Isotopic patterns of hydrothermal hydrocarbons emitted from Mediterranean volcanoes
Isotopic patterns of hydrothermal hydrocarbons emitted from Mediterranean volcanoes
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DOI：
10.1016/j.chemgeo.2014.12.030
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发表时间：
2015-03
期刊：
影响因子：
3.9
通讯作者：
J. Fiebig;S. Hofmann;F. Tassi;W. D’Alessandro;O. Vaselli;A. Woodland
中科院分区：
文献类型：
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作者：
J. Fiebig;S. Hofmann;F. Tassi;W. D’Alessandro;O. Vaselli;A. Woodland
我们已经分析了CO2，甲烷，乙烷，丙烷和正丁烷的碳同位素组成，甲烷的氢同位素组成以及总浓度的气体成分中所含的地中海火山热液排放的尼西罗斯（希腊），维苏威火山，拉索尔法塔拉，伊斯基亚和潘泰莱里亚（所有意大利），以确定烃类的起源。同位素标准通常用于烃类分类建议热成因的起源，除了Pantelleria，其中一个非生物成因的起源表示。这些发现将意味着，产热源可以提供甲烷/（乙烷+丙烷）的浓度比通常观察到的微生物烃一样高。然而，对气体浓度数据的额外考虑挑战了对热液环境中产生的碳氢化合物进行分类的常规标准的适用性。甲烷似乎是在密切的平衡与共存的二氧化碳，而其更高的链同系物不是。因此，不能排除甲烷与乙烷、丙烷和正丁烷具有不同的来源。甲烷的碳同位素组成可能受到共存无机CO2的碳同位素组成和热液温度的控制，而高级正构烷烃的碳同位素组成可能对应于有机质的成熟度和/或气体的停留时间在源系统中。
We have analyzed the carbon isotopic composition of CO2, methane, ethane, propane and n-butane, the hydrogen isotopic composition of methane as well as total concentrations of gas constituents contained in the Mediterranean volcanic–hydrothermal discharges of Nisyros (Greece), Vesuvio, La Solfatara, Ischia and Pantelleria (all Italy) to determine the origin of the hydrocarbons. Isotopic criteria conventionally used for hydrocarbon classification suggest thermogenic origins, except for Pantelleria, for which an abiogenic origin is indicated. These findings would imply that thermogenic sources can provide methane/(ethane + propane) concentration ratios as high as those usually observed for microbial hydrocarbons. However, additional consideration of gas concentration data challenges the suitability of conventional criteria for the classification of hydrocarbons emanating from hydrothermal environments. Methane seems to be in close equilibrium with co-occurring CO2, whereas its higher chain homologues are not. Therefore, it cannot be excluded that methane on the one hand and ethane, propane and n-butane on the other hand have distinct origins. The carbon isotopic composition of methane might be controlled by the carbon isotopic composition of co-occurring inorganic CO2and by hydrothermal temperatures whereas the carbon isotopic composition of the higher n-alkanes could correspond to the maturity of organic matter and/or to the residence time of the gasses in the source system.