Sources of matter for Neoarchaean subalkaline magmatic rocks of the Keivy structure (Kola Peninsula)

The Neoarchaean subalkaline magmatism of Keivy structure is expressed in formation of the volcano-plutonic association of latite-monzonite-granite (ALMG). The quantity of the measured relation ¹⁴³Nd/¹⁴⁴Nd in rocks is determined in 0.511061-0.511365, and values of model age are located in an interval from 3.14 to 3.21 billion years at εNd (2670) from 2.2 to -1.3. The initial relations ¹⁷⁶Hf/¹⁷⁷Hf in zircon are in limits 0.280950-0.281069, and figurative points of composition form the field around a trend of the CHUR. According to the isotope and geochemical data for all rocks the basic composition of protholits is supposed. In quantity εHf(T) points of zircon are localized in the field of the development of the crust with ¹⁷⁶Lu/¹⁷⁷Hf = 0.015 and 3.0-3.3 billion years age. It probably demonstrates the formation of initial melts mainly at the expense of matrix with a long time of stay in crust. The formation of ALMG magmas is assumed to appear due to the melting of metasomatically altered rocks of the lower crust during intrusion of basaltic melts initial for the rocks of the dike complex and the gabbro-labradorite massifs into the upper crust.