This project will study how the Grand Canyon region is responding to surface uplift driven by upper mantle convection. The goal of the research is to use the continental-scale Colorado River system as a well exposed field laboratory and sensitive gauge of the complex interplay between the processes of faulting, volcanism, uplift, river dynamics, and climatic processes that, collectively, are shaping the landscape of this classic region. The methods and approaches to be used include a variety of dating techniques (Ar-Ar dating of basalt flows, U-series dating of travertine cements, cosmogenic ages of gravels, OSL dates on young terraces) that will be used to determine terrace gravel ages. These deposits preserve past landscape positions and hence can be used to gauge uplift, incision rates, and changing landscapes. The aim is to test the idea that mantle flow and buoyancy modification are driving surface uplift and long wavelength surface deformation of the Colorado Plateau by determining whether or not there are spatial patterns in incision rate that mimic mantle anomalies.
This research will test the idea that the rugged topography of the Grand Canyon and western United States are being re-shaped today by upper mantle convection. This movement of mass and fluid is taking place hundreds of kilometers below the surface and involves upwelling domains of hot buoyant asthenosphere that consists of flowing rock, partial melt, and fluid, as well as downwelling domains of cold dense North American lithosphere. The upwellings appear to be responsible for 400-1000 meters of surface uplift that has taken place in the Colorado Plateau region in the last 10 million years. This amounts to 25-50% of the present average elevation of the region. This uplift is still ongoing. The research plan involves integration of teaching with research and mentorship of numerous graduate and undergraduate students, including Hispanic and Native American students from the southwestern U.S.. The project will lead to improved written and web materials on Colorado Plateau uplift and canyon carving that will be linked to geoscience interpretation for Plateau Parks via the National Park Service web pages and the newly opened Trail of Time Geoscience Education Exhibition at Grand Canyon National Park.
Overview: This study has utilized the iconic landscapes of the southwestern US, including the Grand Canyon – Colorado Plateau region, as a field laboratory to understand connections between the Earth’s mantle and surface processes of landscape evolution and river incision. Intellectual Merit: We have shown that ongoing flow of Earth’s mantle beneath the western Colorado Plateau has and is driving tilting and warping of the Colorado Plateau-Rocky Mountain region over the last 10 Ma. This hypothesis was tested by analyzing the incision history of the Colorado River system. Mantle influences on the surface also include migration of surface volcanism. An unanticipated advance, catalyzed by our recent data and community interactions, is that we have proposed a potential solution to the 140-year-long scientific debate about the age of the Grand Canyon. It is neither "old" (70 million years old), nor "young" (< 6 million years). Instead, our 2014 Nature Geoscience paper suggests Grand Canyon is composed of an "old" segment, an "intermediate" age (25-15 Ma) segment, and 3 "young" segments that were linked together during integration Colorado River 5-6 million years ago. This new hypothesis proposes that most of Grand Canyon has been excavated by the Colorado River in the last 6 million years, but that its landscape evolution has a rich precursor history. Broader Impacts: Specific accomplishments were as follows. 1) We are working on written materials for geoscience interpretation for Plateau Parks, to reach its >5 million annual visitors with up-to-date results from NSF-funded research; 2) We have published open access databases for river incision rates, basalt ages, and landscape cooling histories derived from thermochronology; 3) Our student training effort has involved 7 graduate and 3 undergraduate student, including four minority graduate students and 1 minority undergraduate student; these students are all successfully completed and on their paths to the geosciences workforce or the professoriate. 4) Our work generated extensive and positive media attention that has made the geosciences more visible and understandable to the American public and shown how the scientific method can be applied to questions of great public interest. A transformative outcome of this project has been the forging of a large multi-disciplinary geoscience community effort to resolve long-standing debates about the landscape evolution of the Colorado Plateau region. We have catalyzed research advances by convening and organizing a special Geosphere Themed Issue on Colorado River evolution (Karlstrom and Aslan as Guest Associate Editors) that had 4 papers published in 2012, 7 papers in 2013, 12 papers so far in 2014, and another 11 papers for late 2014 and early 2015. The total volume, by early 2015, will thus have 34 papers (15 by us and our students) that, collectively, have revolutionized our understanding of the landscape evolution of the southwestern US. Additional papers have also appeared in peer- reviewed journals and been presented at National meetings. 15 of our 25 published papers, and 46 of the 54 presentations at meetings involved student coauthors which represents a significant accomplishment of our student mentoring program.
