Terrestrial 107Pd-107Ag Systematics: Implications for Mantle Circulation, Core-Mantle Exchange and the Age of the Earth

Carnegie Institution Of Washington, Washington DC

Investigators

Abstract

0229417 Hauri Using funds from this grant to the Carnegie Institution of Washington - Department of Terrestrial Magnetism, analyses of the Ag concentration and isotopic composition of a wide variety of terrestrial (mid-ocean ridge basalts, ocean island basalts, Archean komatiites, fertile mantle peridotite xenoliths, and assorted crustal rocks) and extraterrestrial (primarily whole rock chondrites) materials will be undertaken in order to explore the possibility that the 107Pd/107Ag radiometric system can be used to reveal the detailed chronology of Earth formation and the separation of its core from the mantle. 107Pd decays to 107Ag with a half-life of 6.5 Myr. The Pd-Ag isotope system is thus sensitive to events occurring only during the first 60 Myr of solar system history. A new MC-ICPMS analytical technique for Ag isotopic determinations, developed by the PI's, allows a factor of 10-20 improvement in isotope ratio precision compared to previously utilized approaches. If variations in Ag isotopic composition are observed that can be related to 107Pd decay, then Earth must have experienced significant geochemical differentiation within 50-60 Myr of solar system formation. Alternatively, if the observed Ag variation is due only to mass fractionation, then the volatile-element depletion of Earth, and terrestrial core formation, must have occurred >60 Myr after solar system formation. A post-doctoral associate will be employed and trained to assist with continued development of the chemical and mass spectrometric procedures for Ag isotopic analysis, and will assist us in disseminating this particular technique, and other new techniques for isotope analysis by ICP-MS, to the broader earth science community.