The First Measurements of δ~(13)C in Methane from CO_2-Rich Springs near the Elbrus Volcano

摘要

As is known, the CO_2-rich springs of the northern Caucasus are associated with Pliocene-Quaternary volcanic activity and are localized near the Elbrus and Kazbek volcanoes, in the Caucasian Mineral'nye Vody (CMV) district, and elsewhere. We sampled 98 of such springs in 1998-2001 (Fig. 1). Gas phase released during the discharge of such waters commonly consists of carbon dioxide (90-99 vol %). Occasionally, the CO_2 content drops to 40-50%. Such a gas composition is typical of the springs that are distinguished by the least gas factor (sporadic gas release). In addition to carbon dioxide, the studied gases consist of nitrogen (locally, up to 97 vol %), methane (considerable amounts in some places), and admixtures of argon, helium, hydrogen, and oxygen. The CH_4, Ar, and He contents are mutually correlated, indicating the general dilution of a gas mixture with CO_2. The methane content in 98 studied samples varied from 7 x 10~(-5) to 19.93 vol % (0.96 vol %, on average).