Non-traditional stable isotope fractionation during magmatic differentiation: In situ Fe-Mg-isotope analyses of phenocrysts by femtosecond laser ablation MC-ICP-MS

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In this project we aim to investigate the fractionation of non-traditional stable isotopes (i.e. Fe and Mg) of phenocrysts in basalts (olivine, cpx) to improve our knowledge on the temporal evolution of magmatic systems. Our results obtained during the first funding period show that resolving small-scale isotopic variations (i.e. isotopic zoning) in olivines from mid-ocean ridge basalts is feasible by in situ Fe- and Mg isotope analyses using laser ablation plasma mass spectrometry. We are thus able to trace diffusive processes that occur on the mineral scale during magma evolution and to obtain time information by modeling these processes.During the second funding period, we want to apply our developed technique to clinopyroxene phenocrysts in basalts from ocean ridges to address the following questions: (1) Is the zoning of Fe and Mg isotopes in cpx comparable to that observed in olivines and correlated with a chemical zoning? (2) Can we use this zoning to receive time information on magmatic processes? (3) How do the information from cpx compare to the time constraints we have received by modeling of the diffusion zoning in olivine?Additionally, we aim to investigate olivine phenocrysts in basalts from the Shatsky Rise oceanic plateau to gain information on the temporal evolution of magmatic systems with extraordinarily large magma volumes. Finally, we are working on a more general understanding of diffusive fractionation of stable isotopes in crystals by developing a multi-component diffusion model that adequately describes the coupled transport of Fe and Mg isotopes in a crystal.