Geology

How Old Is the Canyon?

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Science  16 Nov 2007:
Vol. 318, Issue 5853, pp. 1039
DOI: 10.1126/science.318.5853.1039a

Much about the timing of formation of the Grand Canyon in Arizona remains uncertain. The process is closely tied into the history of uplift of Western North America during the Cenozoic, including even recently, as well as regional climate change. One approach toward improved understanding is to date past positions of the Colorado River as it deepened the canyon. To do this, Karlstrom et al. have taken advantage of the many volcanic fields in the western part of the canyon; some of these poured lava into the canyon during the past several million years. In fortunate cases, remnants of these flows are preserved perched on ledges or beaches in the canyon, marking past river levels. 40Ar/39Ar dating of these young flows shows that the western part of the canyon has continued to deepen by about 100 to 150 m since about 1.5 million years ago. To the east, across a major fault, the canyon has been deepening at 2 to 3 times that rate. Further dates show that this pattern of active differential uplift, facilitated by faulting, has operated over the past 5 to 6 million years and has continued to modify the canyon even geologically recently. — BH

Geol. Soc. Am. Bull. 119, 1283 (2007).

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