A GEOLOGIA ENTRE MACAÚBAS E CANATIBA (BAHIA) E A EVOLUÇÃO DO SUPERGRUPO ESPINHAÇO NO BRASIL ORIENTAL

Abstract

The Espinhaço Supergroup cropping out between the cities of Macaúbas and Canatiba, in the northernEspinhaço range, Bahia, is composed by the Pajeú Group (metarhythmites and intermediate to acidmetavolcanics), the Bom Retiro Formation (mature quartzites with metric to decametric cross-bedding), theSão Marcos Group (quartzites with wavy stratification and wave-related cross-bedding, intercalated with micaschists)and the Sítio Novo Group (cross-bedded, conglomeratic and massive quartzites, metarhythmites andmetapelites). The bedrock (gneisses and schists) is tectonically emplaced over the Espinhaço Supergroup inthe eastern portion of the area, and the Espinhaço Supergroup is unconformably covered by the Santo OnofreGroup (graphite-phyllites and metarhythmites) in the western portion of the area. This whole stratigraphicpackage is inverted, allowing, together with relations between bedding and schistosity, to define a largeinverted limb of an assymmetric fold with axis NNW-SSE.In the Veredas Formation, intermediate portion of the Sítio Novo Group, occurs a bed of approximately10 m of deep blue dumortierite-quartzites, used as ornamental rocks. Samples of these rocks have beenanalysed using optic, cathodoluminescence and electronic microscopic techniques, revealing its mineralogicand micromorphologic features.Comparing the stratigraphic and sedimentologic features of the studied area with other outcropping areas ofthe Espinhaço Supergroup, it can be concluded that it has evolved through three sedimentary megacycles,represented on each of the portions of the Espinhaço Range and Diamantina Plateau in the eastern regionof Brazil. The first megacycle involves syn-rift sedimentation, starting at about 1,75 Ga (Statherian Period).The second megacycle involves fundamentally eolian sedimentation. The third megacycle involves mainlyshallow marine to transitional sedimentation, with important tectonic reativation in the northern sector ofthe basin. All megacycles evolded in intracratonic environment..