Abstract
A dike–vein complex of potassic type of alkalinity recently discovered in the Baikal ledge, western Baikal area, southern Siberian craton, includes calcite and dolomite–ankerite carbonatites, silicate-bearing carbonatite, phlogopite metapicrite, and phoscorite. The most reliable 40Ar–39Ar dating of the rocks on magnesioriebeckite from alkaline metasomatite at contact with carbonatite yields a statistically significant plateau age of 1017.4 ± 3.2 Ma. The carbonatite is characterized by elevated SiO2 concentrations and is rich in K2O (K2O/Na2O ratio is 21 on average for the calcite carbonatite and 2.5 for the dolomite–ankerite carbonatite), TiO2, P2O5 (up to 9 wt %), REE (up to 3300 ppm), Nb (up to 400 ppm), Zr (up to 800 ppm), Fe, Cr, V, Ni, and Co at relatively low Sr concentrations. Both the metapicrite and the carbonatite are hundreds of times or even more enriched in Ta, Nb, K, and LREE relative to the mantle and are tens of times richer in Rb, Ba, Zr, Hf, and Ti. The high (Gd/Yb)CN ratios of the metapicrite (4.5–11) and carbonatite (4.5–17) testify that their source contained residual garnet, and the high K2O/Na2O ratios of the metapicrite (9–15) and carbonatite suggest that the source also contained phlogopite. The Nd isotopic ratios of the carbonatite suggest that the mantle source of the carbonatite was mildly depleted and similar to an average OIB source. The carbonatites of various mineral composition are believed to be formed via the crystallization differentiation of ferrocarbonatite melt, which segregated from ultramafic alkaline melt.
Highlights
The Baikal ledge rock formations in the Siberian craton structure are included in the Akitkan mobile belt which is considered as the Late Paleoproterozoic independent island arc system moved up to the ancient basement during the terrains amalgamation 1.91–2.00 Ga ago (Fig. 1) [Rosen, 2003; Gladkochub et al, 2009; Didenko et al, 2013]
The rocks of the terraine basement are covered by terrigenous and volcanogenic-sedimentary formations of the Akitkan Group (PR1) and intruded by granitoids dated at 1.85–1.88 Ga [Neymark et al, 1998; Larin et al, 2003; Donskaya et al, 2008]
The Ilikta formation of the Sarma Group PR1 represented by metaeffusives of basic and intermediate composition, phyllites and sericite+chlorite-quartz schists containing carbonaceous material (CM), limestones, sandstones, tuff sandstones is developed within the Baikal ledge of southern flank (Fig. 1, b)
Summary
The Baikal ledge rock formations in the Siberian craton structure are included in the Akitkan mobile belt which is considered as the Late Paleoproterozoic independent island arc system moved up to the ancient basement during the terrains amalgamation 1.91–2.00 Ga ago (Fig. 1) [Rosen, 2003; Gladkochub et al, 2009; Didenko et al, 2013]. For citation: Danilova Yu.V., Savelyeva V.B., Shumilova T.G., Ivanov A.V., Danilov B.S., Bazarova E.P., 2017. New data on age and nature of carbonization within southern flank of the Baikal ledge of the Siberian craton basement.
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