Abstract
Discrete grains of subcalcic garnets from Yakutian kimberlites have been in- vestigated for major elements, Sm, Sr, Nd, Rb concentrations as well as for 875r/865r and l43Nd/l44Nd ratios. tp6;-values range between +1 and -40.6, 875r/865r are between 0.70521 and 0.72632, confirming the very heterogeneous character of these minerals. Sm/Nd ratios range from 0.025 to 0.828. Strong positive correlations of eSr/86Sr-ratios with Cr and Mn are consistent with an origin of the subcalcic garnets from Cr-spinels from spinel-harzburgites which were subducted into depths of the diamond stability field and reacted there with a metasomatic agent producing subcalcic garnet and oli- vine at the expense of Cr-spinel, orthopyroxene and any remaining clinopyroxene. It is proposed that subcalcic garnets are formed episodically through time and that kimber- lites randomly sample populations of these minerals which are not necessarily coge- netrc.
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