Halogene und Halogenisotope in magmatischen Systemen
Zusammenfassung der Projektergebnisse
This project was a first systematic study on halogen (F, Cl, Br, I) distribution and halogen isotope fractionation in magmatic systems, focussing on Cl and Br. The study investigated peralkaline rocks as these are halogen-rich and contain abundant sodalite- (SGM) and eudialytegroup minerals (EGM), the major Cl and Br carriers in peralkaline magmatic systems. As a start, four well-characterized localities (Ilímaussaq in Greenland, Khibina in Russia, Tamazeght in Morocco, and Norra Kärr in Sweden) were investigated. Besides being typically Cl-rich, SGM (about 7 wt.% Cl) and EGM (up to 1 wt.% Cl) may contain up to 200 µg/g and 30 µg/g Br, respectively and up to about 0.5 wt.% of F. Iodine is however generally low (largely <<1µg/g). It could be demonstrated that Cl and Br may be fractionated from each other during orthomagmatic differentiation and the relative amounts and timing of SGM and EGM fractionation have a major impact on the Cl/Br evolution of residual melts. The data further show that similar to apatite fractionation in metaluminous rocks, sodalite fractionation in peralkaline rocks causes decreasing Br/Cl in evolved rocks, with generally decreasing Br and Cl contents, while F increases. This project was also a first systematic study on the behaviour of Cl and Br stable isotopes in magmatic systems and investigated the suitability of these isotope systems for deciphering magmatic and hydrothermal processes, including fractional crystallization and fluid exsolution/degassing. The obtained data allowed for estimating Cl isotope fractionation between minerals, melts and fluids and shows how magmatic differentiation and subsequent hydrothermal activity causes significant Cl-isotopic heterogeneity within a given plutonic complex. The obtained data for Ilímaussaq was used to estimate the Cl-isotopic composition of the parental mantle-derived melt to +0.3‰, which may be representative for the lithospheric mantle below South Greenland. The Br isotope data suggests negative mineral-melt Br isotope fractionation for sodalite allowing the first time to constrain a Br isotopic composition of a mantle-derived melt to a value of +0.5 to +0.6‰ relative to SMOB.
Projektbezogene Publikationen (Auswahl)
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Changes in Halogen (F, Cl, Br, and I) and S Ratios in Rock-Forming Minerals as Monitors for Magmatic Differentiation, Volatile-Loss, and Hydrothermal Overprint: The Case for Peralkaline Systems. Minerals, 10(11), 995.
Eggenkamp, Hans G.M.; Marks, Michael A.W.; Atanasova, Petya; Wenzel, Thomas & Markl, Gregor
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Bromine Isotope Variations in Magmatic and Hydrothermal Sodalite and Tugtupite and the Estimation of Br Isotope Fractionation between Melt and Sodalite. Minerals, 11(4), 370.
Eggenkamp, Hans G. M.; Marks, Michael A. W.; Louvat, Pascale & Markl, Gregor
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Cl isotope fractionation in magmatic and hydrothermal eudialyte, sodalite and tugtupite (Ilímaussaq intrusion, South Greenland). Chemical Geology, 604, 120932.
Eggenkamp, H.G.M.; Marks, M.A.W.; Bonifacie, M.; Bardoux, G.; Agrinier, P. & Markl, G.
