Geochemical tracers of mantle processes

Abstract

The mantle can be sampled directly only very rarely. Geochemists have thus come to rely heavily on mantle‐derived magmas to study the composition and evolution of the mantle. Only those compositional features that are unaffected by magmatic processes are useful as tracers of mantle processes. These include radiogenic isotope ratios such as those of He, Sr, Hf, and Os, stable isotope ratios, and ratios of highly incompatible elements or elements of similar incompatibility, such as Ba/Nb or Pb/Ce. The term “incompatible” denotes a preference of the element for a melt over mantle minerals. Highly incompatible elements will partition entirely into the melt under most circumstances, so that the ratio of two such elements in a basalt will be virtually identical to that ratio in its source. This is also true to a lesser degree of ratios such as La/Sm and Zr/Nb, as Zr and Sm are not highly incompatible elements.