caa a22 4500 463217098 CHVBK 20180405153200.0 cr unu---uuuuu 170326e20070801xx s 000 0 eng 10.1007/s00269-007-0157-7 doi (NATIONALLICENCE)springer-10.1007/s00269-007-0157-7 Fe-Mg diffusion in olivine I: experimental determination between 700 and 1,200 ° C as a function of composition, crystal orientation and oxygen fugacity [Elektronische Daten] [Ralf Dohmen, Hans-Werner Becker, Sumit Chakraborty] We have determined Fe-Mg diffusion coefficients in olivines from different sources (Nanga Parbat, Pakistan and San Carlos, Arizona, USA) at atmospheric pressure as a function of composition, oxygen fugacity (10−5-10−12Pa) and temperature (700-1200°C) using thin films produced by pulsed laser deposition and RBS to analyze the concentration profiles. We have characterized the nano-scale structure and composition of the thin films annealed at various conditions and shown that the nature of the film (e.g. crystallinity, wetting behavior) depends strongly on the annealing conditions. If these variations are not taken into account in the form of boundary conditions for modeling the diffusion profiles, artifacts would result in the diffusion data. The diffusion coefficients obtained from 75 experiments reveal that (i) between fO2 of 10−5 and 10−10Pa, diffusion along all three principal crystallographic directions in olivine, [100], [010] and [001], are described by a constant activation energy of ∼200kJ/mol, precluding any temperature dependence of diffusion anisotropy and change of mechanism of diffusion at temperatures between 950 and 1200°C, (ii) diffusion coefficients increase with oxygen fugacity at fO2>10−10Pa, with an fO2 exponent that lies between 1/4 and 1/7, and (iii) at fO2 below 10−10Pa, and consequently at temperatures below ∼900°C, diffusion becomes weakly dependent/independent of fO2, indicating a change of diffusion mechanism. Activation energy of diffusion at these conditions is slightly higher, ∼220kJ/mol. The data, including the change of mechanism, are analyzed in terms of point defect chemistry in Part II of this work to derive an equation that allows calculation of diffusivities in olivine over its entire field of stability. Availability of directly measured data at temperatures down to 700°C imply that for the first time diffusion coefficients can be interpolated, rather than extrapolated, for modeling most natural systems. Springer-Verlag, 2007 Olivine nationallicence Diffusion nationallicence Point defects nationallicence Thin films nationallicence Nanostructure nationallicence Pulsed Laser Deposition nationallicence Rutherford Backscattering Spectroscopy nationallicence Mineral kinetics nationallicence Dohmen Ralf Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, 44780, Bochum, Germany aut Becker Hans-Werner Institut für Physik mit Ionenstrahlen, Ruhr-Universität Bochum, 44780, Bochum, Germany aut Chakraborty Sumit Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, 44780, Bochum, Germany aut Physics and Chemistry of Minerals Springer-Verlag 34/6(2007-08-01), 389-407 0342-1791 34:6<389 2007 34 269 https://doi.org/10.1007/s00269-007-0157-7 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s00269-007-0157-7 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Dohmen Ralf Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, 44780, Bochum, Germany aut NATIONALLICENCE 700 1- Becker Hans-Werner Institut für Physik mit Ionenstrahlen, Ruhr-Universität Bochum, 44780, Bochum, Germany aut NATIONALLICENCE 700 1- Chakraborty Sumit Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, 44780, Bochum, Germany aut NATIONALLICENCE 773 0- Physics and Chemistry of Minerals Springer-Verlag 34/6(2007-08-01), 389-407 0342-1791 34:6<389 2007 34 269 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer