A Comparative Study of the Colorado Plateau, Tanzania Craton, and Ordos Basin

The Rigid Uplifted Block In eXtension (RUBIX) phenomenon is found in varying styles of extensional settings. The Colorado Plateau, Tanzania craton, and Ordos block/basin are tectonic blocks that have remained rigid relative to the expansion of the Basin and Range/Rio Grande rift, the rifting in east Africa, and the escape tectonics of East Asia, respectively. Although their geologic historic and modern tectonics vary, the blocks are of comparable geographic extents and are largely bounded by zones of extension. We have compared geologic, seismic, gravity, and geochemical data from the Colorado Plateau, Tanzania craton, and Ordos block/basin to see whether linear relations can be drawn between the three blocks to account for what cause(s) the RUBIX phenomenon. Ages for the Precambrian basement range from Paleo-proterozoic for the Colorado Plateau (1.6 to 2.0 Ga), to Neoarchean for the Tanzania craton (2.2 to 2.7 Ga), to Paleoarchean for the Ordos basin/block (>3.6 Ga). The amount of uplift varies with each feature, but all have uplifted rims that help define them as physiographic and tectonic entities. They all have played a role in the evolution of major rivers (the Colorado, Nile, and Yellow Rivers, respectively). Seismic and gravity data suggest that they each have a lithospheric root that is thick relative to adjacent areas. Also, geochemical data from xenoliths suggest that the mantle beneath the rigid blocks is more depleted than their adjacent areas. Our understanding of such phenomena is far from complete, but increased data availability has made it possible to make comparisons and better understand how structural blocks can maintain their integrity when surrounded by tectonic activity.