| Popis: |
Stable isotope systematics are powerful tools for understanding the evolution history of the earth and Solar system. In this thesis, I present applications of uranium (U) and magnesium (Mg) isotopes in both geochemistry and cosmochemistry. Uranium is a redox-sensitive to the dissolved oxygen level in aqueous environment, and these redox reactions are associated with resolvable isotopic fractionation. Thus, U isotopes are widely used in paleo-environment reconstruction as a proxy of marine anoxia. For this application, the work presented in this thesis includes (1) exploration of the potential of bioapatite as a novel paleoredox proxy. and (2) re-calibrate the U isotope composition of seawater. The U-Pb and Al-Mg systematics provide constraints on the time sequence and composition of the early Solar System. For this application, the work presented in this thesis includes (1) combined Pb-Pb and Al-Mg systematics on calcium-aluminum-rich inclusions (CAIs) to resolve the discrepancies between these two chronometers (2) Al-Mg systematics of bulk CAIs to understand their precursors. This thesis also presents the analytical techniques developed for the studies above and the development of a comprehensive uranium isotope database. |
