U-Pb Age of Sphene and the Petrochemical, Mineralogical, and Geochemical Features of Alkaline Rocks of the Bogdo Complex (Arctic Siberia)

摘要

In the northern part of the Siberian Platform, east of the Anabar Shield, several massifs of alkaline rocks with carbonatites identified (Tomtor, Bogdo, Promezhutochnyi) and projected according to geophysical data (Bualkalakh, Chuempe, Uele) form a large alkaline-carbonatite province. The first data on the composition of alkaline rocks of the Bogdo massif indicate that the latter belong to a group of feldspathoid rocks of basic composition: rischorrites, biotite-aegirine liebenerite syenites, carbonatized pseudo-leucite nepheline syenites with symplectites, and nepheline-feldspar aggregates. Sphene grains were extracted from various rocks of the Bogdo massif, and their U-Pb age was determined using the SHRIMP-II secondary-ion microprobe. The calculated U-Pb age is 394.4 +/- 3.2 Ma, which is similar to the age of the Tomtor massif and the age of the rocks of the Kola alkaline province. One of the reasons for the manifestation of alkaline plume magmatism on this territory may be the effect of the peripheral zone of the African Large Low Shear Velocity Province ("Tuzo") on the Baltic area and Siberia during the Devonian age.