Subducted sediments play a key role in the evolution of the continental crust and upper mantle. As part of the deep carbon cycle, hydrocarbons are accumulated in sediments of subduction zones and could eventually be transported with the slab below the crust, thus affecting processes in the deep Earth’s interior. However, the behavior of hydrocarbons during subduction is poorly understood. We experimentally investigated the chemical interaction of model hydrocarbon mixtures or natural oil with ferrous iron-bearing silicates and oxides (representing possible rock-forming materials) at pressure-temperature conditions of the Earth’s lower crust and upper mantle (up to 2000(±100) K and 10(±0.2) GPa), and characterized the run products using Raman and Mössbauer spectroscopies and X-ray diffraction. Our results demonstrate that complex hydrocarbons are stable on their own at thermobaric conditions corresponding to depths exceeding 50 km. We also found that chemical reactions between hydrocarbons and ferrous iron-bearing rocks during slab subduction lead to the formation of iron hydride and iron carbide. Iron hydride with relatively low melting temperature may form a liquid with negative buoyancy that could transport reduced iron and hydrogen to greater depths.

Raman spectroscopy studies on n and i-butane were performed at pressures of up to 40 GPa at ambient temperatures using the DAC technique. Normal butane undergoes two phase transitions at 1.9(5) GPa and 2.9(5) GPa and isobutane at 2.7(5) GPa and 3.5(5) GPa. These phase transitions were identified based on observations of the splitting Raman modes and the appearance or disappearance of particular Raman peaks. Our results demonstrate the complex, high-pressure behavior of butane isomers.

The concentration of carbon dioxide and methane in the atmosphere has significantly increased over the last 60 years. One of the factors in the growth of methane and its homologue emissions is the intense thawing of gas hydrates, mainly from the Arctic shelf, which remains one of the less studied sources of atmospheric hydrocarbon emissions. Oxidation of methane and light-saturated hydrocarbons by ozone in the upper part of the atmosphere leads to the formation of CO₂. The analysis of several datasets presented in this paper allows us to find the correlation between CH₄ and CO₂ concentrations in the atmosphere. This finding suggests that methane and its homologues released from gas hydrates mainly in the Arctic shelf zone become a significant source of carbon dioxide in the atmosphere. Because the amount of hydrocarbons located in gas hydrate deposits on the Arctic shelf is huge, further evolution of this process can become a serious challenge.

Emerging of mass-spectroscopy with inductively-coupled plasma (ICP-MS) made possible to study the microelement composition of crude oil and its derivatives (with the limit of detection at the ppt level). We have studied the crude oil composition of some West Siberian and Tatarstan oilfields with the ICP-MS method to detect 50 rare, rare-earth, and other microelements. The elemental composition is reasonably comparable to their concentrations in ultrabasites whereas the contents of most of the elements are low to the limit. On the diagrams of rare-earth elements, one can see the prevalence of light lanthanides and positive europium anomaly. The study shows that crude oils have a specific microelement composition that stands out from other geological systems.