Abstract
The article contains the results of statistical processing of a large summary of δ18О-δ13С isotope values in the primary carbonatites of the world. From literary sources, 1593 paired values δ18О-δ13С 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 δ18О (‰, V-SMOW) - δ13С (‰, V-PDV). For each carbonatite occurrence, not only the arithmetic mean values are calculated, but also the regression line. Distinct linear trend of δ18О-δ13С 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 δ18О-δ13С). 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 δ18О-δ13С values, probably due to the combined action of multidirectional trends. The initial ratio 87Sr/86Sr in the used carbonatite occurrences varies from 0.701 to 0.708. Statistics show no correlation of 87Sr/86Sr with the δ18О-δ13С system.
Highlights
Half of the carbonatite occurrences do not show a linear trend of δ18О-δ13С values, probably due to the combined action of multidirectional trends
Primary carbonatites demonstrate a wide variation of the δ18О-δ13С values and linear trends, which indicates the isotopic heterogeneity of carbonatite substance
The trend with an average angular coefficient of 0.30 sharply dominates. This is explained by the Rayleigh high-temperature fractionation of carbonatite melts or by their sedimentary contamination
Summary
The fields of primary igneous carbonatites on the δ18О-δ13С diagram are outlined in the works [1] [5] [6] [7]. These fields are used in the analysis of local isotope data in carbonatite studies. Authors of literature classify the analyzed material as primary carbonatites (PC). This is mainly done on the basis of petrographic studies, in which secondary endo- and exogenous minerals are not detected. The names of carbonatite occurrences and their identification number (ID) are coordinated with the database [8] and are given in English transcription
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