Thermochronology

Thermochronology is a geochronologic technique that provides constraints on possible time-temperature histories of rocks. Thermochronometers comprise combinations of a parent-daughter decay system, a host mineral or phase, and an experimentally determined kinetic model of the dependence of daughter-product loss on time and temperature. Daughter products may be physical manifestations of radioactive decay such as damage zones in crystal lattices or trapped charges, or radiogenic nuclides such as 4He, 40Ar, or 206Pb. Thermochronologic analyses may involve characterization of dose/damage relationships or parent-daughter nuclide ratio in samples. Analyses such as step-heating age spectra that yield concentration profiles within diffusion domains or relative concentrations of domains with differing sizes can be interpreted to constrain finite time-temperature histories, whereas those characterizing bulk properties are typically used to provide point-wise constraints on thermal paths. Thermochronologic measurements are often combined with geologic information to provide interpretations associated with closure or resetting events, or partial retention histories. Thermal histories derived from thermochronology are often combined with models of crustal thermal fields to deduce geologic histories such as spatial-temporal patterns of exhumation.