RECONCILING THERMOCHRONOMETRIC EVIDENCE FOR GRAND CANYON INCISION: PRELIMINARY RESULTS

Recent thermochronometric evidence for an ancient (~70 Ma) Grand Canyon has sparked considerable debate in the literature, where incision ages range between 70 and 5 Ma. Much of this debate is due to the conflicting conclusions drawn from different thermochronometric datasets with different ranges of temperature sensitivity. In particular, 4He/3He data, sensitive to 80-30°C, from the Western Grand Canyon require relatively rapid cooling at 70 Ma and long periods of time at near to surface temperatures (Flowers and Farley, 2012, Science 338). In contrast, combined analysis of apatite fission track (AFT) and (U-Th)/He data, with a total temperature sensitivity of 120-50°C, suggest that rocks resided at ~50°C until approximately 6 Ma (Lee et al., 2013, Geosphere 9). Reconciling these differences is central to our understanding of the development of the Grand Canyon and, thus, landscape evolution and uplift of the Colorado Plateau. A range of ideas can be proposed to explain this discrepancy: unknown helium diffusion kinetics; anomalous fission track annealing; or differences in resolution of the inferred time temperature paths. In addition, converting time temperature paths to exhumation rate, or incision rate, requires making assumptions about the thermal structure of the crust. Here, we present preliminary attempts to evaluate the potential of the different datasets to resolve time temperature histories. 3-D thermo-kinematic models, which account for advection and diffusion of crustal temperature below evolving topography, are used to generate time temperature paths and thus synthetic data. The analysis of the synthetic data allows us to explore model resolution and test sensitivity to various assumptions.