The 'subduction initiation rule': A key for linking ophiolites, intra-oceanic forearcs, and subduction initiation

Scott A. Whattam, Robert J. Stern

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347 Citations (Scopus)


We establish the 'subduction initiation rule' (SIR) which predicts that most ophiolites form during subduction initiation (SI) and that the diagnostic magmatic chemostratigraphic progression for SIR ophiolites is from less to more HFSE-depleted and LILE-enriched compositions. This chemostratigraphic evolution reflects formation of what ultimately becomes forearc lithosphere as a result of mantle melting that is progressively influenced by subduction zone enrichment during SI. The magmatic chemostratigraphic progression for the Izu-Bonin-Mariana (IBM) forearc and most Tethyan ophiolites is specifically from MORB-like to arc-like (volcanic arc basalts or VAB ± boninites or BON) because SI progressed until establishment of a mature subduction zone. MORB-like lavas result from decompression melting of upwelling asthenosphere and are the first magmatic expression of SI. The contribution of fluids from dehydrating oceanic crust and sediments on the sinking slab is negligible in early SI, but continued melting results in a depleted, harzburgitic residue that is progressively metasomatized by fluids from the sinking slab; subsequent partial melting of this residue yields 'typical' SSZ-like lavas in the latter stages of SI. If SI is arrested early, e.g., as a result of collision, 'MORB-only' ophiolites might be expected. Consequently, MORB- and SSZ-only ophiolites may represent end-members of the SI ophiolite spectrum. The chemostratigraphic similarity of the Mariana forearc with that of ophiolites that follow the SIR intimates that a model linking such ophiolites, oceanic forearcs, and SI is globally applicable.

Original languageEnglish
Pages (from-to)1031-1045
Number of pages15
JournalContributions to Mineralogy and Petrology
Issue number5
Publication statusPublished - 2011 Nov

Bibliographical note

Funding Information:
Acknowledgments RJS thanks many of his colleagues who helped him over the years understand what happens during subduction initiation, including Sherm Bloomer, Yildirim Dilek, Mike Gurnis, Osamu Ishizuka, Yas Ohara, Hadi Shafaii Moghadem, Julian Pearce, Mark Reagan, and John Shervais. These insights would not have been possible without support from the National Science Foundation.


  • Forearcs
  • Intra-oceanic arcs
  • Izu-Bonin-Marianas arc
  • Ophiolites
  • Subduction initiation
  • Tethys

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology


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