A comparative study of the petrology, mineralogy and geochemistry of kimberlite-like and carbonatitic rocks from Kontozero (Kola Peninsula, Russia) and bona fide kimberlites

The Kontozero diatreme (Kola Peninsula) comprises a suite of ultramafic alkaline and carbonatitic rocks including: kimberlite-like rocks, silicocarbonatites, phoscorites and intrusive and extrusive carbonatites. The kimberlite-like rocks have many petrologic similarities to bona fide kimberlites (North America), and the petrology, mineralogy and geochemistry of these rocks are compared. The major minerals present in the kimberlite-like rocks and kimberlites are very similar, and both have LREE-enriched, HREE-depleted trace-element signatures normalized to chondrite. The kimberlites are potassic [(K2O/Na 2O)average = 42.4] whereas the kimberlite-like rocks from Kontozero are sodic [(K2O/Na2O)average = 0.7]. Trace-elements plotted on a primitive mantle-normalized multi-element graph highlight significant differences between the two types of rocks. Average ratios of La/Yb, Sr/La and Zr/Nb are 28.0, 30.4 and 4.2 for the kimberlite-like rocks, respectively, and 301.7, 4.5 and 0.5 for the kimberlites, respectively. The kimberlite-like rocks and kimberlites must have originated from significantly different source regions in the mantle. (Abstract shortened by UMI.)...