- © The Mineralogical Society Of America
Feldspars are among the most common minerals in the Earth’s crust, and are found in a variety of rock types. Diffusion in feldspars has been studied for well over half a century, with Rosenqvist’s (1949) measurements of Ra and Pb diffusion among the earliest published works. Major efforts in measuring diffusion in feldspars, primarily of the alkali elements, were undertaken in the early 1970s, with the work of Bailey (1971), Lin and Yund (1972), Petrovic (1972), Foland (1974), Giletti et al. (1974) and Kasper (1975). Many of these early studies used bulk-exchange techniques rather than direct depth profiling, or employed methods of limited depth resolution such as serial sectioning; these methods, while state of the art for their time, impose several limitations, including a range of measurement restricted to relatively fast diffusivities, and the difficulty of distinguishing the effects on measured chemical or isotopic compositions that may be a result of diffusional fast paths, surface reaction, and/or other artifacts, from those contributions due solely to volume diffusion. Development of high-resolution depth profiling techniques, such as SIMS and RBS, have permitted measurement of much smaller diffusivities for a broader range of elements, and reduced some of the uncertainties characteristic of bulk-exchange methods.
Feldspar diffusion data have been previously summarized in Yund (1983) and Smith and Brown (1988), and were included in Brady’s (1995) compilation of diffusion data for silicate minerals. Since the publication of these works, there have been numerous diffusion studies of feldspars encompassing a range of compositions in alkali feldspars and across the plagioclase series. These have included measurements of diffusion of major elements Na, K, Ca, Ba, oxygen and silicon, as well as Na-K and CaAl-NaSi interdiffusion, diffusion of noble gases, and diffusion of minor and trace elements including Fe, Mg, Sr, …