New Mexico Geological Society Annual Spring Meeting — Abstracts

Evidence from the Colorado and Green River systems of the Colorado Plateau suggests that neotectonic mantle flow has driven 500-1000 m of epeirogenic surface uplift and long wavelength surface deformation (tilting and warping) over the last 10 Ma. This amounts to 25-50% of the current elevation of the region. Evidence includes: 1) the correspondence of low seismic velocity mantle with: atypically high (and rough) topography, steep normalized river segments, and areas of greatest river incision in the Grand Canyon and Colorado Rocky Mountains; 2) higher incision rates and magnitudes in in the upper Colorado River system relative to the Green River, 3) thermochronologic and geologic data showing a significant increase in regional exhumation rate starting 6- 10 Ma; 4) basalt Nd compositions in the western Colorado Plateau that change from lithospheric to asthenospheric during the last 10 Ma; and 5) mantle 3He degassing concentrated in CO2-rich springs overlying low velocity domains. These lines of evidence support convective flow in the last 10 Ma at both whole- and upper-mantle scales, and at >1000 km from the plate margin. The provocative correspondence between mantle anomalies and differential incision of continental-scale rivers offers a promising method for interpreting mantle-to-surface interactions in orogenic plateaus within continental interiors.