PRESENT-DAY CRUSTAL DEFORMATION ACROSS THE COLORADO PLATEAU AND RIO GRANDE RIFT MEASURED BY GPS

The Colorado Plateau and Rio Grande Rift are two key tectonic features within the Pacific-North America plate boundary zone. Past studies have suggested that the Colorado Plateau has been a rigid entity for much of its history and that its Neogene clockwise rotation has resulted in the opening of the Rio Grande Rift. We present velocities from many (mostly new) continuous GPS stations and discuss the implied present-day deformation rates and patterns. Within measurement uncertainty, only sites along the Plateau’s central longitudes move as a coherent block around a pole of rotation in the northern Rockies and with a maximum rate along the Plateau’s southern margin of 1.4 mm/yr relative to stable North America. Stations in the southwestern Plateau, east of the Hurricane and Toroweap normal faults, move westward at ~0.5 mm/yr relative to the Plateau’s rigid core. Westward motion reaches 1.6 mm/yr near the longitude of Las Vegas. Relative to the Plateau’s rigid core, sites in northwestern and southwestern New Mexico move ~0.2 mm/yr and ~0.5 mm/yr eastward, respectively. There is no clear extensional across the Rio Grande Rift proper, but E-W extension of ~1 mm/yr between the Great Plains and the Colorado Plateau can be detected. The Jemez Lineament may be more important than the Rio Grande Rift in accommodating (some of) the extension. Regionally, areas of extension seem to be correlated with areas of thin lithosphere and extension appears to be encroaching into the Colorado Plateau from both the east and west. The relationship between active extension, recent magmatism, and crustal/mantle structure suggests an active mantle control on present-day surface deformation.