Metasomatized Xenoliths of Mantle Eclogites and Garnet Pyroxenites from the V. Grib Kimberlite, Arkhangelsk Province

Abstract

We investigated mantle eclogite and garnet pyroxenite xenoliths from the V. Grib kimberlite located in the Arkhangelsk diamond province. The eclogites in the lithospheric mantle beneath the Arkhangelsk province were strongly modified by metasomatic processes, which totally obliterated the primary features of protolith. Detailed studies of the xenoliths allowed us to distinguish the following metasomatic events: (1) early mantle metasomatism and (2) interaction with kimberlite melt. During the multiple early mantle metasomatism, primary clinopyroxene and garnet were replaced by metasomatic clinopyroxene, garnet, amphibole, calcite, and phlogopite under the influence of carbonated ultramafic melts. The impact of kimberlite melt caused the dissolution and recrystallisation of solid-phase inclusions and formation of melt pockets consisting of serpentine, chlorite, carbonate, spinel, perovskite, amphibole, recrystallized garnet, and clinopyroxene. En route to the surface in kimberlite melt, the xenoliths were disintegrated and primary garnet and clinopyroxene were metasomatized with increasing Ti and Cr contents, up to formation of high-Cr megacrysts. The garnet pyroxenites are represented by high-Ca, low-Mg and low-Ca, high-Mg types. It is shown that the high-Ca, low-Mg garnet pyroxenites can be the final products of the eclogite xenolith metasomatism by carbonated ultramafic melts. The low-Ca, high-Mg pyroxenites were derived through the interaction of a partial eclogite melt with depleted peridotites.