Isotope Composition of Gases of Magmatic and Sedimentary Volcanic Systems: A Review and Comparative Analysis

Abstract

This article presents the results of a comparative analysis of the isotopic–geochemical composition of gases from igneous/hydrothermal and sedimentary volcanic systems in various regions of the world based on a large amount of literature data and the results of the author’s own research. The purpose of the study is to evaluate the nature of gases of various volcanic systems using known genetic criteria developed as a result of many years of research by a number of scientists from around the world. Data processing for the purpose of comparative analysis and corresponding graphical constructions have been performed using standard computer programs. A comprehensive analysis of the isotopic composition of carbon-rich gases and the isotopic ratio of helium (R/Ra) allows us to draw the following main conclusions: (1) hydrocarbon (HC) gases of the studied volcanic systems have different genetic sources: (a) abiogenic in igneous and carbonic sedimentary volcanic systems, (b) predominantly abiogenic–biogenic in the hydrothermal system, and (c) biogenic (thermogenic–microbial) in sedimentary volcanoes; (2) the content of abiogenic methane in the magmatic/hydrothermal system is insignificant and does not exceed 1%; (3) the isotope composition of CO₂ and the ratio of isotopes of radiogenic and air argon (⁴⁰Ar/³⁶Ar) in igneous volcanoes varies within very narrow limits when compared with sedimentary volcanoes. However, the use of these parameters as an unambiguous genetic criterion is not possible.