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Li isotope fractionation in magmatic systems: Constraints from in situ 7Li determinations on magmatic minerals by femtosecond-laser ablation-MC-ICP-MS

Leitung:Dr. M. Oeser, Prof. Dr. S. Weyer
Bearbeitung:M. Sc. Lena Steinmann
Förderung durch:DFG

This project aims to investigate the fractionation of stable lithium (Li) isotopes in silicate minerals (i.e. olivine and clinopyroxene) from volcanic rocks in order to gain time information on magmatic processes. Since previous studies indicate (i) that stable isotope fractionation in magmas is largely driven by kinetic effects due to diffusive processes and (ii) that Li is a very fast diffusing trace element in minerals (and melts), one can expect large Li isotope variations, i.e. isotopic zoning, on the mineral scale. Therefore, in situ methods (e.g. laser ablation plasma mass spectrometry) have to be used which allow to performing high-precision isotope analyses with high spatial resolution.

The first objective of this project comprises establishing an analytical routine for in situ Li isotope measurements on clinopyroxene and olivine. As the Li concentration in these silicate minerals is very low (usually a few ppm), such analyses are challenging. However, preliminary tests indicate that the analytical setup (femtosecond-laser ablation-multi collector-ICP-MS) available at the Institut für Mineralogie in Hannover is capable of in situ isotope measurements of trace elements in crystals.

After an analytical routine for in situ Li isotope measurements has been established, the second part of this project will focus on the investigation of Li isotopic zoning in chemically zoned clinopyroxene and olivine crystals in volcanic rocks in order to address the following questions:

(a) Is the Li concentration zoning commonly coupled with Li isotopic zoning?

(b) Which (volcanic) processes are recorded by such zoning?

(c) Can we obtain time information (durations) on these processes by using the observed intra-mineral zonations for diffusion modeling?

(d) What are the spatial scales of Li diffusion in magmatic systems – within or beyond hand-specimen scale?

(e) how is Li chemical and isotopic zoning coupled to that of other cations, including Fe and Mg