UThHe

UThHe, short for uranium-thorium-helium dating, is a radiometric thermochronology method used in geochronology to reconstruct the thermal history of rocks. The technique hinges on the slow accumulation of helium-4 produced by the alpha decay of uranium and thorium contained within minerals. Because helium diffusivity increases with temperature, the amount of helium retained in a mineral records its past temperature history. By measuring helium alongside uranium and thorium concentrations and applying known decay constants, a cooling age or thermal event timing can be inferred.

Common target minerals for UThHe dating include apatite, zircon, and titanite. Apatite is sensitive to relatively low-temperature histories (closure temperatures on the order of tens of degrees Celsius), while zircon and titanite preserve higher-temperature records. UThHe ages are often integrated with other thermochronometers to build comprehensive thermal histories for crustal blocks, documenting processes such as burial, cooling, uplift, and exhumation.

Measurement and interpretation involve releasing helium from the mineral lattice, typically through step-heating or laser-ablation, and quantifying it with noble gas mass spectrometry. U and Th contents are determined by mass spectrometric methods, such as ICP-MS or TIMS. Age calculations require corrections for factors such as alpha-ejection, possible initial helium, and diffusive loss. Uncertainties depend on sample quality and the degree of open-system behavior; well-behaved samples can yield ages with moderate precision, while complex histories may require careful modeling.

UThHe dating complements other low-temperature methods and is widely used to constrain the timing of cooling and metamorphic events, timescales of crustal processes, and the thermal evolution of geological terranes. See also (U-Th)/He dating, apatite fission-track dating, and zircon geochronology for related approaches.