Trace element incorporation in minerals and melts
Published:January 01, 2001
Neil L. Allan, Jon D. Blundy, John A. Purton, Mikhail Yu. Lavrentiev, Bernard J. Wood, 2001. "Trace element incorporation in minerals and melts", Solid Solutions in Silicate and Oxide Systems, Charles A. Geiger
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A primary goal of geochemistry is the understanding of natural chemical differentiation through the chemical analysis of geological materials. Of particular interest to the geochemist are trace elements (i.e. those present at concentrations of less than 0.1% by weight) which behave essentially as passive tracers during differentiation, and whose distribution can therefore yield process-specific information. Interpreting and modelling trace-element data requires quantitative information on how elements partition between coexisting phases, such as minerals and melts. Partitioning in turn depends on the energetics of trace-element incorporation into minerals and melts. With the advent of new analytical techniques and enhanced computer power our understanding in this field has increased substantially over the last two decades, to the extent that we can now offer greatly enhanced interpretative and modelling tools for the trace element geochemist. In this chapter we will attempt to summarise the state-of-the-art, with particular emphasis on new computational approaches. We begin by outlining experimental and analytical methods of investigating partitioning, delineate the principal controls on element partitioning, and discuss simple lattice strain models of trace element incorporation into minerals. The rest of the chapter is devoted to the development of atomistic computer simulation techniques and their application to the problem of trace element incorporation. The extent to which these approaches can reproduce the experimental observations is evaluated. Our focus is high-temperature silicate mineral-melt or mineral-mineral partitioning of trace cations, although our findings can be generalised to lower temperatures and non-silicate fluids and anions.
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Solid Solutions in Silicate and Oxide Systems
The EMU book series or notes, as they are called, were introduced to provide university teachers with up-to-date reviews in important, rapidly evolving areas of mineralogy, petrology and geochemistry. They are also meant to introduce scientists into special and often interdisciplinary fields of research. In this regard, a volume on solid solutions is current and sorely needed. The solid Earth, as well as many meteorites and the other solid planets, consists for the most part of mineral solid solutions. Research on solid solutions is extremely broad encompassing work in physics and chemistry, metallurgy, materials science and, last but not least, mineralogy and petrology. Hence, because the theme is so strongly interdisciplinary in nature, the workshop was organised to include solid state physicists, physical chemists, crystallographers, mineralogists and petrologists. The various chapters reflect some of this diversity and show what mineralogy has become. Experimental investigations in mineralogy now routinely include different types of spectroscopies along with more traditional phase equilibrium, X-ray diffraction, calorimetry, and TEM methods. There have also been new and impressive developments in theory and computation. Many computational approaches relating to the study of solid solutions, for example, the Cluster Variation Method or Monte Carlo simulations, have been brought in from materials science, chemistry and physics. It can be concluded that the traditional or historical, and perhaps artificial, boundaries between the various disciplines are disappearing. Many current research efforts in mineralogy are similar to those in chemistry, materials science and physics.