Low-temperature thermochronology: Resolving geotherm shapes or denudation histories?

Thermal histories derived from apatite fission-track data are remarkably consistent irrespective of tectonic setting and overall rate of cooling. Rapid cooling through the partial annealing zone is typically followed by slower cooling, and such histories can only be explained by systematic errors in the experimentally derived annealing rates used to determine the thermal histories, or a consistent geotherm shape characterized by a relatively low geothermal gradient in the uppermost crust. Differences between the cooling paths characterizing individual tectonic settings indicate that geotherm shape influences the cooling histories. This suggests that crustal geotherms, especially those in orogenic belts, are characterized by a shallow zone of high permeability, allowing the rapid transfer of heat by fluid advection, perhaps together with a near-surface zone affected by enhanced heat loss due to topographic effects. The influence of such controls on cooling histories must be considered prior to using thermochronology data to constrain denudation histories.