scholarly journals Decratonization by rifting enables orogenic reworking and transcurrent dispersal of old terranes in NE Brazil

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Carlos E. Ganade ◽  
Roberto F. Weinberg ◽  
Fabricio A. Caxito ◽  
Leonardo B. L. Lopes ◽  
Lucas R. Tesser ◽  
...  
Keyword(s):  
Shear Zones ◽  
Boundary Region ◽  
The North ◽  
Pan African ◽  
Juvenile Material ◽  
Oceanic Basin ◽  
Borborema Province ◽  
Isotopic Model ◽  
Late Neoproterozoic

AbstractDispersion and deformation of cratonic fragments within orogens require weakening of the craton margins in a process of decratonization. The orogenic Borborema Province, in NE Brazil, is one of several Brasiliano/Pan-African late Neoproterozoic orogens that led to the amalgamation of Gondwana. A common feature of these orogens is that a period of extension and opening of narrow oceans preceded inversion and collision. For the case of the Borborema Province, the São Francisco Craton was pulled away from its other half, the Benino-Nigerian Shield, during an intermittent extension event between 1.0–0.92 and 0.9–0.82 Ga. This was followed by inversion of an embryonic and confined oceanic basin at ca. 0.60 Ga and transpressional orogeny from ca. 0.59 Ga onwards. Here we investigate the boundary region between the north São Francisco Craton and the Borborema Province and demonstrate how cratonic blocks became physically involved in the orogeny. We combine these results with a wide compilation of U–Pb and Nd-isotopic model ages to show that the Borborema Province consists of up to 65% of strongly sheared ancient rocks affiliated with the São Francisco/Benino-Nigerian Craton, separated by major transcurrent shear zones, with only ≈ 15% addition of juvenile material during the Neoproterozoic orogeny. This evolution is repeated across a number of Brasiliano/Pan-African orogens, with significant local variations, and indicate that extension weakened cratonic regions in a process of decratonization that prepared them for involvement in the orogenies, that led to the amalgamation of Gondwana.

scholarly journals Decratonization by Rifting followed by Orogeny and Transcurrent Dispersal of Old Terranes in NE Brazil: A Common Feature of Gondwana Amalgamation?

2020 ◽  
Author(s):  
Carlos Ganade ◽  
Roberto Weinberg ◽  
Fabricio Caxito ◽  
Leonardo Lopes ◽  
Lucas Tesser ◽  
...  
Keyword(s):  
Shear Zones ◽  
Boundary Region ◽  
The North ◽  
Juvenile Material ◽  
Borborema Province ◽  
Isotopic Model ◽  
Late Neoproterozoic

Abstract Dispersion and deformation of cratonic fragments within orogens in the periphery of cratons require weakening of the craton margins in a process of decratonization. The Borborema orogenic province, in NE Brazil, is one of several Brasiliano/Panafrican late Neoproterozoic orogens that led to the amalgamation of Gondwana. A common feature of these orogens is that a period of extension and opening of narrow oceans preceded inversion and collision. For the case of the Borborema Province, the São Francisco Craton was pulled away from its other half, the Benino-Nigerian Shield, during an extension event lasting between 1 Ga and 0.65 Ma. This was followed by inversion and a transpressional orogeny from c. 0.60 Ga onwards. Here we investigate the boundary region between the north São Francisco Craton and the Borborema Province and demonstrate how cratonic blocks became physically involved in the orogeny. We combine these results with a wide compilation of U-Pb and Nd-isotopic model ages to show that the BP consists of up to 65% of strongly sheared ancient rocks affiliated with the Sao Francisco/Benino-Nigerian Craton, separated by major transcurrent shear zones, with only ~ 15 % addition of juvenile material during the orogeny. This evolution is repeated across a number of Brasiliano/Panafrican orogens, with significant local variations, and indicate that extension weakened entire cratonic regions in a process of decratonization that prepared them for involvement in the orogenies that led to the amalgamation of Gondwana.

