Conférence du Pr Fabricio De Andrade Caxito - CPMTC Nouvelle page 1

 
 

Conférence du Pr Fabricio De Andrade Caxito - CPMTC

 

 
 

Pr Fabricio de Andrade Caxito a présenté une conférence intitulée "Towards an integrated model of geological evolution for NE Brazil-NWAfrica: The Borborema Province and its connections to Hoggar through the Benino-Nigerian Shield and Cameroon " à la bibliothèque du CRAAG le dimanche 06 octobre 2019 à 10h00

 

 

Résumé:

Towards an integrated model of geological evolution for NE Brazil-NW Africa: The Borborema Province and its connections to Hoggar through the Benino-Nigerian Shield and Cameroon

 Fabrício de Andrade Caxito1

 1 Centro de Pesquisas Manoel Teixeira da Costa, Instituto de Geociências, Universidade Federal de Minas Gerais (CPMTC-IGC-UFMG), Campus Pampulha, Av. Antônio Carlos 6627,

CEP 31270-901, Belo Horizonte, MG, Brazil; caxito@ufmg.br

The Borborema Province of NE Brazil is a region characterized by great crustal complexity, with superposition of various deformational, metamorphic and magmatic events and main structuring during the Pan-African / Brasiliano Orogeny (ca. 625-510 Ma). The geological framework of the province is composed of: (i) a major Paleoproterozoic (2.2-2.0 Ga) basement strongly reworked during the Brasiliano Orogeny, with a few Archean nuclei including the oldest rocks in South America (ca. 3.5-3.2 Ga orthogneisses of the São José do Campestre massif); (ii) Paleo-mesoproterozoic sequences (starting at 1.8.-1.7 Ga, and anorogenic granites at ca. 1.5 Ga) developed under a continental rift setting, mainly in the Orós-Jaguaribeano belt of the Ceará Central domain; (iii) conspicuous orthogneisses of the Cariris Velhos Belt, dated at ca. 1000-960 Ma, which are characteristic of this province and not found elsewhere in the Atlantic Shield of Brazil; and (iv) the components of complete plate tectonic cycles at the Neoproterozoic, including rift and passive margin sequences (900-670 Ma) superseded by syn-orogenic sedimentary basins (< 650 Ma) throughout the province. Those are intruded by various generations of granitic and syenitic plutons, including: (i) calc-alkaline suites interpreted as related to continental magmatic arcs at ca. 640-625 Ma (Stage I, Tamboril-Santa Quitéria, Conceição-type granites, and continental arcs of the Riacho do Pontal and Sergipano belts); (ii) two-mica syn-collisional granite sheets following crustal anatexis and the peak of upper greenschist to amphibolite facies metamorphism and tangential (thrust and nappe) deformation at ca. 625-590 Ma (Stage II), marking the peak of continental collision, as also demonstrated by eclogites dated at ca. 625-610 Ma; followed by (iii) extensive late- to post-collisional high-K granitic and syenitic plutons emplaced in combined transpressional and extensional fields at ca. 590-530 Ma, during a late phase of lateral escape which produced the extensive network of shear zones that crosscut the province and characterizes the structural framework of NE Brazil. Comparisons with the geological evolution of the provinces in NW Africa are drawn and an evolutionary model for the whole Pan-African / Brasiliano affected areas in this region is tentatively proposed. While connection of the mountain chains that frame the province, bordering the eastern margin of the West African / São Luis craton (Médio Coreaú – Dahomeydes – Gourma – Pharusian) and the northern margin of the São Francisco / Congo craton (Rio Preto – Riacho do Pontal – Sergipano – Oubanguides – Central Africa) seem progressively better constrained, correlations within the interior, highly reworked and sectioned portions of both the Borborema, the Benino-Nigerian shield, Central and East