Piancó-Alto Brígida branching system of orogens (PE-PB-CE), Tectonic regionalization and geochronology

O Sistema de Dobramentos Piancó-Alto Brígida (SPAB) situa-se na porção central a centro-ocidental da Zona Transversal, da Província Borborema, nos Estados da Paraíba e do Pernambuco e em parte do Estado do Ceará. Trata-se do produto de um desenvolvimento orogenético na passagem Criogeniano-Ediacarano (630–580 Ma, acresção seguida de colisão), levando à inversão vigorosa de uma pretérita bacia de sedimentação marinha costeira. O limite ao norte é marcado pelo Lineamento de Patos e o ao sul é balizado pelo Lineamento Pernambuco. O contexto paleogeográfico (e litoestratigráfico) original é de reconstituição difícil devido aos eventos de deformação (pelo menos três fases) e metamorfismo, lateralmente variável de muito baixo, baixo a médio graus, seguidos de uma importante fase de tectônica extrusional tardia. O SPAB se encontra hoje geológico-geograficamente ramificado em diferentes faixas, separadas por alguns basement inliers, paleoproterozoicos/“terrenos”, expressivos em área e importantes partícipes dos eventos de deformação. Os principais litotipos presentes no SPAB se enquadram nas típicas assembleias quartzito-pelito-calcário (QPC) com a característica primordial da grande ritmicidade. Os gradientes metamórficos são de muito baixo, baixo e médio graus (nesse último caso, para o sul, faixa do interior de Pernambuco, “Supergrupo Salgueiro”). Nas zonas proximais dos contatos com o embasamento, consoante a linhas de falhas importantes, são registrados brechas e conglomerados polimícticos, arenitos imaturos, metagrauvacas e metacórseos (Formação Olhos d’Água). Embora haja várias contribuições, de diversas fontes, ao longo dos últimos 50 anos, em diferentes tempos e propósitos, uma discriminação da litoestratigráfica satisfatória ainda não foi possível. De sorte que todos os termos litoestratigráficos devem ser encarados como informais e provisórios. Múltiplos trabalhos de reconhecimento em geocronologia foram realizados aleatoriamente nesse sistema nas The Piancó-Alto Brígida branching system of orogens (SPAB) is in the central and center-western part of the Transversal Zone, of Borborema Province, in the states of Paraíba, Pernambuco and Ceará. It is a final tectonic product of an orogenetic development during Cryogenian-Ediacarian periods. The original paleogeographic (and lithostratigraphic) scenery is of difficult reconstitution due to tectonic events (at least three different phases of folding), with lateral variations of the metamorphism’s degree from very low to low grade. These events were followed by an important final phase of escape tectonics (extrusion). Today, the SPAB is geographically branched into different fold belts, bounded by some Paleoproterozoic basement inliers that are expressive both in area and participation in the regional deformation. The main lithological assemblages present in the SPAB belts may be classified as part of typical QPC (quartzite-pelite-carbonate) assemblages, with a striking characteristic of remarkable rhythmicity, as well as the metamorphic gradient very low to low grades up to medium grade (to the belt of the interior of Pernambuco “Supergurpo Salgueiro”). Along the zones near the contacts with the basement (following important fault lines) polymictic breccias and conglomerates, immature sandstones and arkoses (“Formação Olhos d´Água”) are recorded. Even though there are many sources of scientific contributions on this subject in the last 50 years, at different times and purposes, a satisfactory lithostratigraphic classification was not possible. So all the lithostratigraphic terminology (here discussed) should be faced as informal and provisory. Many reconnaissance projects of geochronology have been done along the two last decades. In the last years, a systematic program of geochronological research (Sm-Nd and U-Pb methods) has been developed trying to&nbsp

A zona tectônica Teixeira Terra Nova - ZTTTN: fundamentos da geologia regional e isotópica

