Oxygen and Carbon Isotope Composition in Primary Carbonatites of the World: Data Summary and Linear Trends

摘要

The article contains the results of statistical processing of a large summary of δ ~(18)О- δ ~(13)С isotope values in the primary carbonatites of the world. From literary sources, 1593 paired values δ ~(18)О- δ ~(13)С from 173 carbonatite occurrences of the world were collected. This report exceeds all previously published reports on С-О isotopes in carbonatites by quantity of the used values and carbonatite occurrences. Statistical data analysis is performed on diagrams in the coordinates δ ~(18)О (‰, V-SMOW) - δ ~(13)С (‰, V-PDV). For each carbonatite occurrence, not only the arithmetic mean values are calculated, but also the regression line. Distinct linear trend of δ ~(18)О- δ ~(13)С values is found in half of the carbonatite occurrences. The starting, middle, and ending points of the trend line are determined. The slope of the trend line (angular coefficient) varies over a wide range. The trend is dominated by an average angular coefficient of 0.30 (positive correlation δ ~(18)О- δ ~(13)С). In the literature, it is associated with the Rayleigh high-temperature fractionation of carbonatite melts or with their sedimentary contamination. Half of the carbonatite occurrences do not show a linear trend of δ ~(18)О- δ ~(13)С values, probably due to the combined action of multidirectional trends. The initial ratio ~(87)Sr/~(86)Sr in the used carbonatite occurrences varies from 0.701 to 0.708. Statistics show no correlation of 87Sr/86Sr with the δ ~(18)О- δ ~(13)С system.