New Mexico Geological Society Annual Spring Meeting — Abstracts

A regional compilation of apatite fission-track (AFT) and (U-Th)/He (AHe) data from surface and subsurface samples from the Colorado Plateau/ Rocky Mountain/ Rio Grande rift region reveals a multi-stage, episodic, exhumational history with Laramide (80-40 Ma), middle Cenozoic (35-25 Ma), middle to late Cenozoic (25-10 Ma), and late Cenozoic (110°C during subsequent tectonic events. Waning of extensive volcanism, elevated heat flow, and modification of crustal density structure following the ignimbrite flare-up (35-25 Ma) is recorded in cooling ages from S Colorado and New Mexico. Buoyancy caused by crustal modification lingered into the 25-10 Ma time frame, enhancing exhumation on the Colorado Plateau and High Plains. Extensional ranges along the margins of the Plateau also exhumed during this time interval. The 5- 10 Ma cooling ages in SW Colorado lie above profound low wave-speed anomalies in the uppermost mantle and are interpreted to place an upper bound on the timing of formation of these anomalies.