Effect of Alpine glaciation on thermochronometer age‐elevation profiles

Abstract

Low‐temperature thermochronometers are widely used to quantify exhumation histories, typically by interpreting sample cooling age‐elevation relationships. However, the effects of specific geomorphic processes on age‐elevation profiles are seldom considered. We integrate apatite (U‐Th)/He [AHe], apatite fission track, and zircon (U‐Th)/He thermochronometry with numerical modeling to determine the effect of glacial erosion on an age‐elevation profile from the heavily glaciated southern Coast Mountains, British Columbia. AHe data show a distinct break in slope in age‐elevation between 1900–2100 m. We interpret this break in slope as an acceleration of erosion associated with the onset of alpine glaciation. We use a 3‐D thermo‐kinematic model to constrain pre‐ and synglacial erosion rates. Results indicate a preglacial erosion rate of ∼0.4 mm/yr that accelerated by a factor of ∼2 since ∼6 Ma. We propose that glacial valley widening and deepening are responsible for the observed nonlinear AHe age‐elevation profile.