A sigmoidal-shape linear tectonic zone occurs from Teixeira (Paraíba, to the north-northeast)- to Terra Nova (Pernambuco, to the south-southwest) as a line diagonal to the"Transversal Zone", which is the central tectonic portion of the Borborema Province, thus dividing this province into two different litho-structural and tectonic domains. To the north and northwest occur the Early Neoproterozoic Riacho Gravatá (RG) and the Neoproterozoic Piancó-Alto Brígida (PAB) terranes, both of them characterized by supracrustal rocks with low-grade of regional metamorphism. To the south-southwest occur the Alto Pajeú terrane (TAP, Early Neoproterozoic, orthognaisses and mesozonal supracrustal rocks) and the domain of its basement, the Alto Moxotó terrane (TAM, Paleoproterozoic in age), with high grade metamorphic rocks. This proposed"tectonic zone" is mostly composed by orthogneisses (from TAP and its Paleoproterozoic basement) pierced by an almost continuous series of intrusive granitic and syenitic rocks (plutons and stocks) of the Ediacaran period (ages between 630 and 570 Ma). During the evolutionary history of this linear portion of the plateau of the Borborema province there are some (direct and indirect) records of polycyclic geologic events of the Paleoproterozoic, Early Neoproterozoic, Ediacaran, Cambrian and Cenozoic era (a sedimentary veneer, evolution of a supergenic crust and regional uplift) with interesting implications for the regional geology, geography and social-economic development. In this paper the emphasis will be given to the isotopic data (Rb-Sr, Sm-Nd, mostly) along this special zone and the domains that it separates, as well its role on the regional tectonic framework. For this purpose, we take into consideration an expressive amount of available geological and isotopic data, obtained along the last decade (most of them not published) from different sources. Additionally, some first interpretative hypotheses will be postulated, where this tectonic zone (ZTTTN) would be formed as by-product of three parallel Neoproterozoic subduction zones.Uma zona tectônica linear, de forma sigmoidal, ocorre de Teixeira (Paraíba, ao norte-nordeste) a Terra Nova (Pernambuco, ao sul-sudoeste), com disposição diagonal ao domínio da Zona Transversal - ZT, que é a porção central da Província Borborema, de forma a subdividir a ZT em dois domínios lito-estruturais e geotectônicos distintos. Para norte e noroeste ficam os terrenos do Riacho Gravatá - RG (Eoneoproterozóico) e Piancó-Alto Brígida - PAB (Neoproterozóico), caracterizados por baixo grau de metamorfismo. Para o sul e sudeste fica o terreno Alto Pajeú (TAP, Eoneoproterozóico, ortognaisses e rochas supracrustais mesozonais) e seu embasamento, terreno Alto Moxotó - TAM (Paleoproterozóico), de grau médio a elevado de metamorfismo. Esta zona linear ou"alto" constituído de ortognaisses (do TAP e do embasamento paleoproterozóico que aflora esparsamente) é perlongado e marcado por uma série quase contínua de rochas intrusivas, plutões e stocks graníticos variados e sieníticos do tempo Ediacarano (idades entre 630 e 570 Ma, principalmente). Na história evolutiva desta porção linear particularmente soerguida do Planalto da Borborema há o registro (direto e/ou indireto) de eventos geológicos policíclicos, do Paleoproterozóico, do Eoneoproterozóico, do Ediacarano, do Eocambriano e do Cenozóico (sedimentação correlativa, elaboração de crostas e soerguimento regional), com implicações interessantes na geografia e sócio-economia regional. No presente trabalho será dada ênfase aos dados isotópicos (métodos Rb-Sr, Sm-Nd sobretudo) desta zona diferenciada, e nos contextos por ela separados, assim como no seu papel dentro do contexto tectônico regional, usufruindo para isto de expressivo acervo de dados geológicos e isotópicos, obtidos na última década (grande parte do qual ainda inédita). Além disso, hipóteses interpretativas serão postuladas para esta linha axial tectônica que subdivide a Zona Transversal em domínios geológicos distintos, considerando-a como conseqüência e subproduto de três processos paralelos de subducção no Neoproterozóico

Contribution to the knowledge of the geological evolution of the Riacho do Pontal orogenic system – PE, BA, PI

