Geodynamic influence on landscape evolution in the northern U.S. cordillera: cosmogenic erosion rates, incision models, and basalt flow ages show canyon incision to be mid- to late Miocene in age

Abstract

Deep canyons along the Salmon and Clearwater Rivers in central Idaho (U.S.) suggest long-lasting transient incision, but the timing and drivers of this incision are not well understood. For example, it is currently unclear how this incision relates to the Yellowstone hotspot, flood basalts, or drainage reorganization events like the drainage of Lake Idaho. Unraveling the drivers of canyon incision here would provide insight into the geologic history of the northern U.S. cordillera. Here, we utilized the in-situ 10Be cosmogenic radionuclide concentrations for 46 samples (17 new) of fluvial sediment from streams across the region. We use these concentrations to quantify erosion rates, calibrate stream power models, and estimate incision timing. We estimate that transient incision along the Salmon River began prior to ~10 Ma, preceding the drainage of Lake Idaho. Canyon age seems to decrease to the north (further from the Yellowstone hotspot track), however. Further north, we estimate the incision of basalt tributaries began prior to ~6 Ma but the age of the basalt itself suggests local incision began after ~11.5 Ma. These age constraints roughly coincide with the passage of the Yellowstone plume through southern Idaho. We argue the Yellowstone plume has contributed to incision by causing lava damming, drainage reorganization, facilitating delamination, and/or driving lower crustal flow. We show that lithology has a significant influence on fluvial erosion (potentially through both erodibility and n), assumptions regarding model parameters like slope exponent n significantly influence results, and geodynamic processes can exert a significant influence on landscape evolution.