Origin of alkali-rich volcanic and alkali-poor intrusive carbonatites from a common parental magma

Ivan F Chayka; Vadim S Kamenetsky; Nikolay V Vladykin; Alkiviadis Kontonikas-Charos; Ilya R Prokopyev; Sergey Yu Stepanov; Stepan P Krasheninnikov

doi:10.1038/s41598-021-97014-y

Origin of alkali-rich volcanic and alkali-poor intrusive carbonatites from a common parental magma

Sci Rep. 2021 Sep 2;11(1):17627. doi: 10.1038/s41598-021-97014-y.

Authors

Ivan F Chayka^{1

2}, Vadim S Kamenetsky^{3

4}, Nikolay V Vladykin⁵, Alkiviadis Kontonikas-Charos^{6

7}, Ilya R Prokopyev^{8

9}, Sergey Yu Stepanov¹⁰, Stepan P Krasheninnikov¹¹

Affiliations

¹ Institute of Experimental Mineralogy, Russian Academy of Sciences, Akademika Osipyana Str., 4, Chernogolovka, Russia, 142432. ivanlab211@gmail.com.
² V.S. Sobolev Institute of Geology and Mineralogy Siberian Branch of the Russian Academy of Sciences, Koptyuga prospekt., 3, Novosibirsk, Russia, 630090. ivanlab211@gmail.com.
³ Institute of Experimental Mineralogy, Russian Academy of Sciences, Akademika Osipyana Str., 4, Chernogolovka, Russia, 142432.
⁴ Institute of Volcanology and Seismology, Far Eastern Branch of the Russian Academy of Sciences, Petropavlovsk-Kamchatsky, Russia, 683000.
⁵ Vinogradov Institute of Geochemistry SB RAS, 1a Favorsky St., Irkutsk, Russia, 664033.
⁶ Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institute Freiberg for Resource Technology, Chemnitzer Str. 40, 09599, Freiberg, Germany.
⁷ School of Chemical Engineering and Advanced Materials, The University of Adelaide, Adelaide, SA, 5005, Australia.
⁸ V.S. Sobolev Institute of Geology and Mineralogy Siberian Branch of the Russian Academy of Sciences, Koptyuga prospekt., 3, Novosibirsk, Russia, 630090.
⁹ Department of Geology and Geophysics, Novosibirsk State University, Novosibirsk, Russia, 630190.
¹⁰ Federal State Budgetary Insitution "A.P.Karpinsky Russian Geological Research Institute" (FGBU "VSEGEI"), St. Petersburg, Russia, 199106.
¹¹ Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin St. 19, Moscow, Russia, 119991.

Abstract

The discrepancy between Na-rich compositions of modern carbonatitic lavas (Oldoinyo Lengai volcano) and alkali-poor ancient carbonatites remains a topical problem in petrology. Although both are supposedly considered to originate via fractional crystallization of a "common parent" alkali-bearing Ca-carbonatitic magma, there is a significant compositional gap between the Oldoinyo Lengai carbonatites and all other natural compositions reported (including melt inclusions in carbonatitic minerals). In an attempt to resolve this, we investigate the petrogenesis of Ca-carbonatites from two occurrences (Guli, Northern Siberia and Tagna, Southern Siberia), focusing on mineral textures and alkali-rich multiphase primary inclusions hosted within apatite and magnetite. Apatite-hosted inclusions are interpreted as trapped melts at an early magmatic stage, whereas inclusions in magnetite represent proxies for the intercumulus environment. Melts obtained by heating and quenching the inclusions, show a progressive increase in alkali concentrations transitioning from moderately alkaline Ca-carbonatites through to the "calcite CaCO₃ + melt = nyerereite (Na,K)₂Ca₂(CO₃)₃" peritectic, and finally towards Oldoinyo Lengai lava compositions. These results give novel empirical evidence supporting the view that Na-carbonatitic melts, similar to those of the Oldoinyo Lengai, may form via fractionation of a moderately alkaline Ca-carbonatitic melt, and therefore provide the "missing piece" in the puzzle of the Na-carbonatite's origin. In addition, we conclude that the compositions of the Guli and Tagna carbonatites had alkali-rich primary magmatic compositions, but were subsequently altered by replacement of alkaline assemblages by calcite and dolomite.

Abstract

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