HR: 0800h
AN: T11C-0723    [Abstracts]
TI: Mechanisms of Topographic Uplift for the Southern Rocky Mountains
AU: * Coblentz, D D
EM: coblentz@lanl.gov
AF: Los Alamos National Lab, MS F665, Los Alamos, NM 87545, United States
AU: van Wijk, J
EM: jolante@lanl.gov
AF: Los Alamos National Lab, MS F665, Los Alamos, NM 87545, United States
AB: Current research into the timing and dynamics of topographic evolution in the Southern Rockies suggests that the land surface has undergone significant (up to 2 km ) and recent (c. 10Ma) uplift. Lines of evidence supporting this theory include documentation of profound incision along the river gorges draining the area (Colorado, Gunnison, Arkansas), a radial drainage pattern indicative of centralized uplift, and young topographic landscape characterized by high topographic roughness. The geographic focus of this uplift appears to be centered on the Aspen anomaly of central Colorado - an observed upper mantle low velocity domain similar in terms of spatial scale and velocity contrast magnitude to Yellowstone. This anomaly underlies the highest and roughest topography in the Rocky Mountain region and is suggestive that upper mantle processes are driving active tectonic uplift. Recent seismic results from the CD- ROM and La RISTRA experiments have indicated that both active asthenospheric processes and more ancient compositional heterogeneity within the lithosphere are influencing the tectonics of the region. However, while the tectonic nature of the Yellowstone plume has been the focus of a number of recent studies including subsurface imaging of the upper mantle, the nature of the upper mantle beneath the southern Rockies is still poorly understood. This knowledge gap will be rectified by data collected by the recently NSF-funded CREST project that will provide detailed seismic images beneath the Southern Rockies by 2010. Until the availability of such data we are using a twofold geodynamical modeling approach to evaluate the plausibility of a similar tectonic origin for the Aspen anomaly and Yellowstone. First, from an isostatic perspective the estimated crustal thicknesses of 45-50 km in the central Rockies may be insufficient to fully support average elevations of 3-4 km implying a significant mantle contribution to isostatic equilibrium. Secondly, we have used a finite element model (CITCOM) to evaluate the predicted topographic uplift due to a shallow plume impinging on the base of the lithosphere as well as the uplift associated with delamination of the upper mantle. Preliminary results suggest that the observed topography can well be explained by dynamic topography from a small plume or thermal anomaly in the upper mantle and supporting the notion that Aspen and Yellowstone both have origins in the upper mantle. Such a thermal origin for the Aspen Anomaly is further supported by geochemical evidence from hot-springs in the region.
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8110 Continental tectonics: general (0905)
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting