Abstract
The Cambrian Kharly alkaline plutonic complex composed mainly of foidolite and nepheline syenite makes up a small intrusive field in the Sangilen Plateau in Tuva (southern Siberia). The rocks show large ranges of major oxides (38–58 wt% SiO2; 1–18 wt% Na2O + K2O; 11–28 wt% Al2O3; 1.5–20 wt% CaO; 0.1–8 wt% MgO; 2–12 wt% Fe2O3) controlled by variable percentages of minerals: clinopyroxenes, calcic amphiboles, micas, nepheline and feldspars. Alkaline rocks are cut by carbonatite veins composed of predominant calcite coexisting with femic minerals (10–15% of aegirine-ferrosalite-hedenbergite, sodic-calcic amphiboles, ferrobiotite, Ti-garnet), Na–K feldspar and nepheline (up to 15–20%), fluorapatite (up to 20–25%), Sr-apatite, and accessory carbocernaite, titanite, Ti-magnetite and ilmenite. Carbonatites (4057–8859 ppm Sr, 426–1901 ppm Ba (Sr/Ba ≥ 2), 290–980 ppm REE + Y, 2 to 100 ppm Zr, and 0.5 to 15 ppm Nb) possibly originated at high (≥500–650 °C) temperatures as a result of liquid immiscibility. The isotope systematics of rocks and minerals (εNd(t) from ~2.9 to 6.5; 207Pb/206Pbin = 0.89; 208Pb/206Pbin = 2.15; 87Sr/86Sr(t) = 0.70567–0.70733, δ18OV-SMOW ≈ 7.2–19.5‰, and δ13CV-PDB from −6.0 to −1.4‰) suggest mixing of PREMA and EM 1 material during magma generation and crustal contamination of the evolving melts. The rocks bear signatures of interaction with “magmatic-equilibrated” fluids or heated meteoric waters. LILE/HFSE ratios indicate mixed magma sources that involved the material of IAB and OIB, as well as a crustal component, possibly, due to interaction of a mantle plume with rock complexes on the active continental margin.
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