Late Miocene exhumation and uplift of the Washington Cascade Range

Abstract

The Washington Cascade Range is a complex, polygenetic mountain range that dominates the topographic, climatic, and cultural configurations of Washington State. Although it has been the locus of ongoing arc magmatism since the Eocene, most of the range is distinct from the southern part of the arc in Oregon and California in that bedrock uplift has produced high surface elevations and topographic relief, rather than volcanic burial or edifice construction. (U-Th)/He and fission-track ages of bedrock samples on the east flank of the range record relatively rapid cooling in the early Tertiary, but slow exhumation rates (ϳ0.2 km/m.y.) through most of the Oligocene. Samples on the west flank suggest rapid cooling in the late Miocene (8-12 Ma), and age variations in vertical transects are consistent with a pulse of rapid exhumation (0.5-1.0 km/m.y.) at that time. Apatite He ages as young as 1-5 Ma in several areas suggest that high cooling and possibly exhumation rates persist locally. Accelerated exhumation rates ca. 10 Ma are also observed in the Coast Mountains of British Columbia and southeast Alaska, ϳ1500 km to the north, suggesting a large-scale mechanism for the exhumation pulse at that time.

Mudflow Disturbance in Latest Miocene Forests in Lewis County, Washington

“…Coincident with this change in type of volcanism was the formation of a regional northwest-southeast fold system in Washington (Cheney and Hayman, 2007). This was followed by north-south-aligned Cascades uplift that varied from high uplift in the northern Washington Cascades to low uplift in the southern Washington Cascades, and by faulting that is similar in style to Basin and Range deformation (Reiners et al, 2002;Cheney and Hayman, 2007). These volcanic and structural events created a divide between western Washington and central and eastern Washington that shaped the depositional basins of the region.…”

“…A return to summer-dry climates occurred during further cooling associated with the advent of glaciation during the Pleistocene. Timing of the uplift and development of an obvious rain shadow in central Washington is based on tectonic and paleobotanical work (Smiley, 1963;Leopold and Denton, 1987;Reiners et al, 2002;Cheney and Hayman, 2007) calibrated with geochronologic dating (Smith, 1988;Smith et al, 1988).…”

Mountain uplift and the glaciation of North America – a sensitivity study

“…2). These studies constitute a regional scale database that indicates a significant acceleration of rock exhumation rates during the Late Miocene (Reiners et al, 2002;Parrish, 1983;O'Sullivan and Parrish, 1995;Fitzgerald et al, 1995;O'Sullivan and Currie, 1996;Farley et al, 2001). On its own such information should be interpreted in terms of surface uplift with caution.…”

“…Finally, low temperature thermochronometric studies have been conducted at numerous places in the western Cordillera from 47 • N to 63 • N (as summarised in Reiners et al, 2002 and references therein; Fig. 2).…”

A hydroclimatological approach to predicting regional landslide probability using Landlab

“…Calibration of the soil evolution model was performed by adjusting model parameters from the literature (e.g., Tucker and Slingerland, 1997;Nicótina et al, 2011) and comparing the mean annual rock erosion rate estimated by the model to long-term average rock erosion rates published for the Cascade Mountains, which range from 0.02 to 0.5 mm yr −1 over roughly the last several Myr (Reiners et al, 2002(Reiners et al, , 2003 and slightly higher rates over the last millennia of 0.08 to 0.57 mm yr −1 (Moon et al, 2011). In addition to published erosion rates, the resulting soil depths were compared to the SSURGO-SD, which ranged from 0.09 to 2.01 m across NOCA.…”