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Poster communications

Cerium isotope systematics of oceanic carbonatites

Abstract : Oceanic carbonatites have been reported only at the Cape Verde and Canary archipelagos, North Atlantic Ocean. Geochemical studies based on stable, radiogenic and noble gas isotopes have led to the general consensus that their parental magmas originate in the mantle. Two contrasted models, however, have been proposed for the origin of the carbon of their source: recycled marine carbonates via subduction [Hoernle et al.. (2002) Cont. Mineral. Petrol. 142, 520-542; Doucelance et al.. (2010) GCA 74, 7261-7282] vs. primordial carbon [Mata et al.. (2010) EPSL 291, 70-83]. Marine carbonates [Plank & Langmuir (1998) Chem. Geol. 145, 325-394] show REE patterns distinct from those assumed or measured for mantle and mantle-derived reservoirs (D’’: [Tolstikhin et al.. (2006) Chem. Geol. 226, 79-99]; Lower Mantle: [Doucelance et al.. (2003) GCA 67, 3717- 3733]; DMM: [Workman & Hart (2005) EPSL 231, 53-72]; MORB: [Hofmann (1988) EPSL 90, 297-314]). Notably chondrite-normalized La/Ce and Sm/Nd ratios have inverse values. Consequently old recycled carbonates are likely to display εCe>0 (εCe is the 138Ce/142Ce variation relative to the Bulk Earth x10000) and εNd<0 (143Nd/144Nd variation relative to the Bulk Earth x10000) with time, whereas mantle-related materials will show εCe≤0 and εNd≥0. Thus coupled Ce and Nd isotope systematics appear to be a powerful tool to decipher between the two proposed origins for the carbon of oceanic carbonatites. We have measured Ce and Nd data on carbonatites from the Cape Verde and Canaries archipelagos, together with basaltic samples from the same locations. We have also determined εCe and εNd values for Tamazert carbonatites (Marocco) as it has been proposed that the Cape Verde, Canary and Tamazert carbonatites share a common source [Bouabdellah et al.. (2010) J. Petrol. 51, 1655-168]. Our first measurements on oceanic samples argue in favor of recycled marine carbonates in the source of oceanic carbonatites.
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https://hal.archives-ouvertes.fr/hal-02570326
Contributor : Régis Doucelance <>
Submitted on : Tuesday, May 19, 2020 - 10:53:50 AM
Last modification on : Tuesday, May 19, 2020 - 11:00:45 AM

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  • HAL Id : hal-02570326, version 1

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Régis Doucelance, Nina Bellot, Maud Boyet, Tahar Hammouda. Cerium isotope systematics of oceanic carbonatites. Goldschmidt Conference, Aug 2013, Florence, Italy. ⟨hal-02570326⟩

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