The first data on variations of the isotope composition and element ratios of carbon, nitrogen, and argon in carbonatites of different generations and ultrabasic rocks of the Guli massif obtained by the method of step crushing are reported. It is shown that early carbonatite differs significantly from the later ones by the concentration of highly volatile components, as well as by the isotope compositions of carbon (CO2), argon, and hydrogen (H2O). The data obtained allow us to conclude that the mantle component predominated in the fluid at the early stages of formation of rocks of the Guli massif, whereas the late stages of carbonatite formation were characterized by an additional fluid source, which introduced atmospheric argon, and most likely a high portion of carbon dioxide with isotopically heavy carbon.

A great number of investigations has been devoted to study of fluid inclusions in mantle rocks and minerals. Most of them aimed to investigate the petrologic characteristics, such as P-T conditions of the inclusions formation and their chemical composition. The isotopic characteristics of the gases from the inclusions are studied in much less degree. However it is the isotopic research that could provide detailed information about fluid sources and fluid-rock interaction processes, the important factors of formation and alteration of geological objects. In continuation of the work on the investigation of isotopic characteristics of the mantle rocks fluid phase using stepwise crushing initiated by us [Buikin et al., 2009], we studied carbon, argon and nitrogen isotope variations and their elemental ratios in fluid inclusions from chilled basalt glasses, sampled during 31 cruise of the scientific research ship “Professor Logachev” in the MAR rift valley at 20–2230’ North, representing typical N-MORB (K2O/TiO2 = 0.08–0.10). The sample preparation technique including gas extraction and separation can be found in [Buikin et al., 2010]. Isotope compositions of carbon and oxygen from CO2 were analyzed on Thermo Finnigan Delta Plus mass-spectrometer (GEOKHI RAS) using «microvolume» system with cold finger, which allows to make reliable measurements of small gas amounts (0.01–0.02 cc). Argon and nitrogen isotope compositions were analyzed on a high-sensitivity complex Finesse consisting of three mass-spectrometers at the Open University (Milton Keynes, UK). Concentrations of helium and carbon (in the form of CO2) in the studied samples have been obtained on the same machine. It should be noted that the analyses of He, C, N and Ar have been performed simultaneously from the same sample. The obtained data are shown in figures 1–9 and table 1.

To get insight into the fluid regime evolution during formation of Guli massif (Maymecha-Kotuy magmatic complex, Syberia) carbonatites we have studied C, N and Ar isotopic and elemental ratios in foure carbonatite samples by stepwise crushing method. Mineral separates representing different formation stages of the massif have been selected for the investigation: two early calcites (Cal) and a late stage dolomite (Dol) and siderite (Sid). The early calcites are carachterized by significantly lower CO 2 content and lower δ 13 C values than the late Dol and Sid (-14.1, -13.6‰ and -9.0, -10.5‰ in average respectively). Fractionation during melt degassing (when system is closing) could lead to a higher CO 2 content with higher d 13 C values in the late minerals. But the results on C, N and Ar elemental compositions in the fluid inclusions have shown that C/N and C/Ar ratios also dramatically increase from the early to the late samples (C/N: from 7 in Cal to 210 in Sid and 2100 in Dol; C/Ar ; from 870 in Cal to 12300 in Sid and 159000 in Dol), which could not be caused by a simple magmatic fractionation. An additional source of CO 2 could appear at the late stages of the fluid-magmatic evolution of the massif. The data on C, N and Ar concentration variations in crushing steps support this assumption: well-defined correlations between concentrations of these elements in fluid inclusions are observed in the early Cal (i.e. all gases in the inclusions have the same elemental composition and concequently the same source). For the late Sid and Dol the situation is different: when N and Ar concentrations decrease with crushing steps, the C concentration is increasing, suggesting different sources for (N+Ar) and for most of CO 2 . Moreover, 40 Ar/ 36 Ar ratios in early and late samples are quite different: 3680 in Cal and 657 and 549 in Sid and Dol, respectively. This suggests the air-like argon component to be domineted in fluids during formation of the late minerals. Thus, relationships between C, N and Ar concentrations as well as differences in C and Ar isotopic compositions in fluid inclusions of the early and late carbonitites suggest that at the late stages of Guli massif carbonatites formation an additional CO 2 source with havier carbon and atmosphere-like Ar have contributed to the system.

(1991). SULFUR IN VOLCANIC ROCKS OF THE KAMCHATKA-KURILEJAPAN ISLAND ARC. International Geology Review: Vol. 33, No. 2, pp. 135-141.