REMNANTS OF PROTEROZOIC FLAT-SLAB SUBDUCTION BENEATH THE MID-CONTINENT, USA
This seismically slow region cannot be explained through elevated mantle temperatures, and while we cannot rule out a potential deep-mantle plume, we do not deem the scenario likely in the context of geological, geochemical, and other geophysical studies of the region. Currently we believe that the anomaly is most straightforwardly explained by an unusual crust-mantle mixture, where either 1.) oceanic crust became incorporated in the mantle of an over-riding plate during a Proterozoic episode of flat-slab subduction, or 2.) a relatively cool mantle wedge is preserved with hydrous minerals. In either case a flat dip-angle is necessary to avoid slab dehydration and associated partial melting of the mantle, which would deplete the mantle and eventually result in a seismically fast lithosphere. A receiver function analysis could further differentiate between the mantle plume and flat-slab hypotheses.