AbstractsEarth & Environmental Science

Iron Isotope Cosmochemistry

by Kun Wang




Institution: Washington University in St. Louis
Department:
Year: 2013
Keywords: Asteroids; Cosmochemistry; Fe isotope; Isotope Geochemistry; Meteorites; Moon; Earth Sciences
Record ID: 2019048
Full text PDF: http://openscholarship.wustl.edu/etd/1189


http://openscholarship.wustl.edu/cgi/viewcontent.cgi?article=2189&context=etd


Abstract

Iron is the most abundant element in the Earth and the 4th most abundant in the crust and mantle; Fe is involved in every stage of planetary formation and differentiation. Iron isotope ratios are robust process tracers used to understand the origin of the Solar System, planetary formation, and differentiation processes such as the moon-forming giant impact, core-mantle segregation, and crust formation. In this dissertation, I report the most complete dataset of high-precision iron isotope compositions of a wide range of extraterrestrial samples including carbonaceous, ordinary, and enstatite chondrites, aubrites, brachinites, HED meteorites: howardites, eucrites and diogenites), martian meteorites, angrites, lunar meteorites, lunar regolith and ungrouped meteorites. I discuss iron isotope fractionations among these extraterrestrial materials in term of solar nebular processing, asteroidal parent-body processing, planetary differentiation: core-mantle differentiation and crust formation), magmatism, and planetary surface processing. In Chapter 1, I introduce some basic knowledge about the meteorites and lunar samples, which comprise the research objectives in following chapters. In addition, the general concepts of the nucleosynthesis of Fe isotopes and mass-dependent Fe isotope fractionation mechanisms are also discussed. At last, I review the technique of high precision isotopic analyses of iron using anion-exchange chromatography and MC-ICP-MS. In Chapter 2, I focus on the non-mass-dependent fractionation of Fe isotopes and examine the possible isotopic anomalies in some of the oldest meteorites in the Solar System, which could help in understanding the stellar building blocks of our Solar System. The solar nebula was made of materials from the nucleosynthesis of older generation stars. The solar nebula was initially thought to have been chemically and isotopically well mixed. However, since late 1960s, isotopic anomalies have been observed in both bulk meteorite and mineral scales. These isotopic anomalies are relic signals of the original building blocks of our Solar System, surviving from the mixing of early solar nebula. With the instrumental advances such as the application of MC-ICP-MS, smaller and smaller scale isotopic anomalies can be identified in meteorite samples. By looking at these anomalies, we could acquire information about the original building blocks of our Solar System. I reexamined the 54Cr anomalies: discovered in the 1980s and for which the origin is still debated) by investigating the collateral effects on 58Fe nuclide. These neutron-rich nuclides are expected to be produced together in Type II supernovae or Type Ia supernovae. Even though these 54Cr anomalies have been long observed, the carrier phases and the stellar origin had not been identified until our research. By measuring 58Fe, I put constraints on the nucleosynthetic origins: most probably Type II supernovae). From Chapter 3 to 7, I emphasize mass-dependent fractionations of Fe isotopes. First, in Chapter 3, I present the most…