Carving Grand Canyon: Resolving 150 Years of Debate

In 1869, Major John Wesley Powell led an expedition down the Colorado River through the Grand Canyon and other deeply incised landscapes of the Colorado Plateau, leading him to propose that the drainage system was antecedent to the prevalent monoclines of the region. Two decades later, his successors Charles Walcott and William Morris Davis concluded instead that the river was superimposed upon the structures, sparking a debate that would last over a century about when the Grand Canyon was incised and the relative timing of uplifts and canyons. Today, tools such as low temperature thermochronology combined with better geochronologic constraints provide a refined view of when this iconic landscape formed, but disagreement remains. Recent competing hypotheses for the age of the Grand Canyon involve a “young” canyon carved predominantly by the Colorado River since 5-6 Ma or an “old” canyon of 55-70 Ma later re-used by the Colorado River.

The current resolution of this debate is that sections of the Grand Canyon were partially carved by drainages at ~55-70 Ma and 25-15 Ma, and the remainder was carved when the Colorado River became integrated through these older segments in the past 5-6 Ma. However, the westernmost section has remained controversial. In this reach, geologic data have favored young incision while interpretations of thermochronologic data have been at odds, with different studies arguing for a 55-70 Ma section or a 5-6 Ma section. My research has resolved this debate by applying multiple apatite thermochronometers, including high precision 4He/3He diffusion data, and integrating geologic constraints. This supports 5-6 Ma incision along this reach of the river and also provides a cautionary tale about assumptions involved in inverse modeling of thermal histories for samples with a complex burial reheating history.

Speaker
Carmen Winn

I am finishing my Ph.D. in Earth and Planetary Sciences from the University of New Mexico (July, 2018) after completing a B.S. in Geology from Northern Arizona University in 2012. I study landscape evolution and neotectonics using low-temperature apatite thermochronology data combined with geologic constraints, including detrital zircon and detrital sanidine geochronology. I am looking for a postdoctoral scholar position studying young tectonics and landscape evolution and hope to broaden my experience with computational tools and big datasets. When not at my computer analyzing data and writing, I enjoy spending time outside, running rivers and climbing mountains.

Venue

Room: 
314/315, level 3, Steele building (#3)