Origin and age of the Eisenkappel gabbro to granite suite (Carinthia, SE Austrian Alps)

摘要

The northern part of the Karawanken plutonic belt is a gabbro-granite complex located just north of the Periadriatic lineament near the Slovenian-Austrian border. Petrographie and geochemical studies of the Eisenkappel intrusive complex indicate that this multiphase plutonic suite developed by a combination of crystal accumulation, fractional crystallization and assimilation processes, magma mixing and mingling. The mafic rocks are alkaline and have within-plate geochemical characteristics, indicating anorogenic magmatism in an extensional setting and derivation from an enriched mantle source. The mafic melts triggered partial melting of the crust and the formation of granite. The granitic rocks are alkalic, metaluminous and have the high Fe/Fe + Mg characteristics of within-plate plutons. Temperature and pressure conditions, derived from amphibole-plagioclase and different amphibole thermobarometers, suggest that the analysed Eisenkappel gabbros crystallized at around 1000±20°C and 380-470 MPa, whereas the granitic rock crystallized at T<800 ± 20 °C and <350 MPa. Mineral-whole rock Sm-Nd analyses of two cumulate gabbros yielded 249 ± 8.4 Ma and 250 ± 26 Ma (sNd: +3.6), garnet-whole rock Sm-Nd analyses of two silicic samples yielded well-constrained ages of 238.4±1.9Maand242.1±2.1 Ma(εNd: -2.6).