The Sources and Evolution of Fluid Phases of Guli Massif Carbonatites (West Siberia): Summarizing of Noble Gases, N2, CO2, H2O Stepwise Crushing Data

AbstractHere we present summarizing of isotopic compositions and element ratios of noble gases, nitrogen, carbon and hydrogen in carbonatites of different generations of the Guli massif (West Siberia, Russia) obtained by stepwise crushing. The data point to the subcontinental lithospheric mantle (SCLM) as a primary source of the fluid phase in Guli carbonatites. However, the estimated 40Ar/36Ar ratio in the Guli mantle source of about 5400 is similar to the Kola plume value of 5000 ± 1000 (Marty et al., 1998). One explanation of such a low estimated 40Ar/36Ar ratio in the mantle end-member with SCLM type helium (4Не/3Не ~ 120000) and neon (21Nе/22Nеmantle ~ 0.7) is an admixture of atmospheric argon to the local mantle source. This assumption is supported by the Ar-Ne systematics as well as by the data for hydrogen isotopic composition. Early carbonatite differs significantly from the later ones by the concentration of highly volatile components, as well as by the isotopic compositions of carbon (CO2), argon, and hydrogen (H2O). The mantle component dominated in fluids at the early formation stages of the Guli massif rocks, whereas the late stages of carbonatite formation were characterized by an additional fluid source, which introduced atmospheric argon and neon, and most likely a high portion of CO2 with isotopically heavy carbon. The argon-neon-hydrogen isotope systematics suggest that the most plausible source of these late stage fluids are high temperature paleometeoric waters. The absence of a plume signature could be explained in terms that Guli carbonatites have been formed at the waning stage of plume magmatic activity with an essential input of SCLM components.