Petrogenesis of granitoids from silicic large igneous provinces (Central and North-East Asia)

Abstract

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.