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. Copyright 2007 by the American Geophysical Union.