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

利用这笔赠款给华盛顿卡内基研究所地磁系的资金，将对各种陆地(大洋中脊玄武岩、洋岛玄武岩、太古宙科马提岩、富饶的地幔橄榄岩包体和各种地壳岩石)和地外(主要是全岩球粒陨石)材料的银浓度和同位素组成进行分析，以探索107Pd/107Ag辐射测量系统可用于揭示地球形成的详细年代学及其核心与地幔分离的可能性。~(107)Pd衰变到~(107)Ag，半衰期为6.5Myr。因此，Pd-Ag同位素系统只对太阳系历史的前60Myr期间发生的事件敏感。一种新的用于银同位素测定的MC-ICPMS分析技术，由国际标准化组织开发，与以前使用的方法相比，同位素比精度提高了10-20倍。如果观察到与107Pd衰变有关的银同位素组成的变化，那么在太阳系形成的50-60Myr范围内，地球肯定经历了显著的地球化学差异。或者，如果观测到的银的变化仅仅是由于质量分馏，那么地球的挥发性元素的枯竭和地核的形成，一定发生在太阳系形成后60Myr。将雇用和培训一名博士后助理，以协助继续开发银同位素分析的化学和质谱学程序，并将协助我们向更广泛的地球科学界传播这项特殊技术以及电感耦合等离子体质谱仪进行同位素分析的其他新技术。

0229417HauriUsing 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.