Low-temperature chronometers offer potential to gain insights into the temporal evolution of hydrothermal systems. The long-lived fault-bound Grimsel pass hydrothermal system (including a fossil and an active part) in the Central European Alps serves here as a key site to test such an application. Zircon and apatite grains were separated from samples collected along a fault transect. The resulting zircon (U-Th)/He ages are homogenous along the profile at 8–9 Ma and thus record the regional cooling evolution, remaining unaffected by the younger hydrothermal activity. In contrast, the apatite (U-Th)/He ages show three age groups: One Group (1) of ca. 5 Ma inside and outside the hydrothermal zone matches the low-temperature part of the regional cooling trend, while group (2) with ages as young as 1–2 Ma occurs in a central narrow zone associated with hydrothermal activity. One sample (group 3) displays older apparent ages compared to the regional cooling trend. Group (2) apatite samples reveal a different cathodoluminescence texture and trace-element chemistry, which we interpret together with the young age as apatite growth or re-crystallization within the hydrothermal system. Forward 1D modelling of He diffusion indicates that apatite (U-Th)/He ages should always be reset when exposed to hot thermal waters (up to ~140 °C) present over ka timescales or to intermediate temperature waters (~90 °C) over Ma timescales. Combining our measured apatite (U-Th)/He ages with forward modelling results highlight that, besides regional cooling trends, local heat anomalies within hydrothermal zones are very variable in space and time. Combined trace-element geochemistry and (U-Th)/He dating shows local occurrence of newly-formed apatites crystals, which are best described as geochronometers rather than thermochronometers. Such information is important to explore the longevity of hydrothermal systems and associated spatial distributions of heat anomalies.

低温天文钟提供了深入了解热液系统时间演变的潜力。中欧阿尔卑斯山长期存在的断层限制 Grimsel 通道热液系统（包括化石和活动部分）在这里作为测试此类应用的关键地点。锆石和磷灰石颗粒从沿断层断面收集的样品中分离出来。由此产生的锆石 (U-Th)/He 年龄在 8-9 Ma 沿剖面是同质的，因此记录了区域冷却演化，不受年轻热液活动的影响。相比之下，磷灰石 (U-Th)/He 年龄显示三个年龄组：一组 (1) 约。热液带内外5 Ma与区域降温趋势的低温部分相匹配，而年龄低至 1-2 Ma 的组 (2) 出现在与热液活动相关的中央狭窄区域。与区域降温趋势相比，一个样本（第 3 组）显示出更古老的表观年龄。第 (2) 组磷灰石样品显示出不同的阴极发光结构和微量元素化学，我们将其与年轻时代一起解释为水热系统内的磷灰石生长或重结晶。He 扩散的前向 1D 建模表明，当暴露于 ka 时间尺度上存在的热水（高达 ~140 °C）或中温水（~90 °C）时，应始终重置磷灰石 (U-Th)/He 年龄超过马时间尺度。将我们测量的磷灰石 (U-Th)/He 年龄与正向建模结果相结合，突出表明，除了区域冷却趋势外，热液带内的局部热异常在空间和时间上变化很大。结合微量元素地球化学和 (U-Th)/He 测年显示新形成的磷灰石晶体的局部出现，最好将其描述为地球计时仪而不是热计时仪。这些信息对于探索热液系统的寿命和热异常的相关空间分布很重要。