Comparative Characteristics of Middle Paleozoic and Late Riphean Plume Magmatism of the Siberian Platform

摘要

Based on isotopic and geochemical data for Late Riphean dikes and sills and for Devonian dolerite dikes and basalt covers within the Sette-Daban rift in the western part of the Siberian platform, we proved conceptions about the participation of various deep sources in their formation. The inverse correlation in Devonian basites between concentrations of Nb, light rare earth elements, and a number of other highly incompatible elements on the one hand and Zr, Y, and other moderate incompatible elements, including heavy rare earth elements on the other hand allows us to assume that two sources participated in the formation of melts. The source of dolerites is close to the EMORB type, and the source of basalts is close to the OIB type. The compositions of Riphean rocks correspond to a trend for which magma formation occurred with the participation of a source with characteristics between NMORB and EMORB and also a component typical of subduction zones. The data obtained imply associate formation of basites with the influence of mantle plumes on the lithosphere of the southeastern part of the Siberian craton in the Late Riphean and Middle Paleozoic. In the Riphean the plume mantle was composed of a moderately depleted mantle of the EMODB type and a mantle with the composition close to the above-subduction mantle, which was metosomatically changed under the influence of fluid water, which caused the appearance of a Nb and Ta deficit in melting products. The isotopic characteristics Nd (~(147)Sm/~(144)Nd = 0.165 and ε_(Nd)(T) ～ 2.3-4.7) of rocks show the moderate depleted nature of these sources.