Identifying the processes that govern the hydrogen isotopic composition of H2 and CH4 in fumarolic emissions: a case study from Nisyros, Greece

以往对地热井排放的研究表明，H2、CH4和H2O之间的氢同位素分配可以反映含水层深层温度。然而，对于天然气中H2、CH4和H2O在地壳上升过程中的同位素平衡行为几乎一无所知。通过分析希腊Nisyros火山-热液排放物中H2、CH4和H2O的体同位素组成和CH4的团块同位素组成，确定控制H2-H2O和CH4-H2O氢同位素分馏的过程，并确定热液中CH4和H2的体同位素组成和团块同位素组成在从储层上升到喷口表面的过程中被重置的程度。需要这些资料，以便能够利用氢和成团的同位素数据来评估甲烷的来源，并通过监测地表排放的气体的化学和同位素组成的变化来确定火山活动的状况。

Previous investigations on discharges from geothermal wells revealed that hydrogen isotope partitioning between H2, CH4 and H2O can reflect aquifer reservoir temperature at depth. However, almost nothing is known about the isotopic equilibration behavior between H2, CH4 and H2O in natural gases ascending through the crust. We seek to analyze the bulk isotopic composition of H2, CH4 and H2O and the clumped isotopic composition of CH4 in volcanic-hydrothermal emissions from Nisyros volcano, Greece, to identify the processes exerting control on the apparent H2-H2O and CH4-H2O hydrogen isotope fractionations and to determine to what extent the bulk and clumped isotopic compositions of hydrothermal CH4 and H2 are reset during their ascent from the reservoir to the venting surface. Such information is required to be able to assess the origin of methane by means of hydrogen and clumped isotope data and to determine the state of volcanic activity by monitoring variations in the chemical and isotopic composition of the gases discharging at the surface.