Small-scale convection at the edge of the Colorado Plateau: Implications for topography, magmatism, and evolution of Proterozoic lithosphere

Abstract

The Colorado Plateau of the southwestern United States is characterized by a bowl-shaped high elevation, late Neogene-Quaternary magmatism at its edge, large gradients in seismic wave velocity across its margins, and relatively low lithospheric seismic wave velocities. We explain these observations by edge-driven convection following rehydration of Colorado Plateau lithosphere. A rapidly emplaced Cenozoic step in lithosphere thickness between the Colorado Plateau and adjacent extended Rio Grande rift and Basin and Range province causes small-scale convection in the asthenosphere. A lithospheric drip below the plateau is removing lithosphere material from the edge that is heated and metasomatized, resulting in magmatism. Edgedriven convection also drives margin uplift, giving the plateau its characteristic bowl shape. The edge-driven convection model shows good consistency with features resolved by seismic tomography. province of the southwestern United States (Fig. 1A), consisting of largely extant Proterozoic lithosphere (ca. 1.7 Ga; Wendlandt et al., 1996;Gilbert et al., 2007) that was uplifted to its current elevation (~1.8 km) during the Cenozoic. Dynamic topography (Moucha et al.

Are ‘hot spots’ hot spots?

“…Warming of the thick Colorado Plateau lithosphere over 35-40 Ma following the removal of the Farallon slab can explain the time-scale of migration of Cenozoic magmatism from the margins towards the plateau interior, the lower seismic velocities, and the gravity field [Roy et al, 2009]. Edge-driven, small-scale mantle convection can explain the large gradients in seismic velocity across the margins of the plateau, the low lithospheric seismic velocities, continued, low-level volcanism, and the uplift [Van Wijk et al, 2010]. These proposed explanations do not invoke extremely high temperatures in the mantle, but only involve shallow convection.…”

A rootless rockies—Support and lithospheric structure of the Colorado Rocky Mountains inferred from CREST and TA seismic data

“…Additionally, some tomographybased mantle convection models for the western United States predict $1 km of present-day dynamic topography for the Colorado Plateau, declining eastward to 100-500 m of uplift across the CRM [Forte et al, 2010;Liu and Gurnis, 2010;Moucha et al, 2008]. Small-scale convection has also been proposed in this region [van Wijk et al, 2010] and may be affecting the current CRM topography [Coblentz et al, 2011].…”

“…Flexure modeling demonstrates that buoyancy resulting from a combination of low-density crust and elevated mantle temperature is sufficient to explain the excess topography of the CRM relative to the Colorado Plateau and High Plains (Figure 8). Therefore, no local mantle flow pressures associated with smallscale convection [Coblentz et al, 2011;van Wijk et al, 2010] are required to support the topography of the CRM. However, some form of advective heat/mass transfer is almost certainly required by the inferred mantle temperature variations which reach 600 C. It is important to note that our analysis is insensitive to topographic mean and any absolute elevation changes [e.g., Karlstrom et al, 2012] as only the relative density differences are utilized for flexure modeling (Appendix A).…”

Plateau uplift in western Canada caused by lithospheric delamination along a craton edge

“…Small-scale thermal-chemical convection associated with this proto-step may have played a pivotal role in the initiation of delamination. Previous studies 9,21,22,26 show that upwelling asthenospheric flow due to edge-driven convection can destabilize previously hydrated lithosphere by refertilization and shearing, causing a significant density increase and viscosity decrease. Basal shearing may have resulted in stress and strain concentration along the RMT, a deep rheological boundary, leading to peeling off of a segment of lithospheric mantle.…”