Marcelo Juliano de Carvalho

Evolução do segmento norte do orógeno Itabuna-Salvador-Curaçá: cronologia da acresção de arcos, colisão continental e escape de terrenos

U-Pb and Pb-evaporation zircon ages, together with whole-rock Sm-Nd and Pb-Pb data, are used to unravel the tectonic evolution of the northern segment of the Itabuna-Salvador-Curaca Orogen, northeastern Sao Francisco Craton. The results of this geochronologic study indicate that oceanic crust and island arc sequences accreted at 3.3 Ga, forming the Mundo Novo Greenstone Belt, and that between 2.2 - 2.12 Ga the Rio Itapicuru and Rio Capim Greenstone Belts were formed in a similar fashion. Age data and Nd isotopes also suggest that Andean-type continental margins are likely to have formed in the span of time 3.08 - 2.98 Ga, giving rise to the TTG belts of Retirolândia and Jacurici river, and to the Caraiba Complex between 2.69 - 2.63 Ga. Around 2109 Ma, continent-continent collision closed the Rio Itapicuru volcano-sedimentary basin, as inferred from the syntectonic emplacement of the Itareru Tonalite between the Rio Itapicuru Greenstone Belt to the east and the banded gneisses of the Serrinha Block to the west. This collision culminated in a major shift from frontal or oblique convergence to orogen-parallel block-escape about 2084 Ma ago and continued at least till 2039 Ma. During this event several elongated granitic and syenitic bodies were emplaced in the continental crust. The Itiuba Syenite, dated at 2084 Ma and stretching over 150 km east of the Caraiba Complex, is an example of one of these intrusive bodies.

Estratigrafia e geocronologia do greenstone belt de Guarinos, Goiás

The Guarinos greenstone belt is one of the three low metamorphic grade supracrustal rocks assemblage rimmed by orthogneisses of Central Brazils Archean Block northern limits. The investigation of the stratigraphy of those greenstone belts started by the end of 1970s and underwent improvements during the years as a result of detailed geological mapping. The latest and accepted stratigraphic model for the Guarinos greenstone belt refers its supracrustal rocks under the Guarinos Group, which is subdivided into the Serra do Cotovelo (metakomatiites), Serra Azul (metabasalts), Sao Patricinho (mafic metaturbidites), Aimbe (BIF) and Cabacal (carbonaceous phyllites and impure metarenites) formations. Detailed geologic mapping (1:10,000) and drill-cores during an exploration program by Yamana Desenvolvimento Mineral S.A. in the area allowed a better definition of the metasedimentary package of the Cabacal Formation, which is here formally proposed to be subdivided into a Lower Member of carbonaceous phyllites with basalt lava flows and gondite lenses interlayers, an Intermediate Member of gondite, iron formation, metachert and massive barite lenses, and an Upper Member of carbonaceous phyllites with minor metachert lenses. The impure metarenites, formerly considered as part of the Cabacal Formation, are proposed under the Mata Preta Formation, which is laterally interfingered with the Cabacal Formation. U-Pb LA-ICP-MS geochronological data of detrital zircon grains from the Sao Patricinho mafic metaturbidites and the impure metarenites of the Mata Preta formations indicate that the major source-area of the clastic load had a Siderian to Rhyacian age, with minor contribution from Archean rocks. From the rock assemblage of both units and their contact relationships it is concluded that the basin stage they represent evolved during the world-wide Anoxic Oceanic Event (AOE) that took place during the 2.2 to 2.06 Ga, represented by the carbonaceous phyllites of the Cabacal Formation, coeval with the erosion of a magmatic arc that derived the immature clastic load of the Mata Preta Formation.

The Sergipano Belt

The Neoproterozoic Sergipano is the main orogenic belt between the Borborema province in the north and the Sao Francisco craton in the south. The belt is divisible from north to south into the Caninde, Poco Redondo-Maranco, Macurure, Vaza Barris, and Estância lithostratigraphic domains; the first three are composed of plutonic, volcanic and sedimentary rocks, and the last three of sedimentary rocks. Field relationships combined with zircon geochronology of igneous and sedimentary rocks and whole-rock elemental and isotopic data allow us to propose the following evolution for the Sergipano belt. An early Neoproterozoic (~980–960 Ma) continental arc (Poco Redondo tonalitic gneisses) developed on the margin of the Paleoproterozoic-Neoproterozoic Pernambuco-Alagoas block in the north. Extension of this continental block gave rise to: (i) A-type crustal melt granites and associated sedimentary rocks on the stretched, rifted margin of the Poco Redondo-Maranco domain; (ii) the Caninde rift sequence between the Pernambuco-Alagoas block and the Poco Redondo/Maranco domain; (iii) a passive margin on the southern boundary of the Pernambuco-Alagoas block, upon which sediments were deposited soon after 900 Ma; and (iv) a second sedimentary shelf on the passive margin of the Sao Francisco craton. In the Caninde domain, rifting continued until ca. 640 Ma and led to emplacement of a bimodal association of A-type granites (715 Ma) and continental mafic volcanic rocks, a continental-type layered gabbroic complex (ca. 700 Ma), magma-mingled gabbro/quartz–monzodiorite (688 Ma), and rapakivi granites (684 and 641 Ma). Deformed pillow basalts and interleaved marble lenses are likely ocean floor relicts in the Caninde domain. Closure of the Caninde oceanic basin began at ca. 630 Ma with the intrusion of arc-type granitic plutons in the Macurure (628–625 Ma), Caninde (ca. 621 Ma) and Poco Redondo-Maranco (ca. 625 Ma) domains. Convergence of the Pernambuco-Alagoas block and the Sao Francisco craton led to deformation on the passive margins and granite emplacement (590–570 Ma) mainly in the Macurure domain. Exhumation of the Pernambuco-Alagoas block and the Caninde, Poco Redondo-Maranco, and Macurure domains in the north led to deposition of uppermost clastic sediments in the Estância and Vaza Barris domains in the south, interpreted as a foreland basin, and to final thrusting of the continental margin sedimentary rocks onto the Sao Francisco craton.