Program > Browse abstracts by speaker > Terranova Kevin Gabriele

Fe-Mg interdiffusion in clinopyroxenes (cpx) is crucial for constraining magmatic, metamorphic, and planetary timescales, such as cooling rates of rocks from the Moon and Mars. For these applications a calibration of Fe-Mg interdiffusion in Fe-rich cpx is required. This study aims to extend the pre-existing data for DFe-Mg and address the effect of Fe in cpx through controlled experiments following a new approach developed for orthopyroxene. Gem-quality cpx crystals with a Di90Hed10 composition were oriented parallel to the [001] axes and coated by pulsed laser deposition with Fe-rich-thin-films (0.5-1 µm thick) as diffusion reservoir. We have used three different compositions as targets for the thin film production - olivine [(Fe0.5,Mg0.5)2SiO4], orthopyroxene [(Fe0.5,Mg0.5)2Si2O6], and clinopyroxene [Ca(Fe0.5,Mg0.5)Si2O6]. The objective was to identify the ideal source for subsequent diffusion annealing experiments. In our first annealing experiments the three types of diffusion couples were simultaneously heated in vertical gas-mixing furnaces at 1105 °C and 1150 °C at atmospheric pressure and the same logfO₂ = -11 bar. We prepared lamellae from the diffusion couples and reference samples using focused ion beam thinning and they were analyzed using Backscattered Electron Imaging (BSE) and Energy-Dispersive X-ray (EDX) mapping at low acceleration voltages. Concentration profiles with lengths of a few µm were extracted from EDX maps and deconvolved using reference sample data. During annealing, the films crystallized into a polycrystalline layer. For olivine and orthopyroxene films we observe crystals averaging ~200-300 nm, which is responsible for a substantial topography and interface irregularity. For the clinopyroxene thin film, crystallization led to the formation of clinopyroxene, wollastonite, and Fe-bustamite. By comparison with the reference samples we did not resolve any effect of Fe-Mg interdiffusion into the Cpx crystal of the annealed samples, which hints at slower diffusion rates for Fe-Mg in Fe-rich cpx than those predicted from previous studies.