Tectonic controls of Holocene erosion in a glaciated orogen

Abstract

Abstract. Recent work has highlighted a strong, worldwide, glacial impact of orogen erosion rates over the last 2 Ma. While it may be assumed that glaciers increased erosion rates when active, the degree to which past glaciations influence Holocene erosion rates through the adjustment of topography is not known. In this study, we investigate the influence of long-term tectonic and post-glacial topographic controls on erosion in a glaciated orogen, the Olympic Mountains, USA. We present 14 10 new 10 Be and 26 Al analyses which constrain Holocene erosion rates across the Olympic Mountains. Basin-averaged erosion rates scale with basin-averaged values of 5-km local relief, channel steepness, and hillslope angle throughout the range, similar to observations from non-glaciated orogens. These erosion rates are not related to mean annual precipitation or the marked change in Pleistocene alpine glacier size across the range, implying that glacier modification of topography and modern precipitation parameters do not exert strong controls on these rates. Rather, we find that despite intense spatial variations in 15 glacial modification of topography, patterns of recent erosion are similar to those from estimates of long-term tectonic rock uplift. This is consistent with a tectonic model where erosion and rock uplift patterns are controlled by the deformation of the Cascadia subduction zone.

Building a Young Mountain Range: Insight Into the Growth of the Greater Caucasus Mountains From Detrital Zircon (U‐Th)/He Thermochronology and 10Be Erosion Rates

“…Much of the signal indicative of recent acceleration of erosion/exhumation rate in the western GC comes from bedrock samples taken from areas glaciated during the LGM. In such regions, (a) fluvial landscape form could be obscured or modified by glacial activity (e.g., Anderson et al., 2006; Brocklehurst & Whipple, 2002) and thus the extrapolation of millennial erosion rates from k sn could be problematic and (b) glacial erosion itself could contribute to increased rates of rock uplift (e.g., Hallet et al., 1996), though the extent to which glaciers can perturb long‐term exhumation rates remains controversial (e.g., Adams & Ehlers, 2018; Michel et al., 2018). However, the observed patterns largely persist if formerly glaciated sample sites are removed from consideration, though the fidelity of the patterns are reduced (Figure 8).…”

The influence of upper-plate advance and erosion on overriding plate deformation in orogen syntaxes

“…Bulk velocities are the result of solving the quasi-steady-state force balance equations for nearly incompressible fluids with a finite-element approach on an octree mesh. Pressure values are derived indirectly from the velocity solution by the penalty method (e.g., Bathe, 1982), and local smoothing is applied to avoid smallscale pressure oscillations. Finally, temperature is computed, incorporating the effects of material velocities and thermal properties.…”

“…where µ is the material shear viscosity, V the velocity field, P the pressure, is the density, and g the gravity acceleration. The solution is computed with the finite-element method using Q1P0 elements; i.e., the pressure is calculated from the velocity field by the penalty formulation (e.g., Bathe, 1982):…”