info:eu-repo/semantics/article
Petrography and metamorphism of the metasedimentary country-rocks of the Jacurici Valley Chromitite-Hosting mafic-ultramafic complexes, Bahia, Northeastern Brazil
Petrography and metamorphism of the metasedimentary country-rocks of the Jacurici Valley Chromitite-Hosting mafic-ultramafic complexes, Bahia, Northeastern Brazil
Registro en:
10.5327/S1519-874X2001000100002
Autor
Del Lama, Eliane A.
Candia, Maria A. F.
Szabó, Gergely A. J.
Institución
Resumen
This paper deal with on the metasedimentary country-rocks of the chromite-bearing ultramafic rocks that occur in the"Jacurici River Valley Chromium District" northeastern Bahia, Brazil. This region presents a complex geologic-petrologic framework of rocks that were intensely deformed, metamorphosed and transformed by metasomatic processes, making it difficult to interpret their evolutionary/metamorphic record. Although the metasedimentary country rocks have also been affected by such processes, it is possible to distinguish evidence of a previous high-grade metamorphism that affected them. Thermobarometric data for the observed mineralogical associations indicate P-T conditions around 750-800ºC and 7-8 kb for the metamorphic peak, based mainly on the presence of olivine in marbles and the cordierite-garnet-sillimanite-spinel association in aluminous gneisses. Este trabalho enfoca as encaixantes metassedimentares das rochas ultramáficas, portadoras de mineralização de cromita, que ocorrem no nordeste do estado da Bahia. Esta região, conhecida como"Distrito Cromitífero do Vale do Rio Jacurici", apresenta grande complexidade geológica-petrológica com rochas intensamente deformadas, metamorfizadas e transformadas por processos metassomáticos, o que dificulta a interpretação do registro metamórfico/evolutivo dessas rochas. Apesar dos metassedimentos também terem sido afetados pelos processos acima, é possível recuperar registros do metamorfismo de alto grau. Dados termobarométricos indicam condições P-T de 750-800ºC e 7-8 kb, baseados na presença de olivina nos mármores e na associação cordierita-granada-sillimanita-hercinita nos gnaisses aluminosos.