Hydrocarbon formation in CaCO3–FeO–H2O–SiO2 and Fe3C–H2O–SiO2 systems under thermobaric conditions of the upper mantle

Research subject. The possible influence of the SiO2 environment as the most common component of the mantle on the deep abiogenic synthesis of hydrocarbons in the CaCO3–FeO–H2O and Fe3C–H2O systems under thermobaric conditions corresponding to those in the upper mantle is investigated.Materials and methods. Experiments were carried out using a high-pressure unit in Toroid-type chambers across the thermobaric range of 2.0–4.0 GPa and 220–750°C. CaCO3 and Fe3C were used as carbon donors, H2O was used as a hydrogen donor, and SiO2 was used as an environment. The synthesized products were analyzed by gas chromatography and X-ray diffraction.Results. Across the entire temperature and pressure range used, mixtures of light alkanes with the predominance of methane were obtained. The composition of the hydrocarbon systems synthesized in the presence of SiO2 was similar to that obtained at the same thermobaric parameters without SiO2, depending exclusively on the temperature and pressure of synthesis. The conducted X-ray diffraction analysis of solid products demonstrated transformation of quartz into coesite at 400°C and 750°C.Conclusions. According to the conducted investigation, the qualitative and quantitative composition of hydrocarbon systems formed during the abiogenic synthesis of hydrocarbons in the presence of SiO2 corresponds to the results of similar experiments without SiO2. However, the total yield of the hydrocarbon systems in the SiO2 environment decreases. The dependence of the composition of the synthesized hydrocarbon systems on the thermobaric conditions of synthesis remains in the SiO2 environment.