TESES DE DOUTORADO EM GEOCIÊNCIAS SOBRE REGIÕES BRASILEIRAS
(DEFENDIDAS EM UNIVERSIDADES ESTRANGEIRAS)

Luiz José Homem D'el-Rey Silva
ldel-rey@unb.br

EVOLUÇÃO TECTÔNICA DA PARTE SUL DA FAIXA SERGIPANA, NORDESTE DO BRASIL

Ver Mapa Geológico

Palavras-chave: Faixa Sergipana; Brasil; Cráton São Francisco; Neoproterozóico; Sergipe e Bahia; Análise Estrutural; Análise Estratigráfica; Evolução Tectônica

Royal Holloway University London (RHUL)
Egham (Surrey) - England

DATA DE DEFESA: 02 /11 / 1992
ÁREA DE CONCENTRAÇÃO: Geologia Estrutural e Tectônica
ORIENTADOR: Prof. Kenneth Raymond McClay
EXAMINADORES: Prof. Michael Coward
Prof. John Grocott
Prof. Kenneth R. McClay

Luiz José Homem D'el-Rey Silva
ldel-rey@unb.br

TECTONIC EVOLUTION OF THE SOUTHERN PART OF THE SERGIPANO FOLD BELT, NORTHEASTERN BRAZIL

Geologic Map

Key words: Sergipano Fold Belt; Brazil; São Francisco Craton; Neoproterozoic; Sergie and Bahia States; Structural analysis; Stratigraphic analysis; Tectonic Evolution

Royal Holloway University London (RHUL)
Egham (Surrey) - England

DATE OF ORAL PRESENTATION: 02 /11 / 1992
TOPIC OF THE THESIS: Structural Geology and Tectonics
SUPERVISOR: Prof. Kenneth Raymond McClay
COMMITTEE MEMBERS: Prof. Michael Coward
Prof. John Grocott
Prof. Kenneth R. McClay

ABSTRACT
This thesis is a stratigraphic and structural analysis of the Itabaiana Dome area in the southern part of the Sergipano Fold Belt, northeastern Brazil. The ESE-WNW trending Sergipano Fold Belt is a subgreenschist to amphibolite grade metavolcano-sedimentary wedge polydeformed during the 700-600 Ma Brasiliano - Pan-African orogeny. Crystlline basement gneiss domes mantled by metasediments are found within the fold belt which lies between the São Francisco Craton in the south and the Pernambuco-Alagoas Massif to the north. An area of 4000km² surrounding the Itabaiana and Simão Dias gneiss domes was mapped at 1:50,000 scale.
A new stratigraphy has been established for this part of the Sergipano Fold Belt. Two major Middle to Late Proterozoic sedimentary cycles have been recognised, each with a basal siliciclastic megasequence overlain by a carbonate megasequence. Four main stratigraphic groups have been established. The ˜ 330m thick Estância Group consisting of metasandstones, pelites, and metacarbonates unconformably overlies the crystalline rocks of the craton and is laterally equivalent to the ˜200-1100m thick Miaba Group which consists of the Itabaiana quartzites; the Ribeirópolis phyllites, pebbly phyllites, diamictites and metavolcanics; and the Jacoca metacarbonates. The Miaba Group is unconformably deposited around the gneiss domes. The ˜700m thick Lagarto Group has been identified as a new lithotectonic element in the southern part of the Sergipano Fold Belt. This Group is a coarsening-upward siliciclastic sequence that overlies the older rocks of both the craton and the fold belt. It consists of the Lagarto-Palmares mudstones, siltstones, sandstones and lithic wakes together with the Jacaré metasiltites and the Frei Paulo phyllites, metarhythmites, metagreywackes, minor metacarbonates and metavolcanics. The ˜200-2000m thick Vaza Barris Group, consisisting of the Palestina diamictites and the Olhos D’água metacarbonates, unconformably overlies the older rocks to the north of the Itaporanga fault.
The thickest Palestina diamictites occur in a WNW-ESE trending, fault-bounded depocentre which also received relatively deep water accummulations of the other formations. The siliciclastics generally thin towards the basement gneiss domes, whereas the carbonates thin away from the domes into the diamictite trough. The thickness and facies distributions of these units indicate tectonically controlled sedimentation, with basement highs supplying sediments from both the southern and northern margins of an asymmetric basin.
The structure of the Itabaiana Dome area is dominated by shallowly plunging, SSW vergent F₁ and F₂ recumbent to inclined folds and steep D₂ thrust faults. D₁ is characterised by WNW-ESE trending, SW vergent, nappe-like folds associated with a penetrative layer-parallel foliation. D₂ is characterised by co-axial, up-right, tight and WNW-ESE trending folds, associated with penetrative axial surface foliations, lineations and high-angle, SSW vergent, oblique slip thrust faults. These regional thrust faults are probably inverted extensional faults. Late-stage, orogen-parallel movement generated transverse F₃ kink-style folding and rotation of fault bounded domains.
Regional lithostructural correlations between the southern and northern parts of the Sergipano Fold Belt indicate that the Sergipano Basin may be interpreted to have been a WNW-ESE striking half graben that deepened towards the ENE. It was infilled by miogeoclinal-eugeoclinal sediments and evolved axially into a small oceanic basin, termed the Canindé sea, in its northern part. The preferred tectonic model for the evolution of the Sergipano Basin is that of a linked system of listric extensional faults that merged into a basal detachment with a ramp-flat geometry. Inversion of this extensional fault system, due to oblique collision of the Borborema Province to the north, with the São Francisco Craton to the south, produced sinistral transpression of the sedimentary wedge of the Sergipano Basin and resulted in the Sergipano Fold Belt.
The tectonic and stratigraphic evolution of the Sergipano Fold Belt is similar to that found in other Brasiliano and pan-africa mobile belts. In particular the correlation of stratigraphy from the craton into the fold belt and the interpretation of sedimentation controlled by extensional tectonics suggest a model of basin formation by extension of the craton margins, development of pericratonic and small oceanic basins which were then deformed by collision of continental fragments against the craton margins. This model agrees with those postulated of a supercontinent that evolved by fragmentation and amalgamation of along long-lived zones of lithosphere weakness throughout the Proterozoic.