OLG: a new potential reference material for apatite (U–Th)/He dating

Abstract

The (U–Th)/He dating technique has been widely applied for constraining shallow crustal geological processes, with apatite being the most commonly used mineral due to its low closure temperature and broad occurrence. Currently available (U–Th)/He reference materials, including Durango, Fish Canyon Tuff (FCT), Limberg t3 Tuff (LT3T), and MK-1, are relatively young (<40 Ma). This highlights the need for a new, homogeneous, and older reference. In this study, we characterize a new apatite sample, OLG, obtained from a mineral dealer and sourced from the Otter Lake area in the Grenville Province, Canada. Single-grain (U–Th)/He dating yields highly reproducible ages of 210.2 ± 1.4 Ma (2σ), significantly older than those of existing reference materials. BSE imaging, EPMA, and LA-ICP-MS analyses confirm its major-element homogeneity and relatively uniform trace-element distribution, although minor inclusions could be present. OLG shows strong U, Th, and He signals, with an average U concentration of ∼112.2 ppm, Th concentration of ∼923.7 ppm, and a Th/U ratio of ∼8.2. Its older age, high U and Th concentrations, and excellent compositional homogeneity indicate that OLG could serve as a robust new reference material for high-precision (U–Th)/He thermochronology.