- © The Mineralogical Society Of America
Diffusion in general is such a widespread phenomenon in nature that a basic knowledge can serve very effectively to address well known applications not only to thermochronology and petrology, but also to environmental geology (e.g., paleoclimate), sedimentology, and applied geosciences (e.g., assessing contamination of gas stations). Indeed, the list of potential applications of diffusion phenomena is so long that an exhaustive treatment would quickly exceed the scope of this review. The reader is therefore referred to reviews covering various aspects of diffusion in the Earth sciences, including diffusion in melts (Watson 1994; Chakraborty 1995), diffusion processes during diagenesis (Berner 1980; Krom and Berner 1980; Boudreau 2000) and diffusion phenomena in general (e.g., Lasaga 1998; Ganguly 2002; Watson and Baxter 2007; Zhang 2008). All of these treatments are based on the same general concepts of diffusion, which do not need restating here in great detail. Applications of diffusion profiles in igneous systems have been thoroughly reviewed a recent Reviews in Mineralogy and Geochemistry volume (RiMG 69 – Putirka and Tepley 2008) and there is also an excellent volume on low temperature thermochronology (RiMG 58 – Reiners and Ehlers 2005) describing the impact and application of diffusion theory for age and thermal history determination. With these precedents in mind, we focus the present review on the application of diffusion in high temperature regimes (i.e., systems at T > 500 °C). Both igneous and metamorphic systems are addressed, but because of the recent precedents noted above, we emphasize recent developments and challenges in metamorphic studies.
In a broad sense, diffusion describes the statistical, non-directional movement of molecules (or heat) through a medium of interest. As independent theories of diffusion were developed in the early 19th century and compared with the principles of statistical variance, it was …