CONVECTIVE REMOVAL OF COLORADO PLATEAU LITHOSPHERE FROM THE OUTSIDE-IN AND RESULTING MAGMATISM AND SURFACE UPLIFT

A number of different lines of evidence suggest that the Paleoproterozoic mantle lithosphere and possibly the lower crust under the Colorado Plateau are being convectively removed from the outside-in. Rayleigh wave tomography and Ps and Sp receiver function (RF) images show that the lithosphere thins from ~130 km in the plateau center to 55-75 km within 50-100 km of its boundaries with the Basin and Range province and the Rio Grande rift (Liu et al., 2011; Levander and Miller, 2012, Bailey et al, 2012). Teleseismic body wave tomography shows at least two compact high velocity anomalies, nearly circular in map view, extending from the base of the CP lithosphere to depths of 200+ km in the west central and southern parts of the plateau (Schmandt and Humphreys, 2010; Obrebski et al., 2011). Ps and Sp RF imaging also suggests that the lower crust is involved in a delamination-like downwelling under the west central plateau (Levander et al., 2011), with other RF studies showing crustal involvement in the northwestern plateau in the form of thicker than normal crust and weak Moho signatures (Wilson et al., 2010). Mid-Tertiary to recent magmatism has invaded the plateau from the outside-in at different rates around the boundary (Wenrich et al., 1995; Roy et al., 2009; Crow et al., 2011), and is confined to areas where the lithosphere is seismically determined to be thin. A variety of geochemical signatures imply a peridotite source for much of the volcanism, likely melting of a reactivated chemical boundary layer and fertile asthenosphere (Crow et al., 2011; Reid et al., 2012), rather than in situ lithospheric melting or melting of descending mantle drips. Recent magmatism is spatially correlated with the downwellings. Large wavelength surface uplift also appears well correlated with the location of the downwelling beneath the western plateau (Pederson et al., 2013), implying deep control on surface processes. The combined data suggest that the CP lithosphere is being removed progressively from the outside-in, driving recent uplift. We envision a cascading downwelling-delamination process caused by 3D thermo-chemical edge convection, showing many aspects of the geodynamic modeling of Van Wijk et al, (2010, 2012, 2013).