Bulk carbon and clumped isotope composition of n-alkanes in volcanic-hydrothermal emissions
Final Report Abstract
It has been postulated that ethane, propane and n-butane can be generated abiogenically in crustal environments through polymerization of methane. We have analyzed the carbon isotopic composition of n-alkanes and the clumped isotopic composition of methane contained in hydrothermal gaseous emissions from Mediterranean volcanoes to obtain further constraints on the origin of the corresponding hydrocarbons. For all locations, carbon isotope distribution patterns amongst the n-alkanes are not in agreement with those proposed to be characteristic for the C2+ n-alkanes deriving from the polymerization of methane. For most of the studied locations the observed patterns are rather in agreement with the C2+ n-alkanes deriving from the thermogenic decay of organic matter. Methane may either be of a thermogenic origin, too, or originate from abiogenic reduction of inorganically derived CO2. Preliminary clumped isotope data on Nisyros methane yields an apparent internal equilibration temperature of 444 ± 80°C that is - within errors - still in agreement with the apparent carbon isotopic CO2-CH4 equilibration temperature of 358 ± 10°C received for the same sample. Independent proof of the attainment of heterogeneous isotopic equilibrium between CO2 and CH4 could point to an abiogenic origin of Nisyros methane.
Publications
- (2013) Biogeochemical processes involving dissolved CO2 and CH4 at Albano, Averno, and Monticchio meromictic volcanic lakes (Central-Southern Italy). Bull. Volc. 75:683
Cabassi, J., Tassi, F., Vaselli, O., Fiebig, J., Nocentini, M., Capecchiacci, F., Rouwet, D., and Bicocchi, G.
(See online at https://doi.org/10.1007/s00445-012-0683-0) - (2013) Carbon-bearing gas geothermometers for volcanic-hydrothermal systems. Chem. Geol. 351, 66-75
Fiebig, J., Tassi, F., D’Alessandro, W., Vaselli, O., and Woodland, A.B.
(See online at https://doi.org/10.1016/j.chemgeo.2013.05.006) - (2015) Isotopic patterns of hydrothermal hydrocarbons emitted from Mediterranean volcanoes. Chem. Geol. 396, 152-163
Fiebig, J., Hofmann, S., Tassi, F., D'Alessandro, W., Vaselli, O., and Woodland, A.B.
(See online at https://doi.org/10.1016/j.chemgeo.2014.12.030)
