Early Paleozoic alkaline basic magmatism in the Kuznetsk Alatau is manifested in the Upper Petropavlovka pluton of gabbro, feldspathoid rocks (theralites, mafic foidolites, and nepheline syenites), and Ca-carbonatites. According to Sm–Nd and Rb–Sr isotope data, the pluton formed in the Middle Cambrian (509 ± 10 Ma). The silicate igneous rocks correspond in the contents of silica, alumina, and alkalies to derivates of a K–Na alkaline basic association. The Ca-carbonatites are characterized by a high-temperature (600–900 °C) paragenesis of apatite, clinopyroxene, ferromonticellite, phlogopite, and magnetite. They are enriched in P2O5 (up to 6.4 wt.%), Sr (up to 3000–4500 ppm; Sr/Ba ~ 5–7), and REE + Y (up to 800 ppm) and show evidence for liquation genesis. The predominant magmatic source (εNd(T) = 5–7) was moderately depleted PREMA, possibly combined with E-MORB and EM. According to the isotopic data ((87Sr/86Sr)T ~ 0.7024–0.7065; δ18O ~ 6.3–15.5‰; δ18C ~ –3.5 to –2.0‰), the fractionation of the melts was accompanied by their crustal contamination. The trace-element composition of the mafic rocks testifies to the participation of a substance similar to the substrata of the parental magmas of MORB, IAB, and OIB in the magma generation. This suggests intrusion in the geodynamic setting of interaction between the active continental margin and an ascending mantle diapir. Most likely, the intrusion led to the mixing of material from different sources, including the components of PREMA, enriched suprasubduction lithospheric mantle (EM), and continental crust. The assumption is made that the complexes of highly alkaline rocks and carbonatites in the western Central Asian Fold Belt are of plume origin and belong to an Early Paleozoic large igneous province.

We report the first data on ⁴⁰Ar/³⁹Ar dating, trace-element geochemistry, and isotope (Nd, Sr, O) composition of the Belaya Gora gabbro-foidolite-foyaite intrusive massif, one of typical representatives of the alkaline province of the northeastern Kuznetsk Alatau. The established age of rock-forming amphibole, ~ 401-403 Ma, is taken as the time of the pluton formation in the Early Devonian. The distribution and ratios of LILE and HFSE in the rocks suggest that the intrusion took place in the setting of “superposition” of Devonian mantle plume on the Early Paleozoic accretion-collision complexes. Therefore, the source of magmatic products had a heterogeneous composition as a result of mixing of plume material with the substances of suprasubduction and crustal substrates. The mantle component might have been a PREMA + EM combination, which is confirmed by the parameters of the Nd isotope composition (£_NdT - 3.2-4.6; T_Nd(DM) - 0.8 Ga) of alkaline rocks. 87 86 18 The effects of crustal contamination are reflected in the high ratios of strontium and oxygen isotopes ( Sr/ Sr)_T - 0.7046-0.7054; 5 O - 8.5-9.2%c, SMOW).

We present new data on the U-Pb age of zircons, geochemistry of trace elements, and isotope (Nd, Sr, O) composition of rocks of the Kogtakh gabbro-monzonite complex on the eastern slope of the Kuznetsk Alatau Ridge. The established age of zircon in the rocks of the main intrusive phases (500-480 Ma) is taken as the time of formation of the Kogtakh complex in the Late Cambrian-Early Ordovician, during the accretion-collision stage of evolution of the Central Asian Orogenic Belt. The distribution and ratios of LILE and HFSE in the rocks suggest that the intrusions proceeded under interaction of the PREMA + EM/OIB mantle plume and the suprasubductional lithospheric IAB mantle. The mantle-crust interaction led to the heterogeneous isotopic composition of neodymium in the magma source (ɛ_Nd(T) ~ 3.5-5.4). The mixing of different mantle and continental-crust materials resulted in an increase in isotope parameters: (⁸⁷Sr/⁸⁶Sr)_T ~ 0.7039-0.7052, ɛ_Sr(T) ~ 0-19, and δ¹⁸O ~ 6.5-8.8‰ (SMOW). The REE ratio in the least differentiated gabbroids indicates different depths of probable magma chambers and the formation of their primary (Tb/Yb_PM > 1.8) mafic melts at different degrees of melting of the model garnet peridotite.

A new Wenlockian zircon U–Pb age (~426 Ma) of the Overmaraat-Gol nepheline syenite (foyaite, juvite) pluton in the SW Lake Hovsgol area (Northern Mongolia) prompts a long history of alkaline magmatism in the western Central Asian Orogenic Belt, exceeding the duration of the Devonian and Permian–Triassic events. The LILE and HFSE patterns of pluton samples analyzed by X-ray fluorescence (XRF) and inductively coupled plasma (ICP-MS) methods indicate intrusion in a complex tectonic setting during interaction of a mantle plume with accretionary-collisional complexes that previously formed on the active continental margin. As a result, the parent magma had a heterogeneous source with mixed mantle (PREMA and EM) and crustal components. This source composition is consistent with Nd–Sr isotope ratios of the Overmaraat-Gol alkaline rocks, from −0.1 to −1.2 ε_Nd(t) and from ~0.706 to 0.707 ⁸⁷Sr/⁸⁶Sr(t).

The isotope geochemistry (εNd( t) 4.8–5.4, 206Pb/204Pb in 18.05–18.36, 207Pb/204Pbin 15.53–15.57, 208Pb/204Pb in 37.59–37.83, 87Sr/86Sr( t) 0.7048–0.7057, δ18OSMOW8–10.5‰) and trace element...

Cambrian, Devonian and Permian differentiated intrusions made up of subalkaline and alkaline gabbro, foidolite, nepheline and alkaline syenites, and rare carbonatites compose an area in the northern part of the Kuznetsk Alatau alkaline igneous province. Primary melts of the intrusions were moderately fractionated ((La/Yb)_N up to 7–12) and could be derived by 1–10% partial melting of mantle spinel lherzolite. The LILE and HFSE distribution in the mafic rocks (Rb 6–58, Ba 111–2499, Sr 175–1555, REE 28–208, Zr 40–315, Nb 1.5–52, Th 0.3–12, U 0.2–7.4, ppm) indicates the involvement of OIB- and IAB-type oceanic and marginal-continental lithosphere materials in magma generation. A source of the parental melt was heterogeneous and consisted of a mixture of depleted (PREMA and E-MORB) and enriched (EM-type) mantle magmas with an intermediate isotopic ratio ε_Nd(Т) ~ 3–9. Apparent heterogeneity of the source is reflected in the initial Pb isotopic composition of rocks and minerals: ²⁰⁸Pb/²⁰⁴Pb = 37.49–38.12, ²⁰⁷Pb/²⁰⁴Pb = 15.53–15.71, ²⁰⁶Pb/²⁰⁴Pb = 17.92–20.65. The subsequent upper crustal contamination of the melts led to a simultaneous increase in the isotopic ratios (⁸⁷Sr/⁸⁶Sr)_Т ~ 0.7042–0.7074; δ¹⁸О_V-SMOW ~ 6.3–15.5‰, as well as to the enrichment of rocks in ²⁰⁷Pb. Geochemical data suggest that primary melts were formed by impact of a mantle plume (OIB-type hot spot) on accretion-collisional complexes of the former active continental margin. Such geodynamic setting provides the generation of heterogeneous magma sources even within a small igneous province.