"""Microscopic blebs of sulfur-bearing organic matter (OM) commonly occur between the secondary calcite grains and fibrous phyllosilicates in extensively serpentinized and carbonated mantle-derived ultramafic xenoliths from Hyblean nephelinite diatremes. Sicily, Italy. Rarely, coarse bituminous patches give the rock a blackish color. Micro Fourier transform infrared spectra (mu-FTIR) point to asphaltene-like structures in the OM, due to partially condensed aromatic rings with aliphatic tails consisting of a few C atoms. X-ray photoelectron spectroscopy (XPS) analysis indicates the occurrence of minor SO (either sulphonyl or sulphoxide) functional groups in the OM. Solubility tests in toluene, thermo-gravimetric (TGA) and differential thermal (DTA) analyses confirm the presence of asphaltene structures. It is proposed that asphaltenes derive from the in situ aromatization (with decrease in H\\\\\\\/C ratio) of previous light aliphatic hydrocarbons. Field evidence excludes that hydrocarbon from an external source percolated through the xenolith bearing tuff-breccia. The discriminating presence of hydrocarbon in a particular type of xenolith only and the lack of hydrocarbon in the host breccia matrix, are also inconsistent with an interaction between the ascending eruptive system and a supposed deep-seated oil reservoir. Assuming that the Hyblean unexposed basement consists of mantle ultramafics and mafic intrusive rocks having hosted an early abyssal-type hydrothermal system, one can put forward the hypothesis that the hydrocarbon production was related to hydrothermal activity in a serpentinite system. Although a bacteriogenesis or thermogenesis cannot be ruled out, the coexisting serpentine, Ni-Fe ores and hydrocarbon strongly suggest a Fischer-Tropsch-type (FIT) synthesis. Subsequent variations in the chemical and physical conditions of the system, for example an increase in the water\\\\\\\/rock ratio, gave rise to partial oxidation and late carbonation of the serpentinite hosted hydrocarbon. Admitting an authigenic origin for most of the modal calcite (30-50% by volume) in these rocks. one can conclude as a general rule that un-carbonated serpentinites tectonically emplaced at shallow crustal levels are potential reservoir rocks (as well putative source rocks) for exploitable petroleum reserves."""
Scirè, S., Ciliberto, E., Crisafulli, C., Scribano, V., Bellatreccia, F., DELLA VENTURA, G. (2011). Asphaltene-bearing mantle xenoliths from Hyblean diatremes, Sicily. LITHOS, 125, 956-968 [10.1016/j.lithos.2011.05.011].
Asphaltene-bearing mantle xenoliths from Hyblean diatremes, Sicily
BELLATRECCIA, FABIO;DELLA VENTURA, Giancarlo
2011-01-01
Abstract
"""Microscopic blebs of sulfur-bearing organic matter (OM) commonly occur between the secondary calcite grains and fibrous phyllosilicates in extensively serpentinized and carbonated mantle-derived ultramafic xenoliths from Hyblean nephelinite diatremes. Sicily, Italy. Rarely, coarse bituminous patches give the rock a blackish color. Micro Fourier transform infrared spectra (mu-FTIR) point to asphaltene-like structures in the OM, due to partially condensed aromatic rings with aliphatic tails consisting of a few C atoms. X-ray photoelectron spectroscopy (XPS) analysis indicates the occurrence of minor SO (either sulphonyl or sulphoxide) functional groups in the OM. Solubility tests in toluene, thermo-gravimetric (TGA) and differential thermal (DTA) analyses confirm the presence of asphaltene structures. It is proposed that asphaltenes derive from the in situ aromatization (with decrease in H\\\\\\\/C ratio) of previous light aliphatic hydrocarbons. Field evidence excludes that hydrocarbon from an external source percolated through the xenolith bearing tuff-breccia. The discriminating presence of hydrocarbon in a particular type of xenolith only and the lack of hydrocarbon in the host breccia matrix, are also inconsistent with an interaction between the ascending eruptive system and a supposed deep-seated oil reservoir. Assuming that the Hyblean unexposed basement consists of mantle ultramafics and mafic intrusive rocks having hosted an early abyssal-type hydrothermal system, one can put forward the hypothesis that the hydrocarbon production was related to hydrothermal activity in a serpentinite system. Although a bacteriogenesis or thermogenesis cannot be ruled out, the coexisting serpentine, Ni-Fe ores and hydrocarbon strongly suggest a Fischer-Tropsch-type (FIT) synthesis. Subsequent variations in the chemical and physical conditions of the system, for example an increase in the water\\\\\\\/rock ratio, gave rise to partial oxidation and late carbonation of the serpentinite hosted hydrocarbon. Admitting an authigenic origin for most of the modal calcite (30-50% by volume) in these rocks. one can conclude as a general rule that un-carbonated serpentinites tectonically emplaced at shallow crustal levels are potential reservoir rocks (as well putative source rocks) for exploitable petroleum reserves."""I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
