IMPACT OF BUOYANT MANTLE UPWELLINGS ON THE SURFACE EVOLUTION OF NORTH AMERICA: IMPLICATIONS FOR TOPOGRAPHY CHANGES IN THE SOUTHWESTERN AND EASTERN U.S

Seismic tomography is now widely regarded as the essential starting ingredient in any attempt to construct realistic models of the mantle convective flow and predicting a wide range of convection-related surface observables. This recognition has been the central motivation for the development of a new series of global tomography models that are derived from the simultaneous inversion of seismic and convection-related data sets that provide a highly successful reconciliation of 3-D mantle structure with the associated mantle-wide convective circulation (Simmons et al., GRL 2007, GJI 2009, JGR2010).

These joint seismic-geodynamic tomography models are used in mantle convection simulations that provide detailed insights on how mass and heat transport across the mantle affect the surface dynamics of our planet, on both global and regional scales (e.g. Moucha et al., EPSL 2008; Moucha & Forte, Nat. Geosci. 2011; Glisovic et al., GJI 2012). These dynamic models reveal, in particular, the major impact of hot upwellings on the topographic evolution of our planet. We review findings for a large-scale plume upwelling under the Southwestern U.S. over the past 30 Ma that generated a topographic swell that correlates with geologic evidence for a wave of uplift that began in the central Basin and Range province and progressed under the Colorado Plateau (Moucha et al., GRL 2009). We also review recent work that shows a more geologically recent, but equally profound impact of hot upwelling mantle under the Atlantic Coast of the U.S., generating a wave of variable uplift along the Eastern seaboard since Pliocene times (Rowley et al., Sci. 2013).

We finally discuss the relevance of these findings for new high-resolution images of 3-D mantle structure under the U.S. obtained from inversions of seismic data collected by the Earthscope Transportable Array. A complete dynamical interpretation of these detailed images of heterogeneity in the upper mantle under the U.S. must include the impact of the 'mantle wind': the strong large-scale flow that is generated by deep-seated buoyancy located in the lower mantle (Forte, Treatise of Geophysics 2nd Ed. 2013). The successful integration of the dynamical connections between lower-mantle structure with the new high-resolution models of upper-mantle heterogeneity is an outstanding challenge.