O Sistema Riacho do Pontal (SRP) é a parte central de um desenvolvimento orogênico neoproterozoico na periferia norte do Cráton do São Francisco (CSF), de nordeste (Faixa Sergipana) para noroeste (Faixa Rio Preto). O embasamento do antepaís (CSF) e do além-país (Morro do Estreito-Icaiçara) são constituídos em parte por rochas arqueanas, e desse terreno para a zona interna há registros de supracrustais e ortognaisses do Toniano (Ciclo Cariris Velhos?). O SRP apresenta notório zoneamento de norte para sul: além-país; zona interna (litotipos terrígenos); zona central (marcadas por rochas do assoalho oceânico); zona externa (litotipos terrígenos) e o domínio cratônico (CSF), com a presença de largo (> 200 km) foreland thrust and fold belt, mais para o sul, formado pela cobertura pelítico-carbonática do CSF. A deformação é intensa e apresenta vergência voltada para sul e sudeste, com dobras recumbentes e deitadas, falhas inversas e de empurrão, nappes e particularmente o registro de algumas klippen sobre o embasamento do CSF. O metamorfismo regional é geralmente na fácies anfibolito, com retrogressões locais a fácies xisto verde. Este trabalho apresenta uma série de determinações geocronológicas (métodos Rb-Sr, Sm-Nd e U-Pb) de praticamente todos os litotipos de embasamento, das supracrustais e dos granitos sincolisionais associados. Foram discriminados um substrato arqueano (além-país, idades neoarqueanas entre 2740 – 2624 Ma) e duas faixas meta-vulcanossedimentares com granitoides inseridos do Neoproterozoico, uma do Eotoniano (980 – 940 Ma) e outra do limite Criogeniano -Ediacarano (ca. 635 Ma). Um ensaio preliminar da evolução geotectônica do SRP é esboçado em termos “wilsonianos” para essa porção mais sul-ocidental da Província Borborema, atribuída a um sistema regional ramificado de orógenos.The Riacho do Pontal System (RPS) is just the central part of a long Neoproterozoic orogenic development placed at the northern periphery of the São Francisco Craton (SFC), from northeast (Sergipano belt) to southwest (Rio Preto belt). The basement of the foreland (SFC) and the backland (“Morro do Estreito-Icaiçara”) is mostly formed by Archean rocks, with some insertions of supracrustal and orthogneisses of Tonian age (Cariris Velhos cycle?). RPS exhibits a remarkable tectonic-metamorphic zoning from north to the south: the backland; the internal zone (supracrustal terrigenous assemblages); the central zone (ocean floor rock assemblages); the external zone (supracrustal terrigenous assemblages); and the cratonic domain (SFC), remarked by the presence of a wide (> 200 km) foreland thrust and fold belt (to the south), formed by the Neoproterozoic pelitic-carbonatic cratonic cover. The processes of deformation were intense, presenting vergence towards south and southwest, resulting in reclined and overturned folds, reverse and thrust faults, nappes, and specially the occurrences of some klippen over the basement of the northern part of the CSF. The regional metamorphism was undertaken under amphibolite conditions, with some local retrogression to the greenschists facies. This paper presents a series of new geochronological determinations (Rb-Sr, Sm- Nd and U-Pb methods) of practically all rock types of the basement, supracrustals, and of the associated syncollisional granites. It was possible to discriminate some Archean nuclei (2740 – 2624 Ma), as basement (backland), and two different set of Neoproterozoic volcano-sedimentary rock units associated with granites, the first one of Eotonian age (980 – 940 Ma) and the second one positioned in the Cryogenian-Ediacaran boundary (ca. 635 Ma). A preliminary essay of “wilsonian” tectonic evolution is here introduced for this south-western portion of the Borborema Province (the regional branching system of orogens)

