Silver isotope variations in chondrites: Volatile depletion and the initial 107Pd abundance of the solar system

Maria Schonbachler, M. Schönbächler, R. W. Carlson, M. F. Horan, T. D. Mock, E. H. Hauri

    Research output: Contribution to journalArticlepeer-review

    Abstract

    The extinct radionuclide 107Pd decays to 107Ag (half-life of 6.5 Ma) and is an early solar system chronometer with outstanding potential to study volatile depletion in the early solar system. Here, a comprehensive Ag isotope study of carbonaceous and ordinary chondrites is presented. Carbonaceous chondrites show limited variations (ε107Ag = -2.1 to +0.8) in Ag isotopic composition that correlate with the Pd/Ag ratios. Assuming a strictly radiogenic origin of these variations, a new initial 107Pd/108Pd of 5.9 (±2.2) × 10-5 for the solar system can be deduced. Comparing the Pd-Ag and Mn-Cr data for carbonaceous chondrites suggests that Mn-Cr and Pd-Ag fractionation took place close to the time of calcium-aluminium-rich inclusion (CAI) and chondrule formation ∼4568 Ma ago. Using the new value for the initial 107Pd abundance, the revised ages for the iron-rich meteorites Gibeon (IVA, 8.5 +3.2/-4.6 Ma), Grant (IIIAB, 13.0 +3.5/-4.9 Ma) and Canyon Diablo (IA, 19.5 +24.1/-10.4 Ma) are consistent with cooling rates and the closure temperature of the Pd-Ag system. In contrast to carbonaceous chondrites, ordinary chondrites show large stable isotope fractionation of order of 1 permil for 107Ag/109Ag. This indicates that different mechanisms of volatile depletion were active in carbonaceous and ordinary chondrites. Nebular processes and accretion, as experienced by carbonaceous chondrites, did not led to significant Ag isotope fractionation, while the significant Ag isotope variations in ordinary chondrites are most likely inflicted by open system parent body metamorphism. © 2008 Elsevier Ltd. All rights reserved.
    Original languageEnglish
    Pages (from-to)5330-5341
    Number of pages11
    JournalGeochimica et Cosmochimica Acta
    Volume72
    Issue number21
    DOIs
    Publication statusPublished - 1 Nov 2008

    Keywords

    • EQUILIBRATED ORDINARY CHONDRITES
    • MULTIPLE-COLLECTOR ICPMS
    • IIIAB-IRON-METEORITES
    • LOW PD/AG METEORITES
    • CARBONACEOUS CHONDRITES
    • TRACE-ELEMENTS
    • PRIMITIVE METEORITES
    • GEOLOGICAL-MATERIALS
    • TERRESTRIAL
    • PLANETS
    • MASS-SPECTROMETRY

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