Volume 5, Number 1 – April 2016
Siderophile Elements in Tracing Planetary Formation and Evolution
by Richard J. Walker1
1 Isotope Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD 20742, USA
doi: 10.7185/geochempersp.5.1 | Volume 5, Number 1 (pages 1-145)
The siderophile, or iron-loving elements have many applications in the Earth and planetary sciences. In primitive meteorites, differences in the relative abundances of these elements are likely due to both nebular and parent body processes. In addition, some siderophile elements are also characterised by isotopically distinctive nucleosynthetic signatures. Thus, the relative abundances and isotopic compositions of these elements can be used to trace the genetics of primary planetary building blocks. Although these elements are largely concentrated in the metallic cores of differentiated planetary bodies, their absolute and relative abundances, as well as their isotopic compositions can also reveal important information regarding conditions of core formation and the chemical evolution of the silicate portions of the planetary bodies. The lithophile-siderophile nature of the radiogenic 182Hf-182W system allow it to be used to place chronologic constraints on planetary core formation. The differing incompatibilities of the two elements in silicate systems further mean that the system can also be used to study early differentiation processes and subsequent efficiency of mixing in the silicate portions of differentiated bodies, including Earth.
The abundances of siderophile elements in the terrestrial mantle are used to assess primary and secondary melting processes, and resulting metasomatic interactions. In addition, the Re-Os isotope system can, in some instances, be used to place chronologic constraints on when these processes occurred. The abundances of siderophile elements, and 187Os/188Os and 186Os/188Os ratios in the mantle sources of ocean island basalts can be used to place constraints on the age of recycled materials, and in some instances, the types of recycled materials present in these mantle domains.