Physical Sciences and Mathematics Commons^™

Landscape Evolution Of The Southern Colorado Plateau Using Low-Temperature Apatite Thermochronology And Detrital Zircon And Sanidine Provenance Studies, Carmen L. Winn

Earth and Planetary Sciences ETDs

Chapter 1: Westernmost Grand Canyon

Conflicting hypotheses about the timing of carving of the Grand Canyon involve either a 70 Ma (“old”) or < 6 Ma (“young”) Grand Canyon. This paper evaluates the controversial westernmost segment of the Grand Canyon where the following lines of published evidence firmly favor a “young” Canyon. 1) North-derived Paleocene Hindu Fanglomerate was deposited across the present track of the westernmost Grand Canyon, which therefore was not present at ~55 Ma. 2) The 19 Ma Separation Point basalt is stranded between high relief side canyons feeding the main stem of the Colorado River and was emplaced before these tributaries and the main canyon were incised. 3) Geomorphic constraints indicate that relief generation in tributaries and on plateaus adjacent to the westernmost Grand Canyon took place after 17 Ma. 4) The late Miocene-Pliocene Muddy Creek Formation constraint shows that no river carrying far-traveled materials exited at the mouth of the Grand Canyon until after 6 Ma.

Interpretations of previously-published low-temperature thermochronologic data conflict with these lines of evidence, but are reconciled in this paper via the integration of three methods of analyses on the same sample: apatite (U-Th)/He ages (AHe), ⁴He/³He thermochronometry (⁴He/³He), and apatite fission-track ages and lengths (AFT). “HeFTy” software was used to generate time-temperature (t-T) paths that predict all new and published ⁴He/³He, AH, and AFT data to within assumed …