Basement inheritance affecting initiation and evolution of intracontinental rifts: Araripe Basin, northeast Brazil

2020 ◽  
Author(s):  
Pamela Richetti ◽  
Renata da Silva Schmitt ◽  
Bruno César Araújo ◽  
Maria Filipa da Gama ◽  
Marta Teixeira da Costa Soares
Keyword(s):  
Seismic Data ◽  
Shear Zones ◽  
Integrated Analysis ◽  
Rift System ◽  
Duplex System ◽  
Fault Systems ◽  
The North ◽  
Tectonic Events ◽  
Borborema Province ◽  
Formation And Evolution

<p>The structural inheritance of the basement plays an important role controlling rift formation and evolution. Here we investigate tectonic and rheological inheritance on brittle reactivation of the Precambrian basement and shear zones in the formation and evolution of the Cretaceous Araripe Basin. The basin is a part of the Northeast Brazilian Rift System, associated with the junction of the Southern and Equatorial branches of the Atlantic Rift. Its basement is part of Neoproterozoic Transversal Zone (Borborema Province), a crustal scale transpressional duplex system, related to the Brasiliano escape tectonic events. </p><p>We present here a synthesis of field observations from the Araripe Basin and its adjacent basement, combined with topographic, aeromagnetic and seismic data to propose a general overview on the tectonic framework and evaluate how it influenced the basin initiation and evolution. Our integrated analysis shows that there are three main structural trends for the basin and its surroundings: NE-SW, E-W and NW-SE. The NE-SW and E-W trends are the most expressive sets of lineaments in the topographic and aeromagnetic data, directly related to the basement framework. Integration of seismic data and filtered aeromagnetic maps confirms that NE-SW and E-W trends represent oblique fault systems.</p><p>Archean, Paleoproterozoic, Mesoproterozoic and Neoproterozoic terranes are arranged side by side in NE-SW mega sigmoid, bounded by the E-W Pernambuco (to the south) and Patos (to the north) dextral shear zones. The Araripe basin units are distributed mostly in two sub-basins, Cariri and Feira Nova, separated by a structural high, controlled by NE-SW and ESE-WNW faults. Analyzing these terranes and their link to the distribution of the depocenters and structures, we find that the NE trending Archean terrane coincides partially with the Feira Nova NE-SW single graben. On the eastern portion of the basin, the graben system is much wider and controlled by NE-SW and ESE-WNW trending fault systems. This wide graben overlies a Neoproterozoic basement terrane constituted by a supracrustal unit (Cachoeirinha Group) of phyllites, metasandstones, metavolcanics with low to medium metamorphic grade.</p><p>This evidence corroborates with the hypothesis that the rheology of the upper crust might be partially influenced by distinct lithotectonic terranes. The older Archean block sustained the narrow sub-basin, indicating a more localizing behavior, while the younger Neoproterozoic terrane, controlled a less localizing graben system with a wider sub-basin in the eastern Araripe basin.</p><p> </p><p>The authors gratefully acknowledge support from Shell Brasil Petroleo Ltda. and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation (Technical Cooperation #20.219-2).</p>

scholarly journals Pan-African extension and near-isothermal exhumation of a granulite facies terrain, Dronning Maud Land, Antarctica

2004 ◽  
Vol 141 (6) ◽  
pp. 649-660 ◽  
Author(s):  
A. K. ENGVIK ◽  
S. ELVEVOLD
Keyword(s):  
Shear Bands ◽  
Shear Zones ◽  
Granulite Facies ◽  
Magmatic Fluid ◽  
Pan African ◽  
Dronning Maud Land ◽  
Isothermal Decompression ◽  
Late Neoproterozoic ◽  
Tectonic Exhumation ◽  
Later Phase

The Mühlig-Hofmann- and Filchnerfjella in central Dronning Maud Land, Antarctica, consist of series of granitoid igneous rocks emplaced in granulite and upper amphibolite facies metamorphic rocks. The area has experienced high-temperature metamorphism followed by near-isothermal decompression, partial crustal melting, voluminous magmatism and extensional exhumation during the later phase of the late Neoproterozoic to Cambrian Pan-African event. Remnants of kyanite–garnet–ferritschermakite–rutile assemblages indicate an early higher-pressure metamorphism and crustal overthickening. The gneisses experienced peak granulite facies temperatures of 800–900 °C at intermediate pressures. Breakdown of garnet + sillimanite + spinel-bearing assemblages to cordierite shows subsequent re-equilibration to lower pressures. An E–W foliation dominating the gneisses illustrates transposition of migmatites and leucocratic melts which evolved during the near-isothermal decompression. Occurrence of extensional shear bands and shear zones evolving from the ductile partial melting stage through semiductile towards brittle conditions, shows that the uplift persisted towards brittle crustal conditions under tectonic W/SW-vergent extension. Late-orogenic Pan-African quartz syenites intruded after formation of the main gneiss fabric contain narrow semiductile to brittle shear zones, illustrating that the extensional exhumation continued also after their emplacement. The latest record of the Pan-African event is late-magmatic fluid infiltration around 350–400 °C and 2 kbar. At this stage the Pan-African crust had undergone 15–20 km exhumation from the peak granulite facies conditions. We conclude that the later phase of the Pan-African event in central Dronning Maud Land is characterized by a near-isothermal decompression P–T path and extensional structures indicating tectonic exhumation, which is most likely related to a late-orogenic collapsing phase of the Pan-African orogen.

