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Russian Geology and Geophysics

2018 year, number 11


I.F. Chaika1,2, A.E. Izokh1,2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Лампроиты, расплавные включения, хромиты, Инаглинский массив, Алданский щит, Lamproites, melt inclusions, chromites, Inagli massif, Aldan Shield


We consider a hypothesis of the origin of PGE-bearing ultramafic rocks of the Inagli massif (Central Aldan) through fractional crystallization from ultrabasic high-potassium magma. We studied dunites and wherlites of the Inagli massif and olivine lamproites of the Ryabinovy massif, which is also included into the Central Aldan high-potassium magmatic area. The research is focused on the chemistry of Cr-spinels and the phase composition of Cr-spinel-hosted crystallized melt inclusions and their daughter phases. Mainly two methods were used: SEM-EDS (Tescan Mira-3), to establish different phases and their relationships, and EPMA, to obtain precise chemical data on small (2-100 μm) phases. The obtained results show similarity in chromite composition and its evolutionary trends for the Inagli massif ultramafites and Ryabinovy massif lamproites. The same has been established for phlogopite and diopside from crystallized melt inclusions from the rocks of both objects. Based on the results of the study, the conclusion is drawn that the ultramafic core of the Inagli massif resulted from fractional crystallization of high-potassium melt corresponding in composition to low-titanium lamproite. This conclusion is consistent with the previous hypotheses suggesting an ultrabasic high-potassium composition of primary melt for the Inagli ultramafites.