Mio-Pliocene erosional exhumation of the central Colorado Plateau, eastern Utah: New insights from apatite (U-Th)/He thermochronometry

Abstract

The landscape evolution of the Colorado Plateau has been studied by scientists for over a century, yet its late Cenozoic erosional and geomorphic history remains poorly understood. This study investigates the temporal and spatial distribution, magnitude, and rate of erosional exhumation that has carved the spectacular modern landscape of the central Colorado Plateau. New thermochronometric data are presented from a swath of four regions in eastern Utah, namely the Monument Uplift, Canyonlands, Book Cliffs, and Uinta Basin, to establish the thermal and erosional history and reconstruct the long-term landscape evolution of the central Colorado Plateau. This thermochronometric study utilizes an integrated sampling approach which combines surface samples and cores in order to increase the vertical sampling window to more comprehensively quantify erosional exhumation. All apatite (U-Th)/He (AHe) ages from surface and core samples are younger than stratigraphic ages, suggesting complete or partial thermal resetting after deposition and burial. Core samples (depths 1 km) have proven critical to this study and indicate significant Mio-Pliocene cooling and exhumation at 6 Ma. Shallower cores and surface samples have a broad spread of Eocene to late Miocene ages (5-55 Ma), and indicate residence in the helium partial retention zone (HePRZ). Furthermore, AHe ages suggest a south to north progression in erosion on the Colorado Plateau. In Monument Uplift, 1.5-2 km of erosion is calculated, 2-3 km in Canyonlands, 0.9-2.2 km in the Book Cliffs, and 0.2-1.2 km in Uinta Basin. Accelerated erosional exhumation of the central Colorado Plateau in the late Miocene to early Pliocene is attributed to a combination of geologic events, including drainage integration of the Colorado River off the southwest Colorado Plateau, the opening of the Gulf of California, and the intensification of a southwest monsoon climate.