Abstract
The ..delta..C/sup 13/ values in carbonatites of different composition and origin from the Maymecha-Kotuy province of Polar Siberia, the East Sayan province of Eastern Siberia, and the Karelia-Kola province, vary within very narrow limits: from -0.46% for the high-temperature calcitic generations up to -0.24% for the low-temperature dolomitic and ankerite-dolomitic generations of carbonatites. From an analysis of the ..delta..C/sup 13/ values obtained and their comparison with values for deep-seated carbon dioxide (average -0.7%) and carbon dioxide of marine carbonates (average approx. 0.0%), on the one hand, and also allowing for the thermodynamic isotope effect in the system CO/sub 2/ == CO/sub 3//sup -2/, on the other, it follows that the source of the carbon dioxide for the carbonatites may have been a mixture of deep-seated and sedimentary-carbonate CO/sub 2/. Judging by the ..delta..C/sup 13/ values for the high-temperature calcitic carbonatites (0.45/-0.46%), deep-seated carbon dioxide predominated in the original mixture. (JMT)
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