Late Cenozoic volcanism, uplift and erosion, southern Sangre de Cristo Mountains, New Mexico
J. Michael O'Neill and Harold H. Mehnert
The Ocate volcanic field in northeastern New Mexico lies abreast the structural transition zone between the Southern Rocky Mountains and the Great Plains physiographic provinces. The field consists of numerous basaltic flows and minor andesitic to dacitic differentiates. The flows are of limited extent and range in age from Miocene to Pleistocene. The physiographic expression of these flows reflects their ages. The oldest flows, between 8.1 and 5.6 Ma, cap the highest mesas. These flows are underlain by stream gravels and appear to rest on remnants of a single surface or a series of nearly equivalent surfaces cut into the mountain interior at elevations near 3000 m. Numerous accordant ridge tops, subsummits and parks in the adjacent Taos and Cimarron Ranges are also at elevations near 3000 m and suggest that this surface was widespread during late Miocene time. The surface cuts across major Laramide structures and the various lithologies of the mountain interior; it extends eastward onto the Great Plains. The early volcanism was followed by episodic uplift and erosion now marked by three lower erosion surfaces. These surfaces are also preserved beneath volcanic rocks that are 5 to 4 Ma, 3.3 to 3 Ma and 2.2 Ma. Of the four erosion surfaces, the two oldest are now warped and locally displaced where they cross the older Laramide fault zones, indicating that late Cenozoic uplift of the region involved differential movement between the Rocky Mountains and the Great Plains. Young basalts, having an age of 1.4 Ma, followed major stream valleys and are now perched nearly 125 m above present stream levels. Finally, basalts 0.8 Ma were erupted mainly onto older flows.
- O'Neill, J. Michael; Mehnert, Harold H., 1990, Late Cenozoic volcanism, uplift and erosion, southern Sangre de Cristo Mountains, New Mexico, in: Tectonic development of the southern Sangre de Cristo Mountains, New Mexico, Bauer, Paul W.; Lucas, Spencer G.; Mawer, Christopher K.; McIntosh, William C., New Mexico Geological Society, Guidebook, 41st Field Conference, pp. 349-353.