Formation of cratonic mantle keels by arc accretion: Evidence from S receiver functions

Delineating mantle interfaces can provide important clues for understanding the formation of continents. We use S-wave receiver functions to investigate lithospheric structure along a transect extending from Vancouver Island to Baffin Island. Observed Sp converted waves allow for interpretation of boundaries in the depth range expected for tectonic plates. Receiver functions show a distinct negative amplitude feature, interpreted as the lithosphere-asthenosphere boundary, at shallow depths beneath British Columbia (∼85km), deepening abruptly at the eastern edge of the Cordillera to ∼260km beneath the Canadian Shield. Dipping mid-lithospheric discontinuities extend beneath several giant ca. 1.8 Ga epicontinental magmatic arcs, consistent with formation of cratonic lithosphere by arc accretion. This model provides a plausible explanation for global mid-lithospheric discontinuities within cratons and aids in understanding their formation.