scholarly journals Development of Crustal-Scale Shear Zones at the Singhbhum Craton–Eastern Ghats Belt Boundary Region: A Critical Review of the Mesoarchean–Neoproterozoic Odyssey

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 6) ◽  
Author(s):  
Gautam Ghosh ◽  
Proloy Ganguly ◽  
Shuvankar Karmakar ◽  
Sankar Bose ◽  
Joydip Mukhopadhyay ◽  
...  
Keyword(s):  
Shear Zones ◽  
Boundary Region ◽  
Eastern Ghats ◽  
Fault System ◽  
Tectonic Activity ◽  
Eastern Ghats Belt ◽  
Singhbhum Craton ◽  
The North ◽  
Suprasubduction Zone ◽  
Scale Shear

Abstract A number of crustal-scale shear zones have developed along the southern margin of the Singhbhum Craton, in the boundary with the Neoarchean Rengali Province and the Meso-Neoproterozoic Eastern Ghats Belt. The cratonic part, evolved in a suprasubduction zone setting, bears imprints of late Mesoarchean orogenic episode (D1C) at ca. 3.1 Ga with folding and thrust imbrication of the cratonic rocks. The succeeding orogenic imprint is etched in the Neoarchean (~2.8 Ga) with development of the Sukinda thrust along the craton margin and thrust-related deformation of the rocks of the Rengali Province (D2C-D1R). The latter event remobilized cratonic fringe with development of a spectacular E-W trending transpressional belt in the Southern Iron Ore Group rocks cored by the Sukinda ultramafics. In the Eastern Ghats Belt, the major ultrahigh-temperature orogeny took place during the Grenvillian-age (~1.0-0.9 Ga) assembly of the supercontinent Rodinia. This belt eventually got juxtaposed against the expanded Singhbhum Craton in the end-Neoproterozoic time (~0.5 Ga) along the Kerajang Fault Zone. This latter event remobilized a large part of the Rengali Province (D2R) with development of an intraterrane transpressional belt bounded by the Barkot Shear Zone in the north. The northern fringe of the intruding Eastern Ghats Belt developed a complex network of strike-slip fault system under this impact, probably an outcome of tectonic activity along the Kuunga suture, which signifies the joining of greater India with East Antarctica. The present synthesis visualizes early development in the craton through formation of a typical orogenic sequence, imbricated in thrust piles, resulting from a ca. 3.1 Ga orogeny. Further cratonic expansion was achieved via repetitive accretion and remobilization, development of crustal-scale faults and transpressional belts at ca. 2.8 Ga and ca. 0.5 Ga, much in a similar fashion as documented along oblique convergent margins of all ages.

scholarly journals ANÁLISE TECTÔNICA DA PORÇÃO NORDESTE DA FAIXA SERGIPANA, PROVÍNCIA BORBOREMA: DUPLA VERGÊNCIA EM RESPOSTA A COLISÃO OBLÍQUA ENTRE O CRÁTON DO SÃO FRANCISCO E O TERRENO PERNAMBUCO-ALAGOAS

2018 ◽  
Author(s):  
Haroldo Monteiro Lima ◽  
Márcio Martins Pimentel ◽  
Lauro Cezar Montefalco de Lira Santos ◽  
Vanildo Almeida Mendes
Keyword(s):  
Geometric Analysis ◽  
Shear Zones ◽  
Strain Partitioning ◽  
Fold Belt ◽  
Oblique Collision ◽  
Borborema Province ◽  
Thrust Tectonics ◽  
Late Neoproterozoic ◽  
Orogenic Belts ◽  
Belo Monte

