Combined Nd and Hf isotope evidence for deep-seated source of Isua lavas

• Published in: Earth and Planetary Science Letters
• Main Authors: Rizo, Hanika, Boyet, Maud, Blichert-Toft, Janne, Rosing, Minik
• Other Authors: Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet Saint-Étienne (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement Lyon (LGL-TPE), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon), Natural History Museum of Denmark, Faculty of Science Copenhagen, University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU), Nordic Centre of Earth Evolution (NORDCEE), University of Copenhagen = Københavns Universitet (KU), European Research Council under the European Community : 209035
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2011
• Subjects: Hf isotopes; Nd isotopes; Nd-142; Isua amphibolites perovskite; Hadean; geo; hist; Canada; Greenland; Northwest Territories
• Online Access: https://doi.org/10.1016/j.epsl.2011.10.014; https://hal-insu.archives-ouvertes.fr/insu-00673487

International audience We present the first combined Sm-146.147-Nd-142,Nd-143 and Lu-176-Hf-176 study of mafic rocks (amphibolites) from the western part of the Isua Supracrustal Belt (ISB, SW Greenland). Sm-Nd and Lu-Hf whole-rock isochrons yield identical ages within error: 3.72 +/- 0.08 and 3.67 +/- 0.07 Ga, respectively. Nd-142 measurements confirm and extend the database of Nd-142 excesses in Isua samples (mu Nd-142 = 7-16 ppm relative to the terrestrial Nd standard), indicating that early-differentiated reservoirs escaped complete homogenization by mantle convection until the Archean. Combined Sm-146,Sm-147-Nd-142,Nd-143 systematics suggest differentiation of the Isua amphibolite reservoir at maximum ages of similar to 4.53, similar to 4.47, and similar to 4.32 Ga. These ages are relative to, respectively, ordinary-chondritic, enstatite-chondritic, and higher-than-chondritic mantle compositions. The intercept of the Sm-Nd whole-rock isochron is in accordance with Nd-142 results and consistent with a superchondritic initial Nd-143/Nd-144 ratio (epsilon Nd-143(3.7Ga) = +1.41 +/- 0.98). In contrast, the corresponding initial epsilon Hf-176(3.7Ga) = -1.41 +/- 0.57 is subchondritic. Since Lu/Hf and Sm/Nd fractionate similarly during mantle processes, the Sm-Nd and Lu-Hf isotope systems display incongruent relative parent-daughter behavior in the source of Isua amphibolites. Based on high-pressure and -temperature phase partition coefficients, we propose a model that satisfies Sm-147-Nd-143, Lu-176-Hf-176, and Nd-142 results, as well as trace element characteristics. A deep-seated source composed largely of magnesium perovskite (98% MgPv) and containing 2% calcium perovskite satisfactorily explains the Nd and Hf isotopic discordance observed for Isua amphibolites. The negative HFSE anomalies characterizing Isua basalts likewise could have been inherited from such an early (4.53-4.32 Ga) deep mantle cumulate. Since the similar to 4 Ga old Acasta Gneisses (Northwest Territories, Canada) have radiogenic ...