COMPOSITION OF HYDROCARBONS IN HYDROTHERMAL CARBONACEOUS MATERIAL AND THEIR GEOCHEMICAL SIGNIFICANCE

Abstract

Using indirect data and correcting for the presence of primary polynuclear aromatic hydrocarbons (PNA's) in minerals associated with diamond (olivine and pyrope) and of liquid hydrocarbons in melt inclusions from xenocrysts of olivine from kimberlite, we give preference to a subcrustral origin of the carbon. But the problem of possible borrowing of carbon-containing substances from the surrounding rocks is still unsolved. In this paper we propose to solve the problem by using various natural and experimental data on the conditions of generation and composition of various hydrocarbon series. Our investigations indicate that the structural properties of the PNA's, and especially the presence of alkylated hydrocarbons with a predominance of alklynaphthanes, is consistent with the idea that they were generated by polycondensation under reducing conditions at low temperatures and is entirely in agreement with the geological conditions of their generation. The presence of cyclic hydrocarbons, i.e., triterpenoids and steranes, indicates that the hydrothermal system extracted the organic matter from country rock in the crust.