Estruturas de dupla vergência são reconhecidas em cinturões orogênicos pré-cambrianos e fanerozoicos em resposta à partição da deformação entre componentes contracionais e transcorrentes em zonas transpressionais. A Faixa Sergipana é um importante segmento crustal localizado no sul da Província Borborema, NE do Brasil. Análise cinemática e geométrica em escala meso e microscópica realizadas na porção Nordeste da Faixa Sergipana revelou a existência de quatro fases deformacionais: Dn, D1, D2 e D3 que resultaram em inversão de transporte tectônico e imbricamento de complexos metavulcanossedimentares abundantes na região. O Domo Jirau do Ponciano representa o embasamento gnáissico migmatítico que preserva a trama mais antiga Dn. As fases posteriores (D1 e D2) representam tectônica contracional manifestada pelas zonas de cisalhamento de Jacaré dos Homens, Belo Monte-Jeremoabo e Palmeira dos Índios, e transcorrente/transpressional, respectivamente. Todo esse conjunto foi deformado por último por um episódio rúptil-dúctil (D3) responsável pela formação de fraturas, falhas e brechas de falhas. A combinação de dados estruturais e análise litoestratigráfica sugere que este arcabouço deve ter se desenvolvido em episódios contracionais distintos e retrabalhado durante o final do Neoproterozoico em resposta à colisão oblíqua entre o Terreno Pernambuco-Alagoas e o Cráton do São Francisco.Palavras Chave: Cinturões orogênicos, dupla vergência, Faixa SergipanaAbstract:TECTONIC ANALYSIS OF THE NORTHEAST SERGIPANA BELT, BORBOREMA PROVINCE: DOUBLE VERGENCE IN RESPONSE TO OBLIQUE COLLISION BETWEEN THE SÃO FRANCISCO CRATON AND PERNAMBUCO-ALAGOAS TERRANE. Double-vergent structures are recognized in Precambrian and Phanerozoic orogenic belts due strain partitioning in thrust and transcurrent components in transpressional sites. The Sergipano Fold Belt is an important crustal segment, located in the southern Borborema Province, NE Brazil. Meso and microscopic kinematic and geometric analysis in the northeastern portion of the Sergipano Fold Belt revealed the presence of four deformation stages (Dn, D1, D2 e D3). They resulted in inversion of tectonic vergence and imbrication of the metavolcanosedimentary sequences. The Jirau do Ponciano Dome represents the gneissic-migmatitic basement, preserving the older fabric. The later stages (D1 and D2), corresponds to thrust tectonics, represented by the Jacaré dos Homens, Belo Monte-Jeremoabo and Palmeira dos Índios shear zones and the transcurrent/transpressional stage, respectively. All this set is later affected by a ductile-brittle phase (D3), responsible for fractures, faults and formation of breccias. The integration of the obtained data suggest that the area framework was developed in distinct contractional episodes and reworked in the Late Neoproterozoic, in response to oblique collision between the Pernambuco-Alagoas terrane/block and the São Francisco Craton.Keywords: Orogenic belts, double vergence, Sergipana belt

scholarly journals The Dabie Extensional Tectonic System: Structural Framework

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Quanlin Hou ◽  
Hongyuan Zhang ◽  
Qing Liu ◽  
Jun Li ◽  
Yudong Wu
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Ultrahigh Pressure ◽  
Metamorphic Complex ◽  
The South ◽  
Magma Intrusion ◽  
The North ◽  
Extensional Tectonic ◽  
Mechanism Transition ◽  
Tectonic System

A previous study of the Dabie area has been supposed that a strong extensional event happened between the Yangtze and North China blocks. The entire extensional system is divided into the Northern Dabie metamorphic complex belt and the south extensional tectonic System according to geological and geochemical characteristics in our study. The Xiaotian-Mozitan shear zone in the north boundary of the north system is a thrust detachment, showing upper block sliding to the NNE, with a displacement of more than 56 km. However, in the south system, the shearing direction along the Shuihou-Wuhe and Taihu-Mamiao shear zones is tending towards SSE, whereas that along the Susong-Qingshuihe shear zone tending towards SW, with a displacement of about 12 km. Flinn index results of both the north and south extensional systems indicate that there is a shear mechanism transition from pure to simple, implying that the extensional event in the south tectonic system could be related to a magma intrusion in the Northern Dabie metamorphic complex belt. Two 40Ar-39Ar ages of mylonite rocks in the above mentioned shear zones yielded, separately, ~190 Ma and ~124 Ma, referring to a cooling age of ultrahigh-pressure rocks and an extensional era later.

scholarly journals Structural analysis of the Rio Preto fold belt (northwestern Bahia / southern Piauí), a doubly-vergent asymmetric fan developed during the Brasiliano Orogeny

