Calcium isotopic evidence for the mantle sources of carbonatites

Elsa Amsellem (1) , Frédéric Moynier (1, 2) , Hervé Bertrand (3) , Amaury Bouyon (1) , João Mata (4) , Sebastian Tappe (5) , James M. D. Day (6)

1 IPGP (UMR_7154) - Institut de Physique du Globe de Paris
2 IUF - Institut universitaire de France
3 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement
4 Instituto Dom Luiz
5 UJ - University of Johannesburg [South Africa]
6 SIO - UC San Diego - Scripps Institution of Oceanography

The origin of carbonatites-igneous rocks with more than 50% of carbonate minerals-and whether they originate from a primary mantle source or from recycling of surface materials are still debated. Calcium isotopes have the potential to resolve the origin of carbonatites, since marine carbonates are enriched in the lighter isotopes of Ca compared to the mantle. Here, we report the Ca isotopic compositions for 74 carbonatites and associated silicate rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with 0 and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle-derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. This signature reflects the composition of the source, which is isotopically light and is consistent with recycling of surface carbonate materials into the mantle

Mots clés: OLDOINYO-LENGAI; SILICATE ROCKS; NOBLE-GAS; CA CYCLE; FRACTIONATION; SUBDUCTION; EVOLUTION; ORIGIN; SERPENTINITES; CLINOPYROXENE

Domaines: Géochimie

Elsa Amsellem, Frédéric Moynier, Hervé Bertrand, Amaury Bouyon, João Mata, et al.. Calcium isotopic evidence for the mantle sources of carbonatites. Science Advances , 2020, 6 (23), pp.eaba3269. ⟨10.1126/sciadv.aba3269⟩. ⟨insu-02916256⟩