DEEP CARBON CYCLE AND GEODYNAMICS: THE ROLE OF THE CORE AND CARBONATITE MELTS IN THE LOWER MANTLE
N.L. Dobretsova,b and A.F. Shatskiyb,c,d
aA.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bNovosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
cV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
dDivision of Earth and Planetary Material Sciences, Department of Earth Science, Tohoku University, Sendai, 980-8578 Japan
Keywords: Geodynamics, carbon circle, carbonatite melt, kimberlite diamond
Pages: 1117-1132
Abstract
Carbon, though being abundant in the Solar system, barely exceeds 0.01 wt.% in the silicate mantle, whereas it is ~3.6 wt.% in primitive chondritic meteorites that most likely formed our planet. This deficit may be due to redistribution of carbon in the liquid metal phase and then in the core at the stage of magma ocean fractionation, because carbon is much more soluble in Fe-Ni ± S melt than in silicate melts. The terrestrial heat and mass transfer are controlled mainly by layered convection and periodic peaks of plume activity as fast mantle jets that rise from the core. Plumes carry significant amounts of CO2, H2O, and K2O (most probably in the form of carbonatite or hydrous carbonatite melts) released by the degassing core on its interaction with oxidized silicate material. There are two mechanisms that may maintain fast plume ascent: (1) local melting at the plume front as a result of doping with volatiles (H2O, CO2) as in a gas burner (rise rate 60-110 cm/yr) or (2) flow controlled by diffusion transport of silicate components in carbonatite melt (rise rate ~100 cm/yr).
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