Abstract
The existence of iron carbide in the upper mantle allows an assumption to be made about its possible involvement in the abyssal abiogenic synthesis of hydrocarbons as a carbon donor. Interacting with hydrogen donors of the mantle, iron carbide can form hydrocarbon fluid. In order to investigate the role of iron carbide in the abiogenic synthesis of hydrocarbons, the chemical reaction between cementite Fe3C and water was modeled under thermobaric conditions, corresponding to the upper mantle. A series of experiments were conducted using a high-pressure high-temperature Toroid-type large reactive volume unit with further analysis by means of gas chromatography. The results demonstrated the formation of hydrocarbon fluid in a wide range of thermobaric conditions (873–1223 K, 2.5–6.0 GPa) corresponding to the upper mantle. A strong correlation between the composition of the fluid and the pT conditions of the synthesis was illustrated in the investigation. The higher temperature of the synthesis resulted in the formation of a “poor” hydrocarbon mixture, primarily comprising methane, while a higher pressure yielded the opposite effect, converting iron carbide into a complex hydrocarbon system, containing normal and iso-alkanes up to C7 and benzene. This correlation explains the diversity of hydrocarbon systems produced experimentally, thus expanding the thermobaric range of the possible existence of complex hydrocarbon systems in the upper mantle. The results support the suggestion that the carbide—water reaction can be a source of both the carbon and hydrogen required for the abyssal abiogenic synthesis of hydrocarbons.
Highlights
A number of recent publications illustrate the abiogenic synthesis of complex hydrocarbon systems from inorganic substances under the thermobaric conditions of the upper mantle [1,2,3]
In order to investigate the role of iron carbide in the abiogenic synthesis of hydrocarbons, the chemical reaction between cementite Fe3C and water was modeled under thermobaric conditions, corresponding to the upper mantle
The results demonstrated the formation of hydrocarbon fluid in a wide range of thermobaric conditions (873–1223 K, 2.5–6.0 GPa) corresponding to the upper mantle
Summary
A number of recent publications illustrate the abiogenic synthesis of complex hydrocarbon systems from inorganic substances under the thermobaric conditions of the upper mantle [1,2,3]. The diversity of hydrocarbon systems experimentally synthesized in the lab from inorganic compounds is caused by the different thermobaric parameters of the synthesis, and by various initial donors of carbon and hydrogen in these reactions [3,4,5]. Iron carbides were never considered carbon donors for abiogenic hydrocarbon synthesis at high pressure until recent investigations [6,7]. The authors formulated a hypothesis that iron carbides could behave as donors of carbon in the abyssal abiogenic formation of hydrocarbons, interacting with hydrogen donors of the upper mantle [8,9]
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