The abundances of siderophile and highly mobile elements will be used to investigate the accretion of the Earth and the separation of the Earth's core and crust from the Earth's mantle. Well characterized samples from different geochemical reservoirs will be analyzed by neutron activation analysis and inductively coupled plasma mass spectrometry for the moderately siderophile and chalcophile trace elements Mo, W, As, Sb, and Pb and later for the platinum group elements. The formation of the continental crust, involving the extra enrichment of highly mobile elements including Pb, Cs, As, Sb, and W, will be extended by analysis of a large suite of the Earth's oldest known rocks from Canada. Crust formation processes will be studied in suites of volcanic arc rocks for which data on other highly mobile elements are available, especially 10Be. The possible origin of hot spot plumes from near the core-mantle boundary will be addressed by a study of the siderophile element content of samples from both ocean island hot spots and continental flood basalts. The abundances of the siderophile elements in different terrestrial reservoirs will be used to determine the abundances in the bulk silicate Earth. These abundances provide clues to accretion and metal segregation in the mantle, which will be evaluated in quantitative models.
