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Apatite 4He/3He and (U-Th)/He Evidence for an Ancient Grand Canyon

Science  29 Nov 2012:
pp.
DOI: 10.1126/science.1229390

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Abstract

Grand Canyon is one of the most dramatic features on Earth, yet when and why it was carved have been controversial for more than 150 years. We present apatite 4He/3He thermochronometry data from Grand Canyon basement that tightly constrain the near-surface cooling history associated with canyon incision. 4He/3He spectra for eastern Grand Canyon apatites of differing He date, radiation damage, and U-Th zonation yield a self-consistent cooling history that substantially validates the He diffusion kinetic model applied here. Similar data for western Grand Canyon provide evidence that it was excavated to within a few hundred meters of modern depths by ~70 million years ago (Ma), in contrast to the conventional model in which the entire canyon was carved since 5 to 6 Ma.

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