Rare Earth Elements in Petrogenetic Studies of Igneous Systems

of melting, the mineralogical and chemical composition of the source during melting, the extent of the melting processes involved, and how the melt is modified by assimilation, metasomatism, differentiation, and fluids. In order to evaluate the im­ portance of each, a detailed knowledge of the geochemistry of systems involving fluids, minerals, and melts would be required. This know ledge, how ever, is not available. Thus, it is necessary to make inf erences based on the inf ormation we have. The development of precise analytical techniques for the analysis of the individual rare earth elements (REE) as well as the development of quantitative trace element modeling using single element distribution coefficients (Kd)l in mineral-melt systems have made the REE particularly valuable for placing limits on the applicability of proposed petrogenetic models. Realizing the great potential of the REE many laboratories have analyzed wide rang es of rock types and determined Kd'S based on natural samples and laboratory experiments. Although