No abstract

International audienceThe studied tonalitic and trondhjemitic granulites are located in the SSE granulitic domain of the São Francisco craton, Bahia, Brazil, where they represent most of the southern part of the Archean and Paleoproterozoic Itabuna-Salvador-Curaçá Block (ISCB). Chemically, the tonalitic and trondhjemitic granulites belong to a low-K calc-alkaline suite; their REE patterns are steep with strong LREE/HREE fractionation and no significant Eu anomaly. Garnet-bearing mafic granulites that occur as enclaves in the tonalitic and trondhjemitic granulites were derived from basalts and/or gabbros of tholeiitic affinity. Geochemical modelling showed that the tonalitic and trondhjemitic granulites were produced by moderate fractional crystallization of an assemblage of hornblende and plagioclase, with subordinate amounts of magnetite, apatite, allanite and zircon. The garnet-bearing mafic granulites would be the source of the magmas that generated these rocks. Partial melting left a residue made up of plagioclase, garnet, orthopyroxene and hornblende

Peraluminous granitoids were recently mapped in the Rio Piranhas-Seridó Domain, the northeast portion of the Borborema Province. These bodies occur as stock and intrusive dikes in the metapelites of the Seridó Formation, constituting the Jardim do Seridó Suite. This suite has two facies. The first and most expressive facies consists of a medium-grained and whitish leucocratic monzogranite with muscovite, garnet, and biotite, while the second is represented by fine-grained and greyish leucocratic granodiorites with biotite, cropping out mainly on the edges of the main body. The thermobarometric conditions for the crystallization of the monzogranites were estimated between 2-5 kbar and 690-950 ºC, whereas the lithochemical data indicate a syn-collisional peraluminous signature. Neoproterozoic garnet-biotite schist xenoliths of the Seridó Formation are sometimes observed partially assimilated in the main body (stock). A U-Pb zircon age of 592 ± 2 Ma obtained in the main body is considered as the crystallization age of the Jardim do Seridó Suite, corroborating the proposed existence of peraluminous magmas associated with the Brasiliano Orogenesis in the Rio Piranhas-Seridó Domain. The chemical and petrographic data identified this suite as fertile to that it can generate dikes of rare elements-bearing pegmatites.

No abstract