CENOZOIC UPLIFT ASSOCIATED WITH THE ASPEN ANOMALY, CENTRAL COLORADO, AND UPDATE ON THE CREST COLORADO ROCKIES EXPERIMENT AND SEISMIC TRANSECTS

The Aspen Anomaly of central Colorado is a low velocity mantle anomaly similar in scale to the Yellowstone Park anomaly. It is characterized by sharp velocity transitions and underlies Colorado's highest topography. The CREST experiment involves: 1) mantle-scale seismic imaging using 60 3-D passive IRIS PASSCAL-supported stations (siting in 2007; installation in 2008) coordinated with 18 concurrent embedded EarthScope USArray stations; 2) geologic and thermochronologic studies of the uplift history of the Colorado Rockies; 3) studies of mantle to surface interconnections via mantle degassing, hydrochemistry, and neotectonics. Lowest mantle velocities coincide with the intersection of the NE-trending Proterozoic Colorado mineral belt and the NNW-trending extension of the Rio Grande rift (Fig. 2), suggesting a geodynamic process in which Cenozoic and still-active asthenospheric upwelling and uplift are influenced by Proterozoic lithospheric heterogeneity. Time-space correlations between Cenozoic rock uplift and denudation patterns, magmatism, modern hydrothermal systems, and the modern-day mantle anomaly indicate that the Aspen anomaly may have been tectonically active at several times in the Cenozoic. Magmatism in central Colorado has been episodic, and includes Laramide volcanism of the Colorado mineral belt, Yellowstone-sized volumes of Oligocene volcanics near the anomaly (San Juan volcanic field) and 25-0 Ma basaltic magmatism at the edges of the anomaly. The highest peaks of the Colorado Rockies are located above the mantle anomaly and major drainage is radial away from the anomaly suggesting broad mantle-driven epeirogenic surface uplift. Apatite fission track data from the MWX well on the edge of the anomaly indicates the initiation of rapid exhumation at ~6 Ma, perhaps related to Neogene uplift. Mantle degassing and high heat flow through hot springs and CO2 springs indicate continued mantle devolatilization. Highest 3He/4He values are up to 2.17 Ra (~0.25 of MORB) at Poncha Pass at the north end of the Rio Grande rift, and mantle 3He/4He values ranging between 0.1 and 2.17 Ra are detected in almost all the hot springs in Colorado. Aqueous geochemical modeling indicate significant flux of mantle-derived CO2 (109 to 1010 mol C/yr). Emerging data offer potential for understanding ongoing mantle-to-surface interconnections.