Thermochronological record of slab flattening and roll-back in the eastern part of the Colorado Plateau

The influence of deep-seated processes on tectonics and magmatism has been documented at large scale in different orogens, such as the American Cordilleras. Understanding how these processes shape orogens through time is essential to disentangle their interactions with climatically-driven surface processes. The Colorado Plateau experienced a complex Cenozoic uplift and exhumation history, yet the drivers, magnitude and timing of the successive exhumation phases, as well as their role in conditioning late-stage canyon incision, remain strongly debated. In particular, the legacy of Farallon slab subduction, through slab flattening, subsequent rollback, and associated uplift from combined tectonics, magmatism, and dynamic topography, may have fundamentally structured the plateau prior to more recent canyon incision.

We combine apatite (U–Th–Sm)/He dating with apatite fission-track analysis from bedrock samples collected along an elevation profile in the Black Canyon of the Gunnison (eastern Colorado Plateau). By integrating these thermochronological data with the timing of regional erosional unconformities, we provide new constraints on the Cenozoic thermal evolution of basement rocks in this area. Our results reveal an early cooling phase between ca. 70 and 60 Ma. This phase is followed by reheating between ca. 35 and 30 Ma, corresponding to a temperature increase of ~40 °C, and by a subsequent cooling phase from 30 to 25 Ma of similar magnitude. A final cooling phase occurring after ~5 Ma is required to reach present-day surface temperatures. We interpret the early cooling phase as exhumation related to Laramide deformation associated with Farallon slab flattening. The reheating phase is contemporaneous with a widespread mid-Cenozoic magmatic flare-up interpreted to reflect slab rollback processes. The reheating may be specifically associated with a regional increase in the geothermal gradient or burial beneath volcanic sequences, or a combination of both. The final cooling phase is attributed to Plio-Quaternary incision of the Black Canyon, which generated ~800 m of relief.

Together, these results highlight how the sequence of slab flattening and subsequent rollback exerted a first-order control on Colorado Plateau surface uplift, exhumation and magmatism, thereby preconditioning the landscape on which Plio-Quaternary canyon incision developed. These thermochronological data will be integrated with existing thermochronological datasets to assess at larger scale the spatio-temporal variability of exhumation and reheating in response to changes in the geometry of the downgoing slab.