Seismological Insights into Heterogeneity Patterns in the Mantle

Both geophysical and geochemical techniques contribute to our understanding of the complex nature of the Earth’s mantle, but the two sources of information provide very different viewpoints. Most geophysical evidence provides an instantaneous snapshot of current structure, whilst geochemical evidence has much more information on age. Further, geophysical probes are naturally integrative since they depend on sampling by finite wavelength disturbances. Geochemical probes increasingly concentrate on detailed insitu analysis of small samples so that they are oriented towards highly localized variations in trace elements (or their isotopes). The mantle represents the silicate shell around the metallic core of the Earth, and much of its properties will inevitably have been strongly influenced by the complex process of accretion of the Earth and the segregation of the core (see, e.g., O’Neill and Palme, [1998]). The major features of mantle structure are presented schematically in Figure 1 with indications of the nature of the geophysical and geochemical evidence used to constrain the behavior. Geophysical conThe State of the Planet: Frontiers and Challenges in Geophyiscs Geophysical Monograph 150, IUGG Volume 19 Copyright 2004 by the International Union of Geodesy and Geophysics and the American Geophysical Union 10.1029/150GM05