New Constraints on the Origin of the EM‐1 Component Revealed by the Measurement of the La‐Ce Isotope Systematics in Gough Island Lavas

• Published in: Geochemistry, Geophysics, Geosystems
• Main Authors: Boyet, M., Doucelance, R., Israel, C., Bonnand, P., Auclair, Delphine, Suchorski, K., Bosq, Chantal
• Other Authors: Laboratoire Magmas et Volcans (LMV), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS), ANR-10-LABX-0006,CLERVOLC,Clermont-Ferrand centre for research on volcanism(2010), ANR-16-IDEX-0001,CAP 20-25,CAP 20-25(2016)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; Gough; South Atlantic Ocean
• Online Access: https://uca.hal.science/hal-02156044; https://uca.hal.science/hal-02156044/document; https://uca.hal.science/hal-02156044/file/Boyet%20etal%20G3%202019.pdf; https://doi.org/10.1029/2019GC008228

International audience Hot spot lavas show a large diversity of isotope compositions resulting from the recycling ofsurface material into the convective mantle. Amongst the mantle end‐members, EM‐1 (enriched mantle)is widely debated and scenarios involving either old pelagic sediments subducted into the deep mantle orsubcontinental lithospheric material incorporated at shallow depths are commonly evoked. We selected 12lavas from Gough Island (south Atlantic Ocean) for the measurement of 138La‐138Ce, 147Sm‐143Nd, and176Lu‐177Hf isotope systems. Results show limited ranges for ε143Nd, ε138Ce, and ε176Hf values, and Ce/Ce*do not correlate with measured isotope ratios. Cerium isotope compositions allow us to exclude thecontribution of old sedimentary material carrying a negative, elemental cerium anomaly in the mantlesource. Pelagic sediments are indeed characterized by strongly negative, elemental cerium anomalies andalso high La/Ce ratios. Modeling a primitive mantle source contaminated by 0.4% to 2.2% of different 2.5Ga‐old pelagic components is able to reproduce the lowest Ce/Ce* values. However, the cerium isotopemeasurements show ε138Ce values between −0.39 and 0.15, too low to give support to the incorporation ofrecycled pelagic sediments in the mantle source of the lavas. Our results suggest that the incorporation ofsubcontinental lithospheric material at shallow depths during the plume ascent is a more suitable modelto explain the formation of the EM‐1 component. Hafnium and Nd isotopes also support this scenario.Subcontinental lithosphere sampled via kimberlites and lamproites has isotopic compositions that plotgenerally below the mantle array, a signature that is also seen in Gough lavas.