Constraints on source-forming processes of West Greenland kimberlites inferred from Hf-Nd isotope systematics.

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Gaffney, Amy M., Blichert-Toft, Janne, Nelson, Bruce K., Bizzarro, Martin, Rosing, Minik, Albarède, Francis
• Other Authors: Department of Earth and Space Sciences Seattle, University of Washington Seattle, Laboratoire de Sciences de la Terre (LST), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Geological Museum Copenhagen, Natural History Museum of Denmark, Faculty of Science Copenhagen, University of Copenhagen = Københavns Universitet (UCPH)-University of Copenhagen = Københavns Universitet (UCPH)-Faculty of Science Copenhagen, University of Copenhagen = Københavns Universitet (UCPH)-University of Copenhagen = Københavns Universitet (UCPH), Nordic Centre of Earth Evolution (NORDCEE), University of Copenhagen = Københavns Universitet (UCPH)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2007
• Subjects: [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Greenland; Ocean Island
• Online Access: https://hal.science/hal-00337857; https://hal.science/hal-00337857/document; https://hal.science/hal-00337857/file/1-s2.0-S0016703707001172-main.pdf; https://doi.org/10.1016/j.gca.2007.03.009

International audience Kimberlites from West Greenland have Hf-Nd isotope as well as major and trace element compositions that are similar to other Group I kimberlites, but that are distinctive in the spectrum of magmas sampled at Earth's surface. The West Greenland kimberlites have εNdi that ranges from +1.6 to +3.1 and εHfi that ranges from −4.3 to +4.9. The samples exhibit ubiquitous negative ΔεHfi (deviation from the ocean island basalt εHf-εNd reference line), ranging from −1.8 to −11.2. The kimberlites are characterized by steep heavy rare earth element patterns, positive Ta-Nb anomalies and negative Hf-Zr anomalies. These chemical signals are consistent with the presence of ancient, subducted oceanic crust in the kimberlite source region. In the model we present, dewatering and possibly partial melting of rutile-bearing oceanic crust during subduction results in characteristic trace element patterns in the residual crust. During aging, the Hf-Nd isotopic composition of this dewatered/partially melted EMORB-type crust evolves to negative ΔεHfi values. Metasomatic fluids derived from this ancient subducted oceanic crust infiltrate and impart their trace element and isotopic signal on proximal peridotitic mantle. Melting of this metasomatized mantle peridotite results in kimberlite magmas.