TY - JOUR

T1 - Origin of alkali-rich volcanic and alkali-poor intrusive carbonatites from a common parental magma

AU - Chayka, Ivan F.

AU - Kamenetsky, Vadim S.

AU - Vladykin, Nikolay V.

AU - Kontonikas-Charos, Alkiviadis

AU - Prokopyev, Ilya R.

AU - Stepanov, Sergey Yu

AU - Krasheninnikov, Stepan P.

N1 - Funding Information: The preparation of this paper has been overshadowed by Dr. N.V. Vladykin’s death on the 4th of July 2021. We had worked jointly on the samples he collected and discussed the ideas he expressed. We have done our best to complete the study. In sorrow, we dedicate this work to his memory. The authors thank Ivan Kuz’min for the help with the data processing, Maya Kamenetsky, Michael Zelensky and Alina Koshlyakova for assistance with experiments and sample preparation, Karsten Goemann, Mikhael Khlestov, Dmitry Varlamov, Viktoria Danilovskaya and Konstantin Van for assistance with SEM and EPMA. The paper has been improved from informal discussions with Anastasiya Iskrina and Andrey Izokh. We also thank Dr Robert F. Martin and the second anonymous reviewer, whose objections and recommendations were very helpful in improvement of the paper, as well as the handling editor Dr. Caterina De Vito. The study was performed by the State Assignment to IEM RAS (project AAAA-A18-118020590141-4). SEM and EPMA analyses in IGM SB RAS were financially supported by the grant of Russian Science Foundation #19-77-10004. Experiments and samples preparation were partially funded by the governmental assignment in terms of Project 0284-2021-0008. Publisher Copyright: © 2021, The Author(s).

PY - 2021/12

Y1 - 2021/12

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85114631075&partnerID=8YFLogxK

U2 - 10.1038/s41598-021-97014-y

DO - 10.1038/s41598-021-97014-y

M3 - Article

C2 - 34475480

AN - SCOPUS:85114631075

VL - 11

JO - Scientific Reports

JF - Scientific Reports

SN - 2045-2322

IS - 1

M1 - 17627

ER -