Effects of exhumation kinematics and topographic evolution on detrital thermochronometer data

Abstract

Detrital thermochronometer data collected from modern rivers or sedimentary basins have the potential to record the evolution of topographic relief, fault kinematics and erosion within drainage basins. However, few studies have addressed the effects of these different factors on detrital thermochronometer age distributions. Here we use transient 3‐D thermokinematic and landform evolution models to simulate the effects of time‐varying topography and fault kinematics on the thermal field through which detrital samples cool. Cooling‐rate‐dependent apatite (U‐Th)/He (AHe), zircon fission track and muscovite 40Ar/39Ar (MAr) grain age distributions are predicted for samples collected from modern river and basin sediments. These distributions are interpreted to determine the sensitivity of different thermochronometer systems to denudation and deformation histories in drainage basins of varying size. We find that detrital thermochronometers in rapidly eroding regions have a strong sensitivity to the kinematics of exhumation, but lack sensitivity to changes in topographic relief under most conditions. In addition, we find potential for significant overestimation of denudation rates derived from conventional 1‐D age‐elevation relationships as compared to 3‐D model‐prescribed rates. At rapid (∼2.5 mm/y) model‐prescribed denudation rates, 1‐D techniques predict rates that are ∼5 and ∼2 times greater than the 3‐D model rate for the AHe and MAr systems, respectively. In models that explore age distributions in foreland basin sediments, we confirm that the lag time concept is a useful and reliable means for identifying denudation rate changes as no significant change in lag time occurs for changing topographic relief scenarios.