Hydrocarbons in Icelandic volcanic-hydrothermal discharges: An inventory of concentrations and preliminary bulk carbon, radiocarbon and clumped isotopic data

已经提出了几个标准来指示自然系统中非生物成因碳氢化合物的产生。其中包括i)正构烷烃之间的碳同位素分布模式和ii)CH4和CO2之间的明显平衡。然而，有必要更详细地了解控制二氧化碳、甲烷和高链正构烷烃之间碳同位素分馏程度的参数，以便更严格地评估这些标准作为烃类成因指示的适用性。在几个地中海火山-热液系统中，甲烷似乎与二氧化碳处于平衡状态。所有这些被研究的系统都有一个共同点，即在深部伴生的热液储集层比海水更多地出现盐分，并且温度总是接近相应的咸水的临界点。我们要求提供资金，将我们的工作扩展到冰岛的火山热液排放。冰岛火山-热液系统的多样性为进一步探索火山环境中的油气形成过程提供了独特的机会。与地中海系统不同的是，冰岛的许多火山-热液储集层1)有稀薄的大气水，2)温度远远超过水的临界点，3)部分由来自下地幔的气体提供。冰岛和地中海排放的化学和同位素数据的比较将提高我们对盐度、温度和下地幔的贡献在多大程度上控制二氧化碳和甲烷之间的质量交换的认识。此外，我们打算获得高于甲烷的正构烷烃的初步碳同位素数据，关于甲烷的放射性碳和聚集同位素(13C-D)数据，以获得关于火山-热液系统中碳氢化合物来源的更多信息。这项研究的目的是改进现有的采样技术，以便能够对正构烷烃进行整体碳同位素分析，以及对冰岛排放物中所含甲烷进行放射性碳和块状同位素分析。

Several criteria have been proposed to be indicative for abiogenic hydrocarbon production in natural systems. Amongst these are i) carbon isotope distribution patterns between n-alkanes and ii) apparent attainment of equilibrium between CH4 and CO2. However, a more detailed knowledge about the parameters exerting control on the extent of C-isotope fractionation between CO2, CH4 and higher chain n-alkanes is necessary to more critically evaluate the suitability of these criteria as indicators of hydrocarbon origin. In several Mediterranean volcanic-hydrothermal systems, CH4 seems to be in equilibrium with CO2. All these investigated systems have in common that the associated hydrothermal reservoirs at depth occur more saline than seawater and that temperatures are always close to the critical point of the corresponding saline waters. We request funding to extend our work to volcanic-hydrothermal discharges on Iceland. The diversity of Icelandic volcanic-hydrothermal systems represents a unique opportunity to further explore hydrocarbon formation processes in volcanic environments. In contrast to the Mediterranean systems, many volcanic-hydrothermal reservoirs on Iceland i) host dilute meteoric waters, ii) exhibit temperatures well beyond the critical point of water and iii) are partially fed by gases deriving from the lower mantle. A comparison of chemical and isotopic data for Icelandic and Mediterranean discharges will improve our knowledge to what extent salinity, temperature and contributions from the lower mantle governs mass exchange between CO2 and CH4.Furthermore, we intend to acquire preliminary carbon isotope data on n-alkanes higher than methane, radiocarbon and clumped isotope (13C-D) data on methane to gain additional information on the origin of hydrocarbons in volcanic-hydrothermal systems. This study aims at improving existing sampling techniques so that bulk carbon isotope analysis on n-alkanes as well as radiocarbon and clumped isotope analysis on methane contained in Icelandic discharges becomes possible.