Petrogenetic links of granitic aplite-pegmatite sills from Gonçalo with granites from Guarda-Belmonte area central Portugal

Resumo

Amblygonite-subtype and lepidolite-subtype (containing petalite) granitic aplite-pegmatite sills from Gonçalo intruded a Variscan granite from Guarda-Belmonte area. Variation diagrams of major and trace elements of four granites and aplite-pegmatite sills, their REE patterns and feldspar compositions indicate that the sills are not related to the host granite, but are related to a sequence defi ned by two biotite>muscovite granites, which is supported by δ18O of whole-rocks and primary muscovite compositions. Least squares analysis of major elements and modelling of trace elements indicate that the youngest biotite>muscovite granite and amblygonite-subtype aplite-pegmatite sills are derived from a biotite>muscovite granite magma by fractional crystallization of quartz, potash feldspar, plagioclase, biotite and ilmenite. Tin and Li enrichments in both amblygonite-subtype and lepidolite-subtype aplite-pegmatite sills are due to fractional crystallization of the same granite magma. The two related granites do not represent crust anomalies in Sn and Li.