Petrography and metamorphism of the metasedimentary country-rocks of the Jacurici Valley Chromitite-Hosting mafic-ultramafic complexes, Bahia, Northeastern Brazil

Abstract

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 750-800 degrees C 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.