Filling Materials in Brittle Structures as Indicator of Cenozoic Tectonic Events in Southeastern Brazil

The filling materials in brittle structures can provide useful information about the Cenozoic evolution developed over proterozoic terrains. When these materials are affected by faults, they record deformation phases that can be determined chronologically and, in the occurrence of lateritic materials, it is possible to infer the paleoenvironmental conditions during the mineral formation. This work aimed to identify crystalline phases of brittle structure filling materials and to propose evolutionary interpretations for Cenozoic tectonic reactivation based on literature data. The study area is located in the Southern part of the Espirito Santo State, near the Brazilian Southeastern Continental Margin, where proterozoic geological structures have been reactivated since the mesozoic rift phase, up to the Holocene. The mineral assemblage found in the filling materials includes primary minerals such as quartz, muscovite, microcline, rutile, titanite, and bannisterite; and the weathering minerals such as kaolinite, illite, hematite, goethite, hydrobiotite, lithiophorite and, birnessite. The mineralogical association found in the filling materials denotes the action of fluid phases with mineral precipitation at the brittle discontinuities during the weathering processes that occurred during the Cenozoic, probably between the Miocene and the Pleistocene. The faults, which striations are marked on the filling materials, originated after (in the case of the manganese oxides) or during (in the case of the illite) the mineral formation, indicating that the maximum age of these faults is in the Miocene. The origin of the brittle structures that affected the filling materials studied here is linked to the uplifting of the Continental Brazilian Margin, when ancient geological structures were reactivated asnormal faults due to the local action of an extensional regime.