ISOTOPIC COMPOSITION OF STRONTIUM IN INDIAN KIMBERLITES

Strontium isotopic studies on twenty three whole rock kimberlites from two petrographic provinces in India show variation of initial 87Sr 86Sr ratios from 0.7027 to 0.7102. The variation is unrelated to the degree of alteration. Between the micaceous and basaltic varieties there is some overlap in the Sr isotopic ratios. Leaching experiments on whole rock samples showed more highly radiogenic Sr in leaches compared to the bulk samples. In two diatremes, the initial 87Sr 86Sr ratios show a positive correlation with Rb Sr which is believed to reflect a source event earlier than the formation of the kimberlites. The observed Sr isotopic data can be caused by (i) melting of a heterogeneous source or (ii) disequilibrium partial melting in the source region. In the former case, variable isotopic composition would be a necessary consequence of melting in small subsystems. © 1979.