Edison J. Milani

Basement control and transfer tectonics in the Recôncavo-Tucano- Jatobá rift, Northeast Brazil

Abstract The Reconcavo-Tucano-Jatoba rift consists of a series of asymmetric grabens which are separated by basement highs and transfer faults. Opening of the rift took place in a NW direction oblique to the N-S rift trend. Well defined transfer faults parallel the opening direction. They were responsible both for offsetting en-echelon depocenters in the Tucano and Reconcavo basins and for switching of the asymmetry of half-grabens across the Vaza-Barris fault zone. The transfer faults show characteristic features such as change of movement sense along strike and with time, and “cactus-shaped” fault structures as well as flower structures in cross section. The sigmoidal plan-form of the rift is probably due to faulting following pre-existing weaknesses through a complex mosaic of basement blocks. Basement anisotropy is thought to have controlled the asymmetry of the half-grabens and the localisation of the Vaza-Barris transfer. A 2° anticlockwise rigid rotation of the East Brazilian Microplate relative to the Sao Francisco Craton around a pole located near the eastern termination of the Jatoba Graben describes the calculated 20% extension in the South Tucano and Reconcavo grabens, the oblique northwestward opening, and the eastward shallowing of the Jatoba Graben. Gravity modelling suggests important crustal thinning, locally up to 45%, below the rift. Mantle upwarping is localized near the faulted margin of the rift. With localized thinning in a 100 km wide basin during a 20 Ma rifting event, lateral, as well as vertical heat conduction would be important and may account for the absence of a post-rift thermal subsidence phase.

Mesozoic and Cenozoic igneous activity and its tectonic control in northeastern Brazil

Abstract The northeastern region of the South American Platform corresponds to a peculiar Brazilian tectonic unit, the Borborema Province. It is a highly complex region due to its tectonic setting, as well as to extensive intrusive and extrusive igneous activity that took place during the Mesozoic and Cenozoic. A regional tectonic analysis based on the spatial and temporal distribution of geochronological data (K/Ar ages) led to the recognition of two main magmatic stages. The earlier events (Upper Jurassic to Lower Cretaceous) are related to the origin of several sedimentary rift basins in the area. The Tertiary alkaline magmatism presents a characteristic distribution whose linear trend suggest the track of an active hot spot in the region.

Correlations between the classic Paraná and Cape–Karoo sequences of South America and southern Africa and their basin infills flanking the Gondwanides: du Toit revisited

Abstract Early during the twentieth Century, pioneering correlations between the Palaeozoic–Mesozoic basins of South America and southern Africa were used by Alexander du Toit to support the initial concepts of continental drift and the proposal of a united Gondwana continent. New stratigraphic tools and data can now be used to further tease out similarities and differences to reconstruct the detailed histories of these, the Paraná and Cape–Karoo basins. In turn this knowledge can be used also to increase our understanding of the origin and evolution of Gondwana. Recent advances in tectonics and stratigraphy showed that both basins evolved together along a common early Palaeozoic Gondwana margin facing the Panthalassa. Thereafter, this margin was transformed into a series of linked foreland basins coupled to the evolution of the Gondwanides. In detail, the foreland successions differ considerably due to spatial and temporal differences in tectonic histories along the Gondwanides. Only towards the end of the Palaeozoic did both basins evolve and merge into a single continental-scale, and truly intracratonic, terrestrial Gondwana basin that persisted until the early Cretaceous. This shared history was once again disrupted in the Early Cretaceous during the opening of the South Atlantic Ocean.

Microplate rotation in northeast Brazil during South Atlantic rifting: Analogies with the Sinai microplate

The Early Cretaceous northeast Brazilian Sergipe microplate, formed at the northern end of the South Atlantic rift between South America and Africa, closely resembles the modern Sinai microplate at the northern end of the Red Sea in size, shape, and relative motion. Both formed where east-northeast–trending transverse shear zones arrested northward rift propagation, causing the Tucano-Reconcavo and Gulf of Suez rifts to fail and be replaced by northeast-trending leaky transforms (Sergipe-Alagoas and Dead Sea transforms) as the new paths of continental breakup. Bordered by the failed rift, the leaky transform, and the transverse shear zone, both microplates were rotated counterclockwise by drag along their eastern transform margins. Rotation thrust the edge of the Sergipe microplate over part of its northern border, creating the Arcoverde thrust wedge. The northwest-trending Vaza-Barris fault sheared the microplate, transferring the rift and evaporite sequence from the Sergipe-Alagoas to the Gabon continental margin. In Albian time, heating of the lithosphere in the Cabo igneous province near Recife permitted the South Atlantic rift to propagate across the Arcoverde thrust wedge, completing continental breakup.

Chapter 34 - Mesozoic rift basins around the northeast Brazilian microplate (Recôncavo – Tucano – Jatobá, Sergipe – Alagoas)

Abstract The northeast Brazilian microplate, a key element in the continental breakup between South America and Africa, was detached from both continents by the early Cretaceous rifting event. From Africa it became separated by the NE-trending, divergent, left-lateral Sergipe – Alagoas shear zone; from South America by the reactivation of the E – W trending, right-lateral Pernambuco shear zone and by the N – S trending Reconcavo – Tucano rift. The rifts and pull-apart basins bordering the microplate provide most of Brazils oil produced on land.

New Regional Correlations Between the Congo, Paraná and Cape-Karoo Basins of Southwest Gondwana

Pioneering stratigraphic correlations by J. Keidel and A. du Toit, in the first half of the twentieth century, first highlighted significant similarities between the age-rock sequences in southern Africa and eastern South America, supporting A. Wegener’s concept of a united Gondwana supercontinent. Based on subsequent field investigations and modern sedimentary basin analysis of the Congo Basin of central Africa and the Parana Basin of southeastern Brazil, we revisit these early correlations and derive new paleogeographic reconstructions of the interior of southwest Gondwana. Following late Neoproterozoic-Early Cambrian amalgamation of Gondwana, earliest Paleozoic continental red-bed sediments were deposited regionally southward across the peneplained Central African and Kalahari Shields. Thereafter, Ordovician-Devonian subsidence along a vast shallow marine platform bordering the southwestern margin of Gondwana linked the Parana Basin with the Cape-Karoo Basin of South Africa. Equivalent sequences are absent in the Congo Basin. In contrast, succeeding Carboniferous-Permian and Triassic successions are similar in all the Congo, Parana and Cape-Karoo Basins, including thick transgressive glacial and deglaciation sequences overlain by progressively terrestrial and arid sediments, which suggest a single Central West Gondwana Basin (CWGB) complex. This late Paleozoic-early Mesozoic cycle of subsidence of the CWGB can possibly be linked to long wavelength flexure of Gondwana continental lithosphere related to the Mauritanian-Variscan and Cape-de la Ventana orogens along the northwestern and southern margins of the supercontinent, around ca. 300 Ma and 250 Ma, respectively. Following Jurassic-Cretaceous hot and arid sedimentation across southwest Gondwana culminated in widespread deposition of northerly-derived aeolian dunes, episodically interrupted by successive eruption of Large Igneous Provinces during the initial phases of Gondwana break-up (ca. 183 Ma and 132 Ma). This shared sedimentation and climatic history of the Congo, Parana and Cape-Karoo Basins was then disrupted by the Early Cretaceous opening of the South Atlantic Ocean and the Kalahari epeirogeny, after which the Congo Basin survived and recorded intermittent phases of lacustrine and fluvial deposition.