Geothermal systems developed in volcanic regions release magmatic volatiles that may forecast volcanic eruptions. These volatiles can be emitted directly in gaseous form to the atmosphere or can be absorbed by condensed geothermal fluid and groundwater that discharges at surface thermal features. The subsurface flow dynamics of these fluids are therefore crucial for the interpretation of their chemical and isotopic compositions. Furthermore, since geothermal fluids are globally used as energy and cultural resources, such information is also important for their sustainable management. In this context, we investigated the subsurface residence times of fluids from three geothermal areas in Shimabara peninsula (Unzen, Shimabara and Obama) by measuring their tritium and ³⁶Cl activities, along with their chemical and stable isotopic compositions. At Shimabara, the trace tritium activities of the geothermal fluids indicate that magmatic volatiles were transported by pre-nuclear (residence time >60 years) groundwaters. Tritium and δD-δ¹⁸O data indicate that the steam feeding the Unzen geothermal field is also derived from pre-nuclear meteoric water, and contributing about a quarter of the water budget. The ³⁶Cl/Cl ratio of the geothermal fluids in Obama exceeds that of seawater, indicating subsurface addition of nucleogenic chloride during prolonged water-rock interaction.

火山地区开发的地热系统释放出岩浆挥发物，可以预测火山喷发。这些挥发物可以以气态形式直接排放到大气中，也可以被冷凝的地热流体和在地表热特征排放的地下水吸收。因此，这些流体的地下流动动力学对于解释它们的化学和同位素组成至关重要。此外，由于地热流体在全球被用作能源和文化资源，因此此类信息对其可持续管理也很重要。在此背景下，我们通过测量来自岛原半岛的三个地热区（云仙、岛原和小滨）的氚和³⁶Cl 活性，以及​​它们的化学和稳定同位素组成。在岛原，地热流体的微量氚活动表明岩浆挥发物是由核前（停留时间 >60 年）地下水输送的。氚和δ D- δ ¹⁸ O 数据表明，供给云仙地热田的蒸汽也来自核前大气水，约占水收支的四分之一。奥巴马的地热流体的³⁶ Cl/Cl 比值超过了海水，表明在长时间的水岩相互作用过程中，地下添加了成核氯化物。