Post-Laramide, Eocene epeirogeny in central Colorado—The result of a mantle drip?

Abstract The Southern Rocky Mountains first rose during the Laramide Orogeny (ca. 75–45 Ma), but today's mountains and adjacent Great Plains owe their current height to later epeirogenic surface uplift. When why epeirogeny affected region are controversial. Sedimentation histories in two central Colorado basins, South Park–High Park Denver shifted at 56–54 Ma from an orogenic pattern, suggesting experienced that time. To interrogate hypothesis, we analyzed thermal for seven samples Colorado's Arkansas Hills High using thermochronometers with closure temperatures below ~180 °C, enabling us track sample exhumation ~5–7 km depth. Three Cretaceous Whitehorn pluton, four Precambrian granitoids. All zircon titanite (U-Th)/He dates (ZHe THe) one apatite fission-track (AFT) date similar 67 pluton emplacement age. lower-temperature (AHe) thermochronometer 55–41 Ma. These data require episodes, ca. 67–60 Ma, second beginning 54–46 reached by 37 based on age of volcanic tuff filling a pluton-cutting paleovalley. do not further refine this history owing comparatively higher He temperature more radiation-damaged apatite. crustal shortening caused exhumation. ended before so could have event began Ma; thermochronology supports Eocene hypothesis. Epeirogeny >2.0 × 104 km2, Sawatch Range Basin. We attribute mantle drip likely triggered subsequent drips, causing younger events areas.