Late Miocene rejuvenation of central Idaho landscape evolution: A case for surface processes driven by plume-lithosphere interaction

We utilized field measurements of erosion rates and topographic analyses to constrain the timing and magnitude of landscape rejuvenation on the western flank of the Rocky Mountains in central Idaho, United States. Deeply incised canyons of the Clearwater, Salmon, and Snake Rivers dissect a broad region of roughly 8 × 10$^4$ km$^2$. Along the Salmon River, an observable break in slope separates relict landscapes of low relief (<400 m valley depth) from high-relief landscapes (1200–1600 m valley depth) adjusting to base-level forcing. The $^{10}$Be cosmogenic radionuclide concentrations in river sediment record basinwide erosion rates that increase from 0.05 mm/yr ± 0.008 in the low-relief topography to 0.12 mm/yr ± 0.016 in the adjusting, high-relief landscapes over the last 10$^3$–10$^4$ yr and are consistent with longer-term estimates of erosion. Using the covariance of erosion rates and channel morphology, we calibrated a 1-dimensional river incision model to constrain the dynamics of incision along the Salmon River. More than 10$^5$ model runs explored uncertainty and assumptions and found that increased incision initiated roughly 9.5 ± 2 Ma and persists to the present. New constraints on the distribution of erosion processes at locations within a 400 km transect across central Idaho suggest northward surface tilting. In light of these data, we offer a new hypothesis that attributes late Miocene landscape rejuvenation of central Idaho to surface uplift driven by density changes in the mantle-lithosphere precipitated by the Yellowstone plume. We demonstrated the hypothesis through a simple model of flexure of an elastic plate subject to a buried buoyant load, and we found that density changes extending 200 km north of the Snake River Plain can reproduce the south-north distribution of uplift with reasonable values for elastic thickness and anomalous density.

Publication Date:
Oct 12 2018
Date Submitted:
Jun 28 2019
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 Record created 2019-06-28, last modified 2019-07-11

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