Geology and geochemistry of Neoarchaean subalkaline magmatism of the Keivy structure (Kola Peninsula).
Vetrin V. R.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2018. V. 147. N 3. P. 1-15
Subalkaline rocks of the Neoarchaean association of latites-monzonites-granites (ALMG), preserved as xenoliths and outliers among plagiomicrocline granites of the Keivy structure, were studied. This association of rocks have the lowered value of the Al/(Na+K) ratio, the high ferruginosity, elevated concentrations of highly charged and rare-earth elements, and correspond to granites of the A2-type. In contrast to the most common A-type granites, crystallized under reduced conditions and belonging to the ilmenite series, metavolcanites and hypabyssal granitoids of the ALMG contain an elevated amount of magnetite, which determines their attribution to rocks of the oxidized A-type. Formation of the ALMG magmas took place in the course of a fractional crystallization of initial melts with formation of restites consisting mainly of pyroxene, amphibole, magnetite, ilmenite, titanite and apatite.
Key words: Neoarchaean subalkaline rocks, petro- and geochemistry, petrology, Kola Peninsula.