NEWS & EVENTS

The ability to extract exceptionally high-resolution thermal histories from a single crystal using 4He/3He thermochronology has vastly appealing geological implications; however, methodological and analytical challenges have, in part, limited the accessibility in obtaining 4He/3He datasets. These challenges include the requirement to induce uniform and high concentrations of spallation 3He within crystals via proton irradiations, and to (quasi-)simultaneously measure especially low quantities of 3He and 4He during step-heating analysis on individual crystals. Here, we discuss new efforts to advance the accessibility and utility of 4He/3He thermochronology by (1) establishing a new proton irradiation protocol with improved efficiency, (2) assessing apatite 4He/3He systematics via a calibration exercise exploiting the late Oligocene Fish Canyon Tuff (FCT) thermochronology age standard, and (3) developing new tools to assist in the interpretation and application of 4He/3He datasets. First, in collaboration with the Helmholtz Zentrum Berlin (HZB), we have implemented a newly developed in-vacuum and high-flux proton irradiation protocol that limits the time-delay between sample irradiation to 4He/3He analysis down to ~2 weeks, and can be conducted on a monthto-month basis. Furthermore, we reveal how computer simulations emulating the HZB irradiations can be utilized to optimize the geometry and composition of the target assembly to improve the uniformity of 3He induced across all samples. Second, we present new 4He/3He degassing spectra from two distinct FCT sampling localities—the ‘classic’ locality with young reset apatite (U-Th)/He ages, and the distal quarry locality with no apparent post-emplacement reheating. The resulting 4He/3He spectra reveal that the ‘classic’ FCT locality has a notably more diffusive 4He distribution compared to the purely quenched distal FCT locality, which preserves an apparent alpha-ejectiononly 4He/3He spectrum. In addition, the observed consistency in FCT 4He/3He spectra from apatite crystals independently irradiated via HZB and conventional protocols corroborates the robustness of
our newly established HZB protocol. Lastly, we present the progress of ongoing projects implementing apatite 4He/3He thermochronology, and discuss new tools developed to facilitate data interpretation and to inform sampling strategies for 4He/3He-based studies. In sum, these developments provide important new insights intended to advance the future utility of both 4He/3He thermochronology and 3He-based diffusion studies. 

For Additional information: colleps@uni-potsdam.de