Geochemistry of mantle metasomatism related to formation of kimberlites in the northern East European Platform

Abstract

The geochemistry of mantle metasomatism related to the formation of kimberlites and allied rocks in the northern East European Platform (EEP) is considered with allowance for chemical systematics and geodynamic position. The Paleoproterozoic kimberlites of Kimozero, Mesoproterozoic orangeites of Karelia, Neoproterozoic kimberlites of Finland, and Devonian kimberlites of the Arkhangel’sk diamond province (ADP) are the objects of this research. Kimberlites from the EEP are characterized by wide variations in contents of rock-forming oxides and trace elements caused by secondary alteration, belonging to different lithofacies and specific sources. The diversity of kimberlites from the EEP is explained by the interaction of asthenospheric protokimberlitic melt with depleted or metasomatically enriched lithospheric mantle. A (Zr/Sm)n-Cr/Ni diagram has been proposed to identify specific attributes of mantle metasomatism. Comparison of the geodynamic setting of kimberlite formation in the EEP with the revealed geochemical features of mantle metasomatism shows that kimberlites having sources with the participation of MARID-type meta-somatic assemblages were formed under conditions of changing supercontinental cycles, when the breakdown of large supercontinent coincided in time with the initial stage of assembly of a new supercontinent. This is characteristic of the Kimozero kimberlites, orangeites of Karelia, and kimberlites from the ADP. Kimberlites of Finland were formed under geodynamic conditions characterized by supercontinent breakdown coeval with abundant within-plate mafic magmatism. These kimberlites bear geochemical features inherent to an asthenospheric source. The economic Devonian diamond-bearing kimberlites from the ADP display a subordinate role of the metasomatic lithospheric as a component of their source against the background of a significant interaction of melted asthenospheric material with the depleted lithospheric mantle.