EXHUMATION IN THE ROCKY MOUNTAINS: EXPLORING TIMING, RATES, MECHANISMS, AND UPLIFT MODELS USING COMPILED THERMOCHRONOLOGY DATA

A regional compilation of published apatite fission-track (AFT) and (U-Th)/He (AHe) data through the Rocky Mountains from New Mexico to Wyoming reveals spatial and temporal patterns in the timing of cooling that may be associated with different uplift episodes, exhumation rates, and mechanisms. A database of 1200 AFT (~110°C closure) and 100 AHe (~ 60°C closure) dates from across the region suggests three exhumation events and three different uplift mechanisms: 1) 70-45 Ma cooling ages are located in Laramide uplifts in the Wyoming Wind River, Medicine Bow and Park Ranges, Colorado Front and Park, and some Colorado Plateau monoclines, with typical cooling rates of 60m/Ma from 70-45 Ma; 2) There was relative tectonic quiescence from 45-35 Ma; 3) Oligocene 35-25 Ma cooling ages reflect uplift and denudation (and some reheating) associated with the ignimbrite flare-up beneath the San Juan and Mogollon Datil volcanic fields and creating the Great Plains topographic ramp, with exhumation rates of 100 m/Ma from 35-25Ma and long wavelength uplift and erosion reflecting epeirogenic mantle upwelling; 4) continued regional exhumation 25-10 Ma in the Elk Range, the Sawatch, and San Juans, and short wavelength rift-flank uplifts like Blanca Peak, the Sandias, the Ladrons in New Mexico; and 5) Neogene cooling ages reflect acceleration of cooling and exhumation to rates >120m/Ma with shorter wavelength uplift reflecting small scale upper mantle convection that reactivates a heterogeneous crustal fault-block structure. Estimation of cooling rates is derived from the best behaved (linear) age- elevation data arrays that suggest cooling due to exhumation with minimal complexity due to reheating and advection of isotherms. The power of applying both AFT and AHe to the same suite of rocks is that it allows a cross check of both systems and, in ideal cases, offers a way to track rocks through 110-60°C, with the potential that thermochronology data can be linked to long term incision rate data from dated river terraces to give a more complete history of exhumation from ~ 3 km to the surface to investigate differential exhumation across the Colorado Plateau-Rocky Mountain region.