Bridging classical low-temperature thermochronology and geomorphology: ESR thermochronology constraints on Plio-Quaternary exhumation and canyon incision across the Colorado Plateau

The timing and drivers of canyon incision across the Colorado Plateau are strongly debated, particularly the roles of deep-seated processes, tectonics, geological inheritance, and climate. A major limitation in resolving canyon incision histories and their controlling processes is that the amount of exhumation associated with incision is often too small to be robustly recorded by classical low-temperature thermochronometers such as apatite fission track and (U–Th)/He. Resolving the timing of exhumation acceleration and onset of canyon incision therefore requires thermochronological tools sensitive to lower temperatures and shorter timescales, such as electron spin resonance (ESR).

Here, we focus on Zion Canyon, an emblematic and well-studied canyon on the western margin of the Colorado Plateau, to evaluate the potential of ESR thermochronology to resolve late Cenozoic to Quaternary exhumation/incision histories. Classical low-temperature thermochronometers suggest that exhumation began around 7 Ma. This exhumation signal integrates regional plateau denudation and canyon incision, preventing the isolation of incision-specific dynamics. In contrast, independent geomorphic constraints document significantly higher incision rates over the last ~1 Myr, implying temporal variations in incision that cannot be resolved with classical thermochronology.

We apply ESR thermochronology to a bedrock elevation profile from Zion Canyon to (i) quantify Quaternary incision rates and (ii) test for changes in cooling rates associated with canyon incision. Preliminary ESR results reveal an increase in cooling rates at ~3–2 Ma, suggesting an acceleration of incision during the late Pliocene–early Pleistocene. These results highlight the potential of ESR thermochronology to bridge the temporal gap between geomorphological constraints and classical thermochronology, and to provide new quantitative constraints on the timing and rates of canyon incision across the Colorado Plateau. In addition, preliminary data from the Grand Canyon (where the incision history is particularly complex and controversial) suggest that ESR signals are not saturated, highlighting the method’s potential to resolve cooling and exhumation over the last few million years in other canyons.