Geoquímica de granitóides de Pera Velha - Vila Nova de Paiva - Ferreira de Aves

Abstract

Os granitoides variscos peraluminosos que afloram na area de Pera Velha . Vila Nova de Paiva . Ferreira de Aves intruiram metassedimentos do Complexo Xisto-Grauvaquico Cambrico, Ordovicico e Carbonico. A sua instalacao esta relacionada com a 3a fase de deformacao da orogenia hercinica (D3). O granodiorito a monzogranito levemente porfiroide biotitico-moscovitico de Lagares, de 317 Ma de idade, e sin-D3, enquanto o monzogranito biotitico-moscovitico de Pera Velha, de 295 Ma, e o monzogranito-sienogranito porfiroide biotitico-moscovitico de Ferreira de Aves, de 292 Ma sao tardi- a pos-D3. As composicoes geoquimicas dos tres granitoides e os diagramas de variacao para elementos maiores e menores das rochas, biotites e moscovites indicam que nao estao relacionados, o que e apoiado pela interseccao dos perfis de terras raras dos tres granitoides nas terras raras pesadas. As composicoes quimicas de plagioclase, turmalina e apatite tambem mostram evidencias de que os tres granitoides nao estao relacionados. O monzogranito-sienogranito de Ferreira de Aves evoluiu por cristalizacao fraccionada de quartzo, feldspato potassico, plagioclase, biotite e ilmenite. Os dados isotopicos (87Sr/86Sr)i, ƒÃNdi e ƒÂ18O indicam que os tres granitoides terao resultado da fusao parcial de material dominantemente da crusta continental superior, embora outros processos possam estar envolvidos. As caracteristicas dos tres granitoides sao dominantemente do tipo S.

The peraluminous Hercynian granitoids from the Pera Velha – Vila Nova de Paiva – Ferreira de Aves area intruded metasediments of the Cambrian schist-greywake complex, Ordovician and Carboniferous. Their emplacements are related to the third Hercynian deformation event (D3). The slightly porphyritic biotite-muscovite granodiorite-monzogranite from Lagares is 317 My old and syn-D3, while the biotite-muscovite monzogranite from Pera Velha (295 My) and the porphyritic biotite-muscovite monzogranite-syenogranite from Ferreira de Aves (292 My) can both be included in the group of late- to post-D3 granitoids. The geochemical compositions and the major and trace element variation diagrams for the three granitoids, biotites and muscovites, suggest that they are not related, which is supported by the REE patterns, that intersect each other in the HREE. Plagioclase, tourmaline and apatite compositions also give evidence that the three granitoids are not related. The Ferreira de Aves monzogranite-syenogranite evolved by fractional crystallization of quartz, K-feldspar, plagioclase, biotite and ilmenite. The (87Sr/86Sr)i, εNdi and δ18O isotopic data suggest that these three granitoids were mainly originated by partial melting of upper crustal sources, but do not exclude the contribution of other source components. The characteristics of the three granitoids point to an S-type origin.