Dear Vratislav,


I would propose to read the fundamental papers of Yong-Fei Zheng (see
below). I also observed such trends in basalt- and lamprophyre-related
carbonates (although formed at much higher temperatures). Possible
explanations could be found in fractionations during CO2-H2O degassing
and associated changes in the carbonate-fluid isotope fractionation due
to XCO2 decrease.

Best regards,
Attila

Zheng, Y.-F. (1990): Carbon-oxygen isotopic covariation in hydrothermal
calcite during degassing of CO2. Mineral. Deposita, 25, 246-250.
Zheng, Y.-F., Hoefs, J. (1993): Carbon and oxygen isotopic covariations
in hydrothermal calcites. Mineralium Deposita, 28, 79-89.
Demeny, A., Forizs, I., Molnar, F. (1994): Stable isotope and chemical
compositions of carbonate ocelli and veins in Mesozoic lamprophyres of
Hungary. European Journal of Mineralogy, 6, 679-690.
Demeny, A., Harangi, Sz. (1996): Stable isotope studies on carbonate
formations in alkaline basalt and lamprophyre series: evolution of
magmatic fluids and magma-sediment interactions. Lithos, 37, 335-349.


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Dr. Attila Demeny
Geokemiai Kutatolaboratorium - Laboratory for Geochemical Research
Magyar Tudomanyos Akademia - Hungarian Academy for Sciences
Budapest, Budaorsi ut 45, H-1112, Hungary
Tel: (361-)309-2600/ ext. 1223 (office), 1394 (lab)
Tel/fax: (361-)319-3137
e-mail: [log in to unmask]
Http://www.core.hu/~demeny
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