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Russian Geology and Geophysics

2005 year, number 5


V.V. Ryabov and D.E. Grib
Institute of Geology, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Multiphase dikes, petrography, mineralogy, Siberian craton
Pages: 462-476


We studied multiphase symmetrical dikes that cross-cut Triassic tuff lavas in the Kamen' alkali mafic province in the northern Siberian craton, especially, the structure of vitreous and crystalline dikes, their petrography, major-element compositions, and mineralogy. The dike swarm has a symmetrical structure produced by compositionally similar left-hand and right-hand half-dikes. The dikes show five phases of melt injection. Vitreous dikes are composed of olivine-clinopyroxene or occasionally picritic (in the center) porphyry. Each half-dike consists of a quench contact with spherulites of silicic glass and carbonate and an inner zone with feldspar, and feldspar with kaersutite and/or mica. Early phases in crystalline dikes are variolitic clinopyroxenites and late phases are picritic porphyry. The rock chemistry and mineralogy indicate presumably limburgite composition of the parent melt. The multiphase dikes originated by repeated melt injection into pulse-like opening fractures whereby the melt moving along the magma conduit underwent differentiation with separation of magnesian fluid. Overcooling of the limburgite melt in the dikes provided separation of carbonatite and alkali-silicic fluids and heteromorphic crystallization of variolitic clinopyroxenites.