The Cariris Velhos tectonic event in Northeast Brazil

The Borborema Province in northeastern South America is a typical Brasiliano-Pan-African branching system of Neoproterozoic orogens that forms part of the Western Gondwana assembly. The province is positioned between the Sao Luis-West Africa craton to the north and the Sao Francisco (Congo-Kasai) craton to the south. For this province the main characteristics are (a) its subdivision into five major tectonic domains, bounded mostly by long shear zones, as follows: Medio Coreau, Ceara Central, Rio Grande do Norte, Transversal, and Southern; (b) the alternation of supracrustal belts with reworked basement inliers (Archean nuclei + Paleoproterozoic belts); and (c) the diversity of granitic plutonism, from Neoproterozoic to Early Cambrian ages, that affect supracrustal rocks as well as basement inliers. Recently, orogenic rock assemblages of early Tonian (1000-920 Ma) orogenic evolution have been recognized, which are restricted to the Transversal and Southern domains of the Province. Within the Transversal Zone, the Alto Pajeu terrane locally includes some remnants of oceanic crust along with island arc and continental arc rock assemblages, but the dominant supracrustal rocks are mature and immature pelitic metasedimentary and metavolcaniclastic rocks. Contiguous and parallel to the Alto Pajeu terrane, the Riacho Gravata subterrane consists mainly of low-grade metamorphic successions of metarhythmites, some of which are clearly turbiditic in origin, metaconglomerates, and sporadic marbles, along with interbedded metarhyolitic and metadacitic volcanic or metavolcaniclastic rocks. Both terrane and subterrane are cut by syn-contractional intrusive sheets of dominantly peraluminous high-K calc-alkaline, granititic to granodioritic metaplutonic rocks. The geochemical patterns of both supracrustal and intrusive rocks show similarities with associations of mature continental arc volcano-sedimentary sequences, but some subordinate intra-plate characteristics are also found. In both the Alto Pajeu and Riacho Gravata terranes, TIMS and SHRIMP U-Pb isotopic data from zircons from both metavolcanic and metaplutonic rocks yield ages between 1.0 and 0.92 Ga, which define the time span for an event of orogenic character, the Cariris Velhos event. Less extensive occurrences of rocks of Cariris Velhos age are recognized mainly in the southernmost domains of the Province, as for example in the Polo Redondo-Maranco terrane, where arc-affinity migmatite-granitic and meta-volcano-sedimentary rocks show U-Pb ages (SHRIMP data) around 0.98-0.97 Ga. For all these domains, Sm-Nd data exhibit Tom model ages between 1.9 and 1.1 Ga with corresponding slightly negative to slightly positive epsilon(Nd)(t) values. These domains, along with the Borborema Province as a whole, were significantly affected by tectonic and magmatic events of the Brasiliano Cycle (0.7-0.5 Ga), so that it is possible that there are some other early Tonian rock assemblages which were completely masked and hidden by these later Brasiliano events. Cariris Velhos processes are younger than the majority of orogenic systems at the end of Mesoproterozoic Era and beginning of Neoproterozoic throughout the world, e.g. Irumide belt, Kibaride belt and Namaqua-Natal belt, and considerably younger than those of the youngest orogenic process (Ottawan) in the Grenvillian System. Therefore, they were probably not associated with the proposed assembly of Rodinia. We suggest, instead, that Cariris Velhos magmatism and tectonism could have been related to a continental margin magmatic arc, with possible back-arc associations, and that this margin may have been a short-lived (<100 m.y.) leading edge of the newly assembled Rodinia supercontinent. (C) 2009 Elsevier Ltd. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)CNPq (Conselho Nacional de Pesquisas)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)U.S. National Science Foundation (NSF) to Van SchmusU.S. National Science Foundation (NSF) to Van Schmu

The tectonic significance of the Cabo Frio Tectonic Domain in the SE Brazilian margin: a Paleoproterozoic through Cretaceous saga of a reworked continental margin

ABSTRACT: The Cabo Frio Tectonic Domain is composed of a Paleoproterozoic basement tectonically interleaved with Neoproterozoic supracrustal rocks (Buzios-Palmital successions). It is in contact with the Neoproterozoic-Cambrian Ribeira Orogen along the SE Brazilian coast. The basement was part of at least three continental margins: (a) 1.97 Ga; (b) 0.59 - 0.53 Ga; (c) 0.14 Ga to today. It consists of continental magmatic arc rocks of 1.99 to 1.94 Ga. Zircon cores show a 2.5 - 2.6 Ga inheritance from the ancient margin of the Congo Craton. During the Ediacaran, this domain was thinned and intruded by tholeiitic mafic dykes during the development of an oceanic basin at ca. 0.59 Ma. After the tectonic inversion, these basin deposits reached high P-T metamorphic conditions, by subduction of the oceanic lithosphere, and were later exhumed as nappes over the basement. The Cabo Frio Tectonic Domain collided with the arc domain of the Ribeira Orogen at ca. 0.54 Ga. It is not an exotic block, but the eastern transition between this orogen and the Congo Craton. Almost 400 m.y. later, the South Atlantic rift zone followed roughly this suture, not coincidently. It shows how the Cabo Frio Tectonic Domain was reactivated as a continental margin in successive extensional and convergent events through geological time