Paper No. 3
Presentation Time: 8:45 AM
MANTLE DRIVEN UPLIFT OF THE ROCKY MOUNTAIN/ COLORADO PLATEAU REGION, ITS SURFACE MANIFESTATIONS, AND IMPLICATIONS FOR MANTLE PROCESSES
The Rocky Mountain (RM)/ Colorado Plateau (CP) region is emerging (literally) as a globally important region to test and resolve debates about the processes by which continental lithosphere is modified by interactions with asthenosphere, and the expected surface responses to mantle dynamics at multiple scales. A first-order observation from mantle tomographic images is a dramatic lateral seismic velocity heterogeneity in this region, with lateral P-velocity gradients near 100 km depths showing ~6% Vp variations over <80 km lateral length-scales that require significant thermal (up to 500 °C) and partial melt/ rheology variations sufficient to drive mantle convective flow. Important negative anomalies in the RM are termed the Front Range, Aspen, San Juan and Jemez anomalies. On the southwestern CP, we focus on the high velocity (in P and S waves) anomaly that we call the Escalante Anomaly and its sharp gradients with low velocity domains that rim the western CP. Accumulating evidence for mantle-driven surface deformation and mantle-to-surface connections at a variety of spatial and temporal scales are as follows. 1) Thermochronometric data indicate regional uplift episodes (Laramide 75-50 Ma; mid Tertiary 35-15 Ma, Neogene < 10 Ma) separated by times of slow cooling potentially indicating episodic mantle tectonism. 2) Correlations between high topography, low velocity mantle and thin crust beneath the RM favor delamination models during and following the mid-Miocene ignimbrite flare up. 3) Inward sweep of asthenosphere-derived basalt (last 25 Ma) around the CP indicates melt transfer in zones of high velocity gradients and propagation of these zones at plate tectonic rates. 4) Tilting of basalt-capped and beveled fluvial paleosurfaces indicate Miocene and ongoing epeirogenic warping of the western Great Plains, 5) Differential post- 10 Ma incision rates along the continental-scale Colorado River (CR) indicate uplift of the RM relative to the CP and the CP relative to the Basin and Range. 6) Regional correlations showing steeper normalized river channels (and rougher topography) associated with low mantle velocity mantle and/or steep velocity gradients. 8) Hydrologic studies show domains of mantle CO2 and 3He degassing correlate with low velocity domains and process zones.