Screening apatites for (U-Th)/He thermochronometry via continuous ramped heating: He age components and implications for age dispersion

摘要

Old slowly-cooled apatites often yield dispersed (U-Th)/He ages for a variety of reasons, some well understood and some not. Analytical protocols like careful grain selection can reduce the impact of this dispersion but add costs in time and resources and too often have proven insufficient. We assess a new analytical protocol that utilizes static-gas measurement during continuous ramped heating (CRH) as a means to rapidly screen apatite samples. In about the time required for a conventional total-gas analysis, this method can discriminate between samples showing expected volume-diffusion behavior and those showing anomalous release patterns inconsistent with their direct use in thermochronologic applications. This method also appears able to discriminate between the radiogenic and extraneous He-4 fractions released by a sample, potentially allowing ages to be corrected.