Geochemistry of enclaves and host granites from the Nelas area, central Portugal

Abstract

Tonalitic, granodioritic and monzogranitic enclaves occur in the Hercynian peraluminous porphyritic biotite granite and biotite-muscovite granite from the Nelas region. Some variation diagrams show linear trends, but others show dispersion. The enclaves generally have closely similar isotopic signatures to those of the host granites. They contain xenocrystic plagioclase with the same composition as phenocrysts of the host granite, and have biotite as the sole ferromagnesian phase with a composition typically similar to that of the host granite. However, some cores of enclaves have biotite slightly chemically distinct from that of rims. The modelling of major and trace elements of granodioritic enclaves and hybrid host granite indicate that they result from simple mingling/mixing between a tonalitic magma and the host granite magma. Microgranular enclaves are thus interpreted to be globules of a more mafic magma probably from an enriched mantle source. Partial equilibration has been achieved between these enclaves and the host granite.