined effects of water and temperature. A self-consistent model that explains local P-wave velocities (Obayashi, M., Sugioka, H., Yoshimitsu, J., Fukao, Y., 2006. High temperature anomalies oceanward of subducting slabs at the 410-km discontinuity. Earth and Planetary Science Letters 243, 149-158) and our observations calls for a maximum temperature anomaly of ∼150 °C and a resulting maximum olivine water content after melting of 0.100 wt. %.

Original languageEnglish (US)
Pages (from-to)137-144
Number of pages8
JournalPhysics of the Earth and Planetary Interiors
Issue number3-4
StatePublished - Jul 2009


  • Discontinuities
  • Low-velocity zone
  • Mantle
  • Partial melting
  • Transition zone
  • Water


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