This project is a follow up to a series of previous CD funded Rocky Mountain focused projects building on the discovery of a low velocity anomaly in the mantle beneath central Colorado. The proposed project involves a wide variety of techniques assembled to address the cause of the so called "Aspen anomaly", its history, and its effect on crustal evolution. The PIs are interested in the connection between changes in the mantle causing modification of surface topography. They have observed that the Aspen anomaly is located beneath the highest portion of the Rocky Mountains. They equate low mantle seismic velocities with low mantle densities to cause uplift. They will investigate whether the very large velocity variations in the mantle beneath this area are: a) in the lithosphere or asthenosphere, b) reflect Proterozoic lithospheric sutures reactivated by Cenozoic tectonism, c) are caused by a plume, and d) are caused by the presence of melt. These are all important and relevant questions for Continental Dynamics.
Specifically, the PIs will use: - passive seismology to better define the anomaly using tomography, receiver functions, surface waves, and anisotrophy; - geological studies (magmatic history, low temperature thermochronology, tectonic geomorphology) to identify Cenozoic tectonic and magmatic history to define long term and current history; - geodynamical models of topography uplift and mantle processes to study their connection.
The intellectual merit of the CREST experiment (Colorado Rockies Experiment and seismic Transects) was to develop and test a hypothesis that uplift of the Rocky Mountains and Colorado Plateau regions is actively happening, is being driven by upwelling buoyant mantle, and that we can measure surface responses in today’s mountains, rivers and canyons to these deep mantle driving forces. The experiment provided exceptionally high resolution images of globally-large seismic velocity anomalies in the crust and mantle, and showed that low velocity upwelling zones are directly underneath regions with atypically high (and rough) topography, steep river gradients, areas of greatest river incision, and areas where input of deep fluids into hot and cool springs is degrading groundwater quality. Our thermochronologic and geologic data show that uplift and surface erosion accelerated starting 6-10 million years ago, especially in these regions directly above the imaged low velocity, upwelling, mantle. We concluded that surface uplift on the order of 500-1000 m in the last 10 million years helps account for about half of the current high elevation of the Rockies, with the rest achieved during earlier uplift events. Broader impacts of this work included our inclusive, open data access, collaborative, multidisciplinary research approach, training of numerous graduate and undergraduate students into the workforce, and appearances on public television and informal science education exhibits for the public. Scientifically, we provided strong momentum for models that North Americas surface topography are actively and dynamically responding to deep Earth mantle dynamics as now increasingly better imaged by our project and the EarthScope Experiment. Outcomes of the UNM portion of the award (2006-2012) included about 22 articles in peer reviewed journals, training of 3 Masters and 2 PhD graduate students (including one Hispanic and one Native American student), mentoring of about 8 undergraduate part-time researchers, and presentation of about 24 papers and presentations (many by student authors) at national geological and geophysical meetings. Public outreach appearances were on the History Channel, National Geographic Channel, Discovery Channel, Grand Canyon National Park Visitor’s Center movie, and KNME Albuquerque public television. All these appearances attempted to provide public audiences with new information and excitement about the ongoing active uplift of the western US region, its importance for understanding landscapes and water quality, and the important interconnections between Earth systems and human societies.
