THE COLORADO PLATEAU'S LITHOSPHERIC STRUCTURE AND ANALOGIES WITH SIMILAR TECTONIC FEATURES

The Colorado Plateau is a classic geologic wonder and high standing physiographic feature that has been traversed by the Colorado River. The plateau is bounded by zones of Cenozoic extension that have a relatively thin (30-35km) crust, and its interior is also generally in extension today. Young volcanic fields extend across the plateau’s margins in three localities. Recent petrologic and seismic tomographic studies (e.g. Mahan et al., 2017; Porter et al., 2017; Levandowski et al., 2018) indicate that hydration of the lower crust by subduction of the Farallon Plate is a major factor in producing the elevation of the plateau. In addition, young volcanic fields extend across the plateau’s margins in three localities. However, the effects of the Pacific slab subuction have made determining the thickness of the sub-crustal lithosphere with certainty very difficult, but the crustal thickness is generally viewed to be 40-45 km.

The Colorado Plateau is certainly a tectonic block, and we can learn by studying similar features. A particlarly interesting analogy can be drawn with the Tanzanian Craton that, like the Colorado Plateau, is bounded by two modern rifts (Kenyan and Western) with Lake Victoria in its center. The fact that the East African rift splits to produce two arms that bound the Tanzanian Craton attests to the existence of a deep lithospheric keel beneath it. Another well-studied feature that is very similar in many regards is the Ordos Plateau in southeast China. An interesting difference is that the Colorado River managed to cut right through the Colorado Plateau and produce the Grand Canyon while the mighty Yangtze River winds around the northern margin of the Ordos Plateau. These analogies remind us that our continents consist of many tectonic blocks and many may be buried and unrecognized. An example is the proposed subsurface Sabine Terrane that extends completely across Louisiana from the Ouachita Orogen to the Gulf of Mexico.