20-EPN2-033: An experimental study of bromine partitioning between olivine, orthopyroxene and silicate melt

20-EPN2-033: An experimental study of bromine partitioning between olivine, orthopyroxene and silicate melt

Visit by Bastian Joachim-Mrosko, University of Innsbruck (Austria) to TA2.15 ETH Zurich Geo- and Cosmochemistry Isotope Facility (Switzerland).
Dates of visit: 04-18 February 2022 and 13-21. April 2022

Report Summary: The heavy halogens are excellent tracers for volatile transport processes in the Earth’s mantle. Our understanding of their budget and distribution is, however, very limited due to their extremely low abundances in the most abundant upper mantle minerals and a lack of well-defined partition coefficients that describe their behaviour during partial melting of the Earth’s mantle.

In this project, we analysed the bromine concentration in minerals and melts of samples, which were produced during high-P-T experiments that simulated partial melting of the Earth’s mantle at Mid-Ocean-Ridge-Basalt and Ocean-Island-Basalt source regions. For this, the neutron irradiation technique was applied, which produced 80,82Kr from 79,81Br. This technique results in unmatched detection limits below the ppm-level for the determination of bromine concentrations in nominally anhydrous minerals. During the analysis, regions of interest in the respective samples were ablated with a UV-VIS-Laser at a 10s of micrometer scale. Afterwards, the noble gases were separated and analysed with the “Albatros” mass spectrometer at ETH Zürich. This allowed us to determine bromine concentrations in the melt and in individual olivine and orthopyroxene crystals.First results show that bromine indeed behaves very incompatible with first estimates of bromine partition coefficients between minerals and melt being well below 10-3. In addition, olivine seems to be the main carrier for the heavy halogens in the Earth’s upper mantle.


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