Characteristics of the upper mantle are typically deduced from mid-ocean and ocean island volcanics that sample the convecting mantle. However, a substantial fraction of the upper mantle is isolated from this convecting reservoir as part of the subcontinental lithosphere. This is a potentially significant reservoir; not only might there be substantial abundances of noble gases and other trace element constituents, but also re-entrainment of this material into the deeper mantle may ultimately impart unique isotopic signatures to mantle domains sampled at ocean islands (McKenzie and O’Nions 1983). The characteristics of the lithosphere can be deduced from magmas derived...

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