Abstract Obtaining accurate and precise apatite fission-track (AFT) ages depends on the availability of high-quality apatite grains from a sample, ideally with high spontaneous fission-track densities (c. >1.105 tracks.cm−2). However, many natural samples, such as bedrock samples from young orogenic belts or low-grade metamorphic samples with low U contents yield low spontaneous fission-track densities. Such apatites must be counted to avoid biasing the resultant FT age. AFT dating employing LA-Q-ICP-MS spot ablation works very well for grains with high spontaneous fission-track densities. This approach allows detection of potential U zoning, while also removing the need for an irradiation step and facilitating simultaneous acquisition of U-Pb and trace element data. The LA-Q-ICP-MS spot ablation thus offers several advantages compared to the External Detector Method (EDM). However, the spot ablation approach requires the counted area to mimic exactly the site and size of the laser spot, which for grains with low spontaneous fission-track densities ( 1.106 track.cm−2) to assess the precision and accuracy of our approach. Most apatite samples investigated here were previously dated by the EDM or the LA-Q-ICP-MS ablation spot method. The AFT grain-mapping ages agree with previously published EDM or LA-Q-ICP-MS spot ablation ages at the 2σ level. For each apatite sample, we simultaneously acquired U-Pb age and trace element data (Mn, Sr, La, Ce, Sm, Eu, Gd, Lu); here again the data agree with literature constraints (when available) within uncertainties. The mapping approach is therefore a practical solution to low-temperature thermochronology studies facing apatite grains with low spontaneous fission-track densities, while also facilitating investigation of the spatial relationships between thermo- and geochronometric ages and grain chemistry.

中文翻译：

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通过 LA-Q-ICP-MS 成像进行磷灰石裂变径迹测年

摘要 获得准确和精确的磷灰石裂变径迹 (AFT) 年龄取决于样品中高质量磷灰石颗粒的可用性，理想情况下具有高自发裂变径迹密度 (c. >1.105 径迹.cm-2)。然而，许多天然样品，例如来自年轻造山带的基岩样品或低 U 含量的低变质样品，产生低自发裂变径迹密度。必须对此类磷灰石进行计数，以避免对所得 FT 年龄产生偏差。采用 LA-Q-ICP-MS 点烧蚀的 AFT 测年对于具有高自发裂变径迹密度的晶粒非常有效。这种方法允许检测潜在的 U 分区，同时还消除了对辐照步骤的需要，并促进了 U-Pb 和痕量元素数据的同时采集。因此，与外部检测器方法 (EDM) 相比，LA-Q-ICP-MS 点烧蚀具有多项优势。然而，光斑烧蚀方法需要计数区域精确模拟激光光斑的位置和大小，这对于具有低自发裂变径迹密度 (1.106 track.cm−2) 的晶粒来评估我们方法的精度和准确性。此处研究的大多数磷灰石样品之前都通过 EDM 或 LA-Q-ICP-MS 烧蚀点法确定了日期。AFT 晶粒映射年龄与先前公布的 EDM 或 LA-Q-ICP-MS 点烧蚀年龄在 2σ 水平上一致。对于每个磷灰石样品，我们同时获取了 U-Pb 年龄和微量元素数据（Mn、Sr、La、Ce、Sm、Eu、Gd、Lu）；这里的数据再次与不确定性内的文献限制（如果可用）一致。