QUANTITATIVE MEASUREMENT OF SHORT COMPOSITIONAL PROFILES USING ANALYTICAL TRANSMISSION ELECTRON-MICROSCOPY

Analytical transmission electron microscopy (ATEM) was used to quantit atively measure sub-micrometer compositional profiles produced experim entally by Fe-Mg interdiffusion experiments in olivine. Although analy sis of minerals by ATEM is common, compositional profiles suitable for quantitative modeling of diffusion are nest generally measured in min erals with ATEM. To demonstrate the suitability of ATEM for diffusion studies in minerals, we have investigated Fe-Mg interdiffusion in expe rimentally annealed olivine. Because the compositional gradients were induced under well-controlled laboratory conditions, the accuracy of t he measurements could be tested by comparing compositional profiles me asured by both ATEM and EMPA as well as by retrieving diffusion coeffi cients from both TER I and EMPA data. The agreement in diffusion coeff icients shows that point defect equilibration in the interfacial regio n of the diffusion couple occurs extremely rapidly at 1200 degrees C. The ability to obtain diffusion data from such short anneals enables v arious experiments that were not previously possible-for example, to s tudy diffusion rates at high pressures where long f(O2) buffered annea ls are not generally feasible. ATEM profile measurement is compared wi th other techniques such as SIMS and RES and some limitations and appl ications of ATEM profile measurements are also discussed.