LATE CENOZOIC EVOLUTION OF THE SOUTHERN ROCKY MOUNTAINS

New constraint regarding the tectonic origin and significance of the southern Rocky Mountains and Colorado Plateau is provided by results from the Continental Dynamics Rocky Mountain Project (CDROM), Deep Probe, the Rio-Grande Rift Seismic Transect (RISTRA) and new surface wave mantle velocity images. From this, we propose a simple model to explain the origin of the late Cenozoic uplift, volcanism, Xenolith P-T-t curves, heat flow, and late Cenozoic rifting of the southern Rocky Mountains. Simply put, a variably hydrated and chemically heterogeneous lithosphere is being reheated from below by emplacement of warmer than normal mantle at the base of the lithosphere. This reheating from below is consistent with multiple seismic studies that show a negative velocity gradient extending to about 150 km depth. The lithosphere’s ongoing volcano-tectonic response to this input of mantle heat is modulated by the pre-existing chemically “blocky” lithosphere (as suggested by new seismic tomography and mantle layering images). A primary consequence of this reheating is that the late-Cenozoic isostatic uplift of this region whose net effect has enhanced the gravitational potential energy available to drive formation of the Rio Grande Rift. Comparison of this region mantle velocity structure, volcanic geochemistry, uplift history and deformation show a striking similarity with two other late-Cenozoic regions of uplift, volcanism and rifting: the East African Rift and the Mongolian Dome/Baikal Rift, suggesting a common origin (i.e., reheating from below) for all three regions.