Proterozoic Kivakka layered mafic-ultramafic intrusion, Northern Karelia, Russia: Implications for the origin of granophyres of the Upper boundary group

Abstract Granophyric rocks on Earth are enigmatic and may be investigated by detailed sampling, empirical method and modeling. This work presents recent results on the 2445 ± 5 Ma Kivakka layered mafic-ultramafic intrusion in Northern Karelia, Russia, in particular, leucocratic lenses in the upper cumulative zone. Based on detailed sampling, mineralogical and petrologic investigation coupled with COMAGMAT petrologic modeling, the following sequence of the fractional crystallization of the main rock-forming minerals is established: olivine, olivine + orthopyroxene, orthopyroxene, orthopyroxene + plagioclase, orthopyroxene + plagioclase + augite, plagioclase + augite + pigeonite. We propose a petrologic model of the leucocratic granophyric rock origin from the residual melt produced at late stages of evolution of the Kivakka massif via closed-system fractional crystallization and convective mixing of magma in the chamber. Comparison of the granophyric rocks with lunar KREEP and granophyric rocks of other terrestrial massifs is performed based on the major and trace element composition of the rocks and minerals. We believe that the Proterozoic granophyric rock origin on Earth may be comparable to the origin of the lunar KREEP rocks due to high differentiation degree of the parental basaltic magma.