Volume 32, Nº 6 (2024)

Large granitoid provinces can be divided into areal and linear types, which differ significantly in the area and volume of granitoids in their composition. It is shown using the example of the largest granitoid provinces of Central and Northeast Asia (Angara-Vitim, Khangai, Kalba-Narym, Kolyma). It is assumed that these differences are due to the structure of pregranitic basement and degree of thermal impact on the lower and middle continental crust. An important factor in the formation of granitoid provinces is mantle mafic magmatism, the estimated scale of which correlates with the volumetric and areal characteristics of the granitoid provinces. The role of mafic magmatism is an additional input of heat from the fluids into the melting region of crustal protoliths, as well as a material contribution that is realized through various mechanisms of magma mixing. Mixing at the deep level is the most effective, resulting in the formation of significant volumes of increased basicity salic magmas. The petrogenetic role of contrasting magmas mixing at the mesoabyssal level of the earth's crust, as well as in hypabyssal conditions (mingling dikes), is not great, but these manifestations are the key argument in justifying the synchronicity of mafic and granitoid magmatism. Granitoids of Silicic Large Igneous Provinces (SLIPs) are characterized by a heterogeneous isotopic composition, generally corresponding to the parameters of the continental crust. The extremely high heterogeneity of spatially conjugate granitoids due to the mixing of silicic magmas formed through the melting of a small number of sources with contrasting isotopic compositions, including through mixing with magmas of mantle origin. Mafic rocks included in the granitoid provinces correspond to the isotopic composition of the enriched mantle (Angara-Vitim batholith) or indicate a significant contribution of contamination with continental crust material (Khangai area). The metallogeny of SLIPs is determined by the erosional section size and the crustal protoliths type, the metamorphism degree of which largely determines the initial fluid content of silicic magmas. The melting of highly metamorphosed ancient crustal protoliths produces relatively “dry” silicic melts, the melting of low-metamorphosed crustal sources leads to the formation of “aqueous” melts, the differentiation of which ends with pegmatite formation with rare metal mineralization. Non-subduction origin SLIPs formation is associated with the mantle plumes impact (in the form of synchronous basaltoid magmatism) on the heated crust of young orogenic regions, where tectonic processes ended no more than a few tens of Ma.

New data are presented on the contents of major elements and trace elements, Sr-Nd-Pb isotopes in the Holocene high-potassium basic lavas of the Alaid volcano, located in the north of the Kuril island arc in the junction zone with the Kamchatka volcanic segment. According to petrochemical criteria, two groups of coeval rocks are distinguished: Ne-normative shoshonites and high-potassium subalkaline basalts, which are similar to each other in a number of geochemical characteristics. Chondrite-normalized REE distribution spectra show enrichment in LREE, with flat HREE distribution spectra, and the absence of Eu and Ce anomalies. MORB-normalized incoherent element concentrations show LILE enrichment and a well-defined negative Ta-Nb-Ti anomaly typical of suprasubduction volcanics. High K₂O/Rb and Rb/Sr ratios indicate the presence of biotite and amphibole in the magmatic source, while low Sr/Y ratios and flat distribution spectra of medium and heavy lanthanides indicate the absence of garnet in the restite paragenesis. Significant variations in the contents of macro- and microcomponents at similar MgO concentrations indicate a heterogeneous magmatic source, and taking into account linear mixing trends in isotope and discrimination diagrams, experimental data, suggest the involvement in magmogenesis of not only the peridotite mantle, but also amphibole-clinopyroxene mineral paragenesis. An analysis of the literature data shows that in «cold» island arcs, manifestations of potassium alkaline magmatism are often, if not in all cases, associated with local extension zones. Since such zones are associated with the adiabatic rise of a hot and plastic asthenosphere, it can be assumed that subduction melange formed along the boundary of the slab and supra-subduction mantle, consisting of hydrated fragments of ultrabasites and metamorphosed oceanic crust transformed into amphibole-bearing pyroxenites, was involved in the melting. This mechanism makes it possible to logically explain the geochemical and isotopic features of the anomalous alkaline magmatism of the Kuril island arc and the connection with the anomalous tectonics of its northern segment. The results obtained may be important in discussing the genesis of potassium alkaline magmas manifested in subduction geodynamic settings.