Sulfide saturation in alkaline to peralkaline igneous rocks.

• Applicant: Privatdozent Dr. Michael Marks
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 271894046

The behavior of sulfur in silicate melts is a widely discussed topic: Its release during volcanic eruptions affects the global climate, and the sulfur content of magmas exerts a major control on the genesis of magmatic to hydrothermal ore deposits. Primary sulfides (mainly pyrrhotite, chalcopyrite and molybdenite) and other sulfur-bearing minerals (mainly apatite and sodalite group minerals) in mafic, intermediate and granitic systems have been the focus of many recent studies, but no detailed and systematic study on this topic in alkaline to peralkaline magmatic systems has been undertaken so far.The present proposal investigates and compares the primary sulfide inventory of two otherwise well-characterized alkaline to peralkaline plutonic complexes (Tamazeght in Morocco and Ilimaussaq in Greenland) and their spatially associated and genetically related dyke rocks. The rocks to be investigated cover a large compositional diversity ranging mainly from gabbroic (alkali basaltic) via monzonitic (latitic) and syenitic (trachytic) to nepheline syenitic (phonolitic) compositions. Therefore, the results of this study will have general implications for the behavior of sulfur in alkaline to peralkaline magmatic systems. The various sulfides will be analyzed for their major, minor and trace element composition and their sulfur isotopic composition in order to track their compositional evolution during magmatic differentiation. These data will be combined with determination of sulfur concentrations in other sulfur-bearing minerals (apatite and sodalite) and with compositional data on co-existing Fe-Mg silicates and Fe-Ti oxides, since this provides important constraints on prevailing oxygen and sulfur fugacity during their formation. The sulfur isotope composition of the sulfides will provide constraints on the sulfur isotope composition of the magmas and the temperature of crystallization of the different sulfide assemblages.The variability within and between the two complexes is expected to reveal detailed insights into magma chamber processes (e.g., sulfide-silicate melt separation, fractional crystallization, magma recharge, formation of magmatic layering) and will decipher the influence of sulfide formation on the geochemical evolution of alkaline to peralkaline magmas with possible implications for the ore potential of such systems. The comparison between plutonic rocks and dyke rocks will provide detailed insight into potential differences with respect to the retention and alteration of the primary chemical and isotopic compositions of sulfides related to different cooling rates and the intensity of hydrothermal overprint.

• DFG Programme: Research Grants
• Cooperation Partner: Professor Dr. Michael Wiedenbeck