Calcium isotope fractionation between silicate minerals and melts

• Applicant: Privatdozent Dr. Nikolaus Gussone
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 343559710

Geochemical signatures that originate from mass dependent Ca isotope fractionation have been established as proxies for low temperature applications, like oceanic Ca budget reconstructions, trophic level indicators, nutrient cycling in soils or biomineralisation processes. In high temperature systems, mass dependent Ca isotope fractionation has been considered small for a long time, but recent findings on natural silicate rocks and minerals as well as lab experiments, suggest significant stable isotope fractionation between silicate minerals. While current conceptual models favor crustal recycling as mechanism for creating Ca isotope variability in different igneous rocks, the potential role of partial melting and fractional crystallization is not equally considered. In this project we will identify Ca isotope trends in natural igneous rocks and mineral/melt partitioning experiment. To study systematics of melting, crystallisation and mantle sources, we will investigate ocean island basalts from different hotspots, different source regions and degrees of partial melting. Calcium isotope fractionation within a magma chamber will be studied on a volcanic sequence, to characterise the evolution of the Ca isotope composition of the melt during fractional crystallisation of Ca bearing minerals. We aim to study the mass dependent Ca isotope fractionation between garnet, clinopyroxene and melts, as garnet and clinopyroxene are the mineral phases which dominate the Ca budget of partial mantle melts. To quantify the fractionation between minerals and melts, we plan to conduct melting experiments at different pressure and temperature conditions. As a synthesis, we will develop a model to describe Ca isotope fractionation processes during magmatic processes, e.g. partial melting and fractional crystallisation.

• DFG Programme: Research Grants
• Cooperation Partners: Dr. Jasper Berndt-Gerdes; Professor Stephan Klemme, Ph.D.; Dr. Arno Rohrbach; Professor Andreas Stracke, Ph.D.