AGE AND CARVING OF GRAND CANYON: TOWARDS A RESOLUTION OF 150 YEARS OF DEBATE

A GSA- and NSF-sponsored 280-mile field conference was conducted September 14-18, 2019, by raft through the Grand Canyon. The age and evolution of the 1.6-km-deep, 270-mile-long Grand Canyon have been debated since J.W. Powell’s exploration of the Colorado River in 1869. This GSA Thompson Field Forum, 150 years after Powell’s trip, involved 28 researchers, young scientists, and students who discussed the evidence for the age and incision history of Grand Canyon in the context of recent advances and ongoing debates. A continued objective is to promote a next generation of research on the evolution and tectonic geomorphology of this iconic region, as well as similar studies globally, and debate the evidence for and against mantle-driven influences that shape topography. The field forum included key outcrop discussions for incision data, neotectonics, and lava dam studies. Geodynamics discussions involved the relative importance of mantle buoyancy structure (isostatic support) and mantle flow (dynamic support) for understanding the uplift history of the Colorado Plateau–Rocky Mountain region. Thermochronologic data for now-eroded paleocanyons and landscapes provided important, and still debated, new constraints on landscape evolution. Geomorphologic discussions included landscape modeling, bedrock strength controls on river and canyon morphology, and evidence for steady versus transient incision. This research has global reverberations in terms of Cenozoic neotectonics, landscape evolution, and mantle influence on surface topography. The objective of this panel discussion is for conveners and participants to give short summaries of progress made during the field forum and to stimulate next steps on these topics.