The active southwest margin of the Colorado Plateau: Uplift of mantle origin

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Abstract
During Cenozoic time, the Colorado Pla- teau was raised about 2 km above sea level. The most-recent and best-documented up- lift of the plateau (;1 km) has been con- centratedatitssouthwestmarginbetween6 and 1 Ma, whereas the eastern Colorado Plateau may,have been at high elevations sinceEocenetime.Tobetterunderstandthe recent tectonic activity at the southwest marginoftheColoradoPlateau,wecompile detailed crustal thickness and density in- formationfromseismicandgravitydatafor a region that includes northwest Arizona and the southern tip of Nevada. This infor- mation is used to isolate the mantle contri- bution to uplift. Wefind that there is rela- tively low density mantle underlying the southernmarginoftheplateauinnorthwest Arizona, which could result from about 60‐80 km,of thinning of the dense mantle lithosphere combined with about 100 &Cof heating through a 100-km-thick mantle layer. The available estimates from earth- quake-source seismology in or near the studyareaarecompatiblewiththisestimate of lithospheric thinning. We speculate that uplift may,result from subduction-related thinning of the continental lithosphere.

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