Collaborative Research: The Age of Grand Canyon: Applying New Tests to Resolve the 150-year-old Debate

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Questions about the age of Grand Canyon, framed by John Wesley Powell in the late 1800s, address the tectonic and landscape evolution of the Grand Canyon region and the tectonic events that have shaped it. Recent papers reinvigorate the debate, and support models for both "old" (70-17 million years) and "young" (5-6 million years) carving of Grand Canyon, with corresponding tectonic models for "old" versus "young" uplift of the Colorado Plateau. Studies supporting the "old" canyon model suggest that an 80-70 million year old east-flowing river, then a 55-30 million year old west-flowing river, incised a canyon in the same location and to nearly the same depth as modern Grand Canyon. In this model, the Colorado River did not play a significant role in excavating Grand Canyon, and the preponderance of tectonic uplift of the Colorado Plateau took place about 70 million years ago. In contrast, "young" canyon models suggest that most of the Grand Canyon has been carved in the last 6 million years once the Colorado River became integrated from the Rocky Mountains to the Gulf of California and that uplift of the Colorado Plateau region has taken place in multiple episodes and may be ongoing due to regional mantle upwelling. This project tests a "paleocanyon resolution" for the Grand Canyon debate in which there are 3 "young" segments, 1 "old" segment, and 1 "intermediate" age segment that collectively provide a record of a complex multi-stage tectonic uplift history for the southwestern U.S. Two complementary methods are used to test this hypothesis. First, apatite triple dating (fission track, (U-Th)/He dating, and 4He/3He analyses) are applied to new samples from each segment to reconstruct cooling paths for rocks and decipher past (now-eroded) landscapes and fault displacements. Second, detrital zircon and sanidine dating of key preserved paleoriver remnants provide essential ground truth to calibrate the thermochronological investigations.The project?s broader significance and importance are enhanced by intense national and international public interest in the Grand Canyon region as one of Earth?s iconic geologic features. The results of this project may change the current paradigm for the incision age of the Grand Canyon. Discussion and resolution of the century-long Grand Canyon debate illustrates the scientific method and progress of science. The project will have significant impacts on student training, increased diversity of the geoscience workforce, outreach to Native American tribes in the region, public informal science education, and increased collaborative progress among diverse geosciences communities.