Metasomatic processes in the lithospheric mantle beneath the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province,Russia) |
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| Affiliation: | 1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;2. A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia;3. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;1. A.P. Vinogradov Institute of Geochemistry, 1a Favorsky st., Irkutsk, 664033, Russia;2. V.S.Sobolev Institute of Geology and Mineralogy, 3 Koptyuga ave., Novosibirsk, 630090, Russia;3. Novosibirsk State University, 2 Pirogova st., Novosibirsk, 630090, Russia;1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;2. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;1. Dept of Geology, Rhodes University, Grahamstown 6140, South Africa;2. School of Earth and Ocean Sciences, Cardiff University, Cardiff, Wales;3. Department of Earth Science, Rice University, Houston, TX 77005, USA;1. Institute of Geology and Mineralogy SD RAS, Koptyug ave 3, Russian Federation, 630090 Novosibirsk, Russia;2. Institute of Geochemistry SD RAS, Irkutsk, Russia;3. Vienna University, A-1090 Vienna, Austria;4. Alrosa Stock Company, Mirny, Russia;5. Birkbeck College, University of London, UK;6. Institute of Geology of Diamond and Noble Metals SD RAS, Yakutsk, Russia |
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| Abstract: | New data on metasomatic processes in the lithospheric mantle in the central part of the Arkhangelsk diamondiferous province (ADP) are presented. We studied the major- and trace-element compositions of minerals of 26 garnet peridotite xenoliths from the V. Grib kimberlite pipe; 17 xenoliths contained phlogopite. Detailed mineralogical, petrographic, and geochemical studies of peridotite minerals (garnet, clinopyroxene, and phlogopite) have revealed two types of modal metasomatic enrichment of the lithospheric-mantle rocks: high temperature (melt) and low-temperature (phlogopite). Both types of modal metasomatism significantly changed the chemical composition of the peridotites. Low-temperature modal metasomatism manifests itself as coarse tabular and shapeless phlogopite grains. Two textural varieties of phlogopite show significant differences in chemical composition, primarily in the contents of TiO2, Cr2O3, FeO, Ba, Rb, and Cs. The rock-forming minerals of phlogopite-bearing peridotites differ in chemical composition from phlogopite-free peridotites, mainly in higher FeO content. Most garnets and clinopyroxenes in peridotites are the products of high-temperature mantle metasomatism, as indicated by the high contents of incompatible elements and REE pattern in these minerals. Fractional-crystallization modeling gives an insight into the nature of melts (metasomatic agents). They are close in composition to picrites of the Izhmozero field, basalts of the Tur’ino field, and carbonatites of the Mela field of the ADP. The REE patterns of the peridotite minerals make it possible to determine the sequence of metasomatic enrichment of the lithospheric mantle beneath the V. Grib kimberlite pipe. |
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