Silicon isotopes reveal recycled altered oceanic crust in the mantle sources of Ocean Island Basalts

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Pringle, Emily, Moynier, Frédéric, Savage, Paul, Jackson, Matthew, Moreira, Manuel, Day, James M.D.
• Other Authors: Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Department of Earth and Planetary Sciences St Louis, Washington University in Saint Louis (WUSTL), Institut Universitaire de France (IUF), Ministère de l'Education nationale, de l’Enseignement supérieur et de la Recherche (M.E.N.E.S.R.), University of St Andrews Scotland, Department of Earth Sciences Durham, Durham University, Department of Earth Science Santa Barbara (GEOL-UCSB), University of California Santa Barbara (UC Santa Barbara), University of California (UC)-University of California (UC), Scripps Institution of Oceanography (SIO - UC San Diego), University of California San Diego (UC San Diego), We thank the three anonymous reviewers as well as the Associ-ate Editor Fangzhen Teng for their thorough reviews and com-ments, which have greatly improved this paper. EP thanks theChateaubriand STEM fellowship program for funding. FM thanksthe European Research Council under the European Community’sH2020 framework program/ERC grant agreement #637503 (Pris-Fig. 5. Plot of OIBd30Si as a function of the fraction of recycled component present in the melt derived from the mantle source. The dashedline and shaded box represent the average Si isotopic composition (±2 se) of the light-isotope enriched OIB measured in this study (Iceland,Mangaia, Cape Verde). The BSE reservoir is considered to have an elemental Si concentration Si = 0.21 andd30Si =0.29 (Savage ,2014). The recycled component is modeled with a nearly identical bulk Si = 0.23 but variabled30Si values. Here0.50,0.75, and1.00 areused as illustratived30Si values for the bulk recycled component; these values are consistent with altered oceanic crust (An , 2016)oramixture of altered oceanic crust with a few percent of sediments (d30Si values between2‰and4‰; see text for details). The Si isotopecompositions of the anomalous OIB localities are consistent with the incorporation of 10–30% recycled material in the plume source melt.292E.A. Pringle / Geochimica et Cosmochimica Acta 189 (2016) 282–295tine) and the Agence Nationale de la Recherche for a chaired’Excellence Sorbonne Paris Cite ́(IDEX13C445) and for the Uni-vEarthS Labex program (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). PS thanks the support of the Marie Curie FP7-IOF fellowship ‘‘Isovolc”, ANR-11-IDEX-0005,USPC,Université Sorbonne Paris Cité(2011), European Project: 637503,H2020,ERC-2014-STG,PRISTINE(2015), European Project: 328772,EC:FP7:PEOPLE,FP7-PEOPLE-2012-IOF,ISOVOLC(2013)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: Silicon isotopes; Ocean Island Basalts; Mantle heterogeneity; Recycling; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; Indian; Pacific; Iceland; Ocean Island
• Online Access: https://insu.hal.science/insu-02917544; https://insu.hal.science/insu-02917544/document; https://insu.hal.science/insu-02917544/file/Savage_2016_GCA_Basalts_AAM.pdf; https://doi.org/10.1016/j.gca.2016.06.008

International audience The study of silicon (Si) isotopes in Ocean Island Basalts (OIB) has the potential to discern between different models for the origins of geochemical heterogeneities in the mantle. Relatively large (∼several per mil per atomic mass unit) Si isotope fractionation occurs in low-temperature environments during biochemical and geochemical precipitation of dissolved Si, where the precipitate is preferentially enriched in the lighter isotopes relative to the dissolved Si. In contrast, only a limited range (∼tenths of a per mil) of Si isotope fractionation has been observed from high-temperature igneous processes. Therefore, Si isotopes may be useful as tracers for the presence of crustal material within OIB mantle source regions that experienced relatively low-temperature surface processes in a manner similar to other stable isotope systems, such as oxygen. Characterizing the isotopic composition of the mantle is also of central importance to the use of the Si isotope system as a basis for comparisons with other planetary bodies (e.g., Moon, Mars, asteroids).Here we present the first comprehensive suite of high-precision Si isotope data obtained by MC-ICP-MS for a diverse suite of OIB. Samples originate from ocean islands in the Pacific, Atlantic, and Indian Ocean basins and include representative end-members for the EM-1, EM-2, and HIMU mantle components. On average, δ30Si values for OIB (−0.32 ± 0.09‰, 2 sd) are in general agreement with previous estimates for the δ30Si value of Bulk Silicate Earth (−0.29 ± 0.07‰, 2 sd; Savage et al., 2014). Nonetheless, some small systematic variations are present; specifically, most HIMU-type (Mangaia; Cape Verde; La Palma, Canary Islands) and Iceland OIB are enriched in the lighter isotopes of Si (δ30Si values lower than MORB), consistent with recycled altered oceanic crust and lithospheric mantle in their mantle sources.