Lithospheric density models reveal evidence for Cenozoic uplift of the Colorado Plateau and Great Plains by lower-crustal hydration

Abstract

Subduction at plate boundaries can have thermal, chemical, and physical impacts on broad regions of the continental interior, but these interactions are not as readily obvious as deformation near the continental margin. Such cryptic alteration has produced surface uplift in the Colorado Plateau and western Great Plains of North America, which have risen-largely undeformed-1.6 and 1.3 km, respectively, relative to the eastern Great Plains during the Cenozoic. Accumulation of Cretaceous-Cenozoic sediments accounts for only 300 m of uplift of the Colorado Plateau and 400 m of the western Great Plains, leaving 1.3 km and 0.9 km, respectively, unexplained. To determine the physical causes of this enigmatic epeirogeny, we derived three-dimensional (3-D) lithospheric density models from seismic velocity, gravity, topography, and heatflow data. Lower-crustal density decreases systematically westward across the Great Plains, accounting nearly perfectly for the remaining 900 m of uplift of the western Great Plains and the modern east-west topographic gradient. Lower-crustal dedensification beneath the Colorado Plateau accounts for a similar 900 m of uplift. Lower-crustal xenoliths in both regions show progressive hydration-induced retrogression of garnet-bearing assemblages with increasing modern elevation, and Th-Pb dating of the Colorado Plateau retrogression gives end-Cretaceous dates (xenoliths from the Great Plains have not yet been dated). We hypothesize that lower-crustal density variations-and much of the surface relief-in North America's Proterozoic interior terranes reflect varying degrees of metasomatic retrogression, such as by fluids exsolved from the Farallon slab. The remaining 400 m of Colorado Plateau uplift is most plausibly due to elevated mantle temperature. We present thermal models that suggest that 25-70 km of Cenozoic lithospheric thinning can explain the modern elevation and density structure.

Quantitative Relationships Between Basalt Geochemistry, Shear Wave Velocity, and Asthenospheric Temperature Beneath Western North America

“…Large misfits occur at the transition between western and cratonic North America toward the eastern end of this transect, on the Colorado Plateau, and adjacent to the Great Plains volcanic province. Across western North America, the proportion of elevation that is generated and maintained by asthenospheric thermal anomalies appears to be <300 m, in agreement with previous isostatic studies (Levandowski et al, 2014(Levandowski et al, , 2018. Across western North America, the proportion of elevation that is generated and maintained by asthenospheric thermal anomalies appears to be <300 m, in agreement with previous isostatic studies (Levandowski et al, 2014(Levandowski et al, , 2018.…”

“…This substantial elevation difference can only be maintained by crustal isostasy if crust beneath the Great Plains is 0.15 Mg/m 3 denser than crust beneath the elevated plateaux. Thus, simple isostatic constraints indicate that the topographic elevation of western North America is supported by density variations within the lithospheric and/or the sublithospheric mantle (Levandowski et al, 2018). Thus, simple isostatic constraints indicate that the topographic elevation of western North America is supported by density variations within the lithospheric and/or the sublithospheric mantle (Levandowski et al, 2018).…”

Continental‐Scale Landscape Evolution: A History of North American Topography

“…The geomorphic modeling and stratigraphic observations presented here suggest that regional uplift of western North American topography has predominated. Isostatic considerations indicate that the present‐day surface elevation of this extensive region is supported by density variations within and beneath the lithospheric mantle rather than by crustal thickening (e.g., Levandowski et al., ). Rare earth element inverse modeling of <5 Ma basaltic melts with Ocean Island Basalt affinities combined with the presence of shear wave velocity anomalies constrained by earthquake tomographic models are consistent with moderately elevated mantle potential temperatures and thin (∼70 km) lithosphere beneath western North America (Klocking et al., ).…”

“…Colored circles = zircon ages (Blum et al, 2017). generating and maintaining the regional elevation of western North America since Late Cretaceous times (Spencer, 1996;Wilson et al, 2005). The observed velocity structure of the crust indicates that differences in crustal and sedimentary densities alone are insufficient to account for these dramatic changes in topographic relief (Klocking et al, 2018;Levandowski et al, 2018;.…”

Unravelling the lithospheric-scale thermal field of the North Patagonian Massif plateau (Argentina) and its relations to the topographic evolution of the area

“…In addition, the Colorado Plateau, again similar to the NPM, was affected by basaltic volcanism that erupted from the top of the plateau to the lower elevated areas in its surroundings after the uplift. Supported by a far larger amount of geophysical data, the Colorado Plateau is interpreted to have a thicker crust with respect to the surrounding B&R crust (43-49 km; Keller et al 1979;McQuarrie and Chase 2000;Sheehan et al 1997;Zandt et al 1995), a pronounced low velocity zone in mantle below the southern portion of the plateau (Levander et al 2011) and elevated temperatures (Hinojosa and Mickus 2002;Levandowski et al 2018;Reiter et al 1979;Roy et al 2009). These similarities with the NPM plateau point to a similar origin and similar mechanisms at work maintaining their respective elevations.…”