4 - Using Trace Element Data

Summary

The behaviour of trace elements in geochemistry may be understood in terms of the chemical properties of their ions and the way in which they are partitioned between solid (mineral) and melt phases during the melting and solidification of igneous rocks and their sources. However, partition coefficients vary according to a large number of physical parameters such as temperature, pressure, melt composition and oxygen fugacity, and these effects can be modelled using the results of experimental petrology and thermodynamic analysis. Trace element data for both igneous and sedimentary rocks are plotted according to their geochemical properties and may be displayed on bivariate diagrams, rare earth element (REE) plots, multi-element plots normalised to the composition of the Earth’s primitive mantle or as highly siderophile elements (HSE). The physical understanding of trace element distributions means that they can be modelled during partial melting, fractional crystallisation and assimilation and comparisons made with the measured compositions of natural rock samples.