Deformation bands and associated structures in the Tucano Basin, NE Brazil: A multiscale analysis

摘要

The sandstones of the Ilhas Group in the Tucano Basin (NE Brazil), are affected by numerous swarms of deformation bands (Dbs) and associated faults, developed in different deformation events (pre, syn and post stages of sediment lithification). We select an area located west of the city of Jeremoabo and east of the Agua Branca district, along the Vaza Barris River, for a multiscale structural analysis of these structures. NE-SW striking faults and swarms of Dbs are the main structures of the region but two other sets also occur, with NNW-SSE and E-W orientations. The structural analysis revealed that they are related to three deformational events, D-1 , D-2 and D-3. The D-1 event generated NE-SW normal faults and a combined system of transcurrent faults and dextral (NNWSSE) and sinistral (NE-SW) Dbs, developed under pre-to syn-lithification conditions of the sandstones. The D-2 event developed NNE-SSW oblique normal faults nucleated under post-lithification conditions. A younger deformational event (D-3) was responsible for the generation of NE-SW dextral and oblique normal faults both with associated Dbs swarm, A few NE-SW reverse and oblique reverse faults occur in the area. Tensional NW-SE and NNW-SSE stress fields associated with D-1 and D-2 events respectively, acted in the region during the Neocomian, while the D-3 event represents the NNE-SSW extension analogous to that responsible for the formation of the Brazilian Equatorial Margin during the Early Aptian.