Chlorine isotope fractionation in alkaline magmatic systems

• Applicant: Privatdozent Dr. Michael Marks
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450099520

This project represents a systematic study to constrain the behaviour of the Cl isotope system in alkaline magmatic to hydrothermal systems and the Cl isotope heterogeneity in the mantle. Because of their general derivation from lithospheric mantle sources and their halogen-rich nature, alkaline rocks are important to understand halogen transport from the mantle into the crust and halogen budgets during emplacement, differentiation, and fluid exsolution/degassing of magmatic systems. The extensive sample collection to be worked with includes plutonic, volcanic and metamorphosed alkaline rocks from more than 40 localities worldwide.Based on our preliminary data, the following three hypotheses will be tested during this project: (i) Magmatic processes, such as fractional crystallization and fluid exsolution/ degassing cause fractionation of stable Cl isotopes (ii) Heterogeneity of the mantle with respect to Cl isotope compositions is recorded in alkaline magmas (iii) Deformation and fluid-rock interaction during metamorphism of alkaline rocks does not significantly change their Cl isotopic composition. The project will use Cl isotope data (ICP-MS, SIMS), halogen (F, Cl, Br, I) and S concentration data (EPMA, CIC) as well as O and S isotope data on mineral separates. Combined with mass balance and Rayleigh-type calculations, this will allow to (i) develop applications of Cl isotope data for deciphering magmatic to hydrothermal processes and (ii) to constrain global compositional heterogeneities in the (lithospheric) mantle with respect to halogen ratios (e.g., F/Cl, Cl/Br, Cl/I) and Cl isotope compositions, for which already evidence was presented.

• DFG Programme: Research Grants
• International Connection: France, Switzerland, United Kingdom
• Cooperation Partners: Dr. Pierre Agrinier; William Hutchinson, Ph.D.; Professor Dr. Torsten Vennemann