2014 ◽  
Vol 86 (3) ◽  
pp. 1101-1113 ◽  
Author(s):  
FABRÍCIO A. CAXITO ◽  
ALEXANDRE UHLEIN ◽  
LUIZ F.G. MORALES ◽  
MARCOS EGYDIO-SILVA ◽  
JULIO C.D. SANGLARD ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Structural Evolution ◽  
Shear Zones ◽  
Central Compartment ◽  
Strike Slip ◽  
Fold Belt ◽  
Main Structure ◽  
The North ◽  
Brasiliano Orogeny ◽  
Analog Models

The Rio Preto fold belt borders the northwestern São Francisco craton and shows an exquisite kilometric doubly-vergent asymmetric fan structure, of polyphasic structural evolution attributed exclusively to the Brasiliano Orogeny (∼600-540 Ma). The fold belt can be subdivided into three structural compartments: The Northern and Southern compartments showing a general NE-SW trend, separated by the Central Compartment which shows a roughly E-W trend. The change of dip of S2, a tight crenulation foliation which is the main structure of the fold belt, between the three compartments, characterizes the fan structure. The Central Compartment is characterized by sub-vertical mylonitic quartzites, which materialize a system of low-T strike slip shear zones (Malhadinha – Rio Preto Shear Zone) crosscutting the central portion of the fold belt. In comparison to published analog models, we consider that the unique structure of the Rio Preto fold belt was generated by the oblique, dextral-sense interaction between the Cristalândia do Piauí block to the north and the São Francisco craton to the south.

scholarly journals Reconciling Pan-Arabism and Pan-Africanism: The North African Leadership Dilemma

2019 ◽  
Vol 3 (1) ◽  
pp. 1-32
Author(s):  
Radwa Saad
Keyword(s):  
Civil War ◽  
Effective Leadership ◽  
The State ◽  
North African ◽  
The North ◽  
Pan African ◽  
Pan Africanism ◽  
African Leadership ◽  
Arab Israeli Conflict

The purpose of this research to examine the challenges Arab leaders face in simultaneously adhering to Pan-Arabism and Pan-Africanism and extract conditions in which the two ideologies can be reconciled to produce mutual benefits. This study poses the question: what strategies do North-African leaders deploy to balance their Pan-Arab and Pan-African commitments and what repercussions do these strategies have on the state of Arab-African relations? By drawing on two scenarios where Pan-Arabism and Pan-Africanism conflicted, namely the 1967-1979 Arab-Israeli Conflict and the 2011 Libyan civil war, it will highlight the role leadership can play in mediating such tensions. The study finds that it is only through the decrease of hegemonic pursuits and the increase in effective leadership processes both domestically and regionally that the two ideologies can coexist.

scholarly journals Lithospheric and sublithospheric deformation under the Borborema Province of northeastern Brazil from receiver function harmonic stripping

Solid Earth ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 893-905 ◽  
Author(s):  
Gaelle Lamarque ◽  
Jordi Julià
Keyword(s):  
Lithospheric Mantle ◽  
Seismic Anisotropy ◽  
Receiver Function ◽  
Seismic Station ◽  
Atlantic Coast ◽  
Shear Zones ◽  
Receiver Functions ◽  
Azimuthal Anisotropy ◽  
Northeastern Brazil ◽  
Borborema Province

Abstract. The depth-dependent anisotropic structure of the lithosphere under the Borborema Province in northeast Brazil has been investigated via harmonic stripping of receiver functions developed at 39 stations in the region. This method retrieves the first (k=1) and second (k=2) degree harmonics of a receiver function dataset, which characterize seismic anisotropy beneath a seismic station. Anisotropic fabrics are in turn directly related to the deformation of the lithosphere from past and current tectonic processes. Our results reveal the presence of anisotropy within the crust and the lithospheric mantle throughout the entire province. Most stations in the continental interior report consistent anisotropic orientations in the crust and lithospheric mantle, suggesting a dominant northeast–southwest pervasive deformation along lithospheric-scale shear zones developed during the Brasiliano–Pan-African orogeny. Several stations aligned along a northeast–southwest trend located above the (now aborted) Mesozoic Cariri–Potiguar rift display large uncertainties for the fast-axis direction. This non-azimuthal anisotropy may be related to a complex anisotropic fabric resulting from a combination of deformation along the ancient collision between Precambrian blocks, Mesozoic extension and thermomechanical erosion dragging by sublithospheric flow. Finally, several stations along the Atlantic coast reveal depth-dependent anisotropic orientations roughly (sub)perpendicular to the margin. These results suggest a more recent overprint, probably related to the presence of frozen anisotropy in the lithosphere due to stretching and rifting during the opening of the South Atlantic.

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