THE METASOMATIC OLIVINE IN KIMBERLITES OF DYUKEN FIELD (ANABAR REGION)

摘要

In a kimberlites pipe of Dyukensky field in Prianabarye (Yakutian Province) there has been detected the meta-somatic olivine formed in the post-magmatic stage. It replaces phenocrysts of olivine related to its 1st and 2nd generations and occurs as separate grains in the rock matrix. Data on composition of olivines of different generations and other minerals of the kimberlite matrix are given in the paper. On the contrary to high ferruginousity of the 1 st and 2 nd olivines (15-19 and 11-14 percent of the Fa-component, respectively), the metasomatic olivine is the highly magnesium (with 2 to 7.8 percent Fa-compomnent). Peculiarities of its composition includes the elevated contents of MnO and CaO (0.38 and 0.5 percent_(wt)) and practical absence of NiO. Picroilmenite and phlogopite in the kimberlite matrix are high magnesium also (15.8--22 and 23.6--25.3 percent_(wt) MgO, respectively). Almost all minerals of the matrix have zonal structure. Great amount of oxides (picroilmenite, Cr-spinel, titanomagnetite, perovskite), wide variations of mineral compositions, zonal replacements, resorption, exsolution textures indicate the quite complicated nonequilibrium conditions of the rock matrix formation. The metasomatic olivine is supposed to be formed either as the deserpentinization of the partly serpentinized kimberlites, due to their addional heating, or resulted an interaction between consolidated kimberlite and the deep generated high-temperature fluid, containing K_2O and volatile components (F, CO_2).