Abstract :
[en] Diffusion of major and trace elements (e.g. Fe-Mg, Li, etc.) in pyroxene group minerals is a powerful witness and tool to track the timescales of various processes in magmatic systems. Diffusion of volatile elements (e.g. Cu, Li) enable us to estimate timescales of volatile-driven processes. Redox-sensitive elements (e.g. V) may also be used to identify changes, if any, in the redox condition of a magmatic system. The relative variations in diffusion rates between these two groups of elements can provide a complementary record of timescales, as preserved in pyroxenes. In this study, we present preliminary data on diffusion experiments of Li, Cu, and V in gem-quality enstatite (‘Opx-7’) and naturally occurring diopside from Otter Lake, Canada (‘OL-Di’). For Cu and Li diffusion in pyroxenes, we designed an experimental setup in evacuated silica tubes, where two powder-couple diffusion experiments buffered by either NNO or IW solid powder were simultaneously annealed in a muffle furnace at T = 950-1100°C, P = 1 atm for 6-96 hours. For Vanadium diffusion, we used a thin film experiment following [1] in a vertical furnace buffered at log (fO2) = -10 at T = 950-1200°C, P = 1 atm for 66-162 hours. The pyroxene cubes were analyzed using laser ablation ICP-MS (Cu, Li) and Time-of-Flight secondary ion mass spectrometer (V). We find that in addition to Cu, which was deliberately added to the powder as a reservoir, the Otter Lake diopside also acted as a source of Li within the capsule. We propose that the light and volatile lithium diffused out of the diopside and into the Li-poor enstatite. The vacuum seal prevented the volatile Cu and Li from escaping the capsule. We modelled the diffusion profiles from both Opx-7 and OL-Di for Li, Cu, and V to constrain diffusion coefficients. Future directions include investigating the effect of fO2 diffusion for the elements of interest. The results of these studies may be useful to study volatile metal diffusion in magmatic and volcanic systems.
[1] Dohmen R, Becker HW, Meissner E, Etzel T, Chakraborty S (2002). Eur J Mineral 14(6):1155–1168.
