Chlorisotopen-Fraktionierung in alkalinen magmatischen Systemen
Zusammenfassung der Projektergebnisse
This project built on results of a previous pilot-study and used a unique global data set on halogen concentrations and Cl-isotopic compositions from peralkaline igneous rocks from >40 localities worldwide. 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. This project intended to constrain the behaviour of the Cl isotope system in alkaline magmatic to hydrothermal systems further and to relate these results to potential Cl isotope heterogeneity in the mantle. The data showed a considerable range of Cl-isotopic compositions (d37Cl = -1.9 to +0.7‰). The lowest values derived from hauyne samples from volcanic rocks and showed that volatile degassing may shift Cl-isotopic compositions of the rocks to very light Cl-isotopic compositions. On average, d37Cl values for sodalite tend to be lighter than for eudialyte. This is because of a smaller Cl-isotope fractionation between sodalite and melt compared to eudialyte-melt fractionation. The average d37Cl value for “typical” peralkaline melts is about +0.1‰, with a possible range between about -0.2 to +0.4‰, which compares with earlier determined average d37Cl mantle values of -0.2±0.3‰. However, keeping in mind the variation observed within the previously studied Ilímaussaq complex, the data may still indicate that large Cl isotope heterogeneities exist within the mantle sources for such rocks, which questions the validity of using a general average Cl isotope ratio when Cl isotope mantle values are discussed.
Projektbezogene Publikationen (Auswahl)
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Intragranular halogen (F, Cl, Br), S and δ37Cl variability as determined by SIMS in sodalite and eudialyte from the Ilímaussaq intrusion, South Greenland. Geokarlsruhe 2021
Eggenkamp, H.G.M., Marks, M.A.W., Ludwig, T. & Markl, G.
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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.
