THE “CLINOPYROXENE” PALEOGEOTHERM BENEATH THE OBNAZHENNAYA KIMBERLITE PIPE AND THIСKNESS OF LITHOSPHERE UNDER THE KUOYKA FIELD (SIBERIAN CRATON, YAKUTIA)

The mantle paleogeotherm under the Obnazhennaya kimberlite pipe (Kuoika field, Siberian craton) was reconstructed using the chemical composition of clinopyroxene xenocrystals and the FITPLOT program. The lithosphere thickness 187–193 km and surface heat flow 41–42 mW/m2 were measured for the Obnazhennaya pipe at the time of kimberlite magmatism in the Mesozoic. The lithosphere thickness was found to be much smaller than that in the central part of the Siberian craton (210–230 km), where Paleozoic diamond-bearing kimberlite pipes-deposits are located. It is however comparable to the highly diamond-bearing Kimberley field in the Kaapvaal craton (South Africa). The absence of diamonds in the pipes of the Kuoika field, but poor diamondiferous Dyanga pipe, might be associated with the more intense metasomatic alteration of the rocks within the lithospheric mantle of this region in the Mesozoic time, as compared to the central part of the Siberian craton in the Middle Paleozoic time.