Single-crystal (U-Th)/He dating of 32 apatite and zircon crystals from an impact breccia yielded a weighted mean age of 663 ± 28 ka (n = 3; 4.2 % 2σ uncertainties) for the Monturaqui impact structure, Chile. This ~350 m diameter simple crater preserves a small volume of impactite consisting of polymict breccias that are dominated by reworked target rock clasts. The small size, young age and limited availability of melt material for traditional geochronological techniques made Monturaqui a good test to define the lower limits of the (U-Th)/He system to successfully date impact events. Numerical modeling of ⁴He loss in apatite and zircon crystals shows that, for even small craters such as Monturaqui, the short-lived compressional stage and shock metamorphic stage can account for the observed partial to full resetting of (U-Th)/He ages in accessory minerals. Despite the distinctly different ⁴He diffusion parameters of apatite and zircon, the 2σ-overlapping youngest ages are recorded in both populations of minerals, which supports the inference that the weighted mean of the youngest (U-Th)/He population is the age of formation of this impact structure.

来自撞击角砾岩的 32 颗磷灰石和锆石晶体的单晶 (U-Th)/He 测年得出智利 Monturaqui 撞击结构的加权平均年龄为 663 ± 28 ka（n = 3；4.2 % 2σ 不确定性）。这个直径约 350 米的简单陨石坑保留了少量撞击岩，由多晶角砾岩组成，这些角砾岩以重新加工的目标岩屑为主。用于传统地质年代学技术的熔体材料体积小、年龄年轻和有限的可用性使 Monturaqui 成为确定 (U-Th)/He 系统下限以成功确定撞击事件日期的一个很好的测试。^4的数值建模磷灰石和锆石晶体中的 He 损失表明，即使是像 Monturaqui 这样的小陨石坑，短暂的压缩阶段和冲击变质阶段也可以解释所观察到的 (U-Th)/He 年龄在副矿物中部分到完全重置。尽管磷灰石和锆石的⁴ He 扩散参数明显不同，但在两个矿物群中都记录了 2σ 重叠的最年轻年龄，这支持了最年轻 (U-Th)/He 群的加权平均值是这种冲击结构的形成。