Wed 23rd September @ 12 pm, Rm 312.222

Abstract

Pb isotope system is a powerful tool that played a significant role in emergence of current understanding of differentiation and evolution of the Earth. Since initial recognition that variability of Pb isotope compositions in many rocks can be linked to the existence of several planetary scale reservoirs, Pb data have been used in combination with other isotope systems to develop modern field of mantle geodynamics that links major chemical features of the Earth in the frame work of plate tectonics model. One significant question that remains mostly unresolved is timing and mechanism of initial differentiation that formed existing global reservoirs on the planet.

In contrast to the terrestrial Pb evolution models, development of similar constraints for Mars was stalled by an extended argument about Pb-Pb ages of Martian meteorites, while on the Moon they have been hindered by very radiogenic Pb composition of lunar materials and persisting laboratory contamination.

Our recent SIMS work on some Martian meteorites and lunar basalts indicates a possibility to overcome some of these problems. Several distinct reservoirs on Mars and Moon can be characterized with respect to their Pb isotope variations and some initial conclusions about the timing of their formation can be made based on the small initially collected data set. Some of this data also allow reevaluation of current ideas about initial stages of differentiation that formed diversity of major terrestrial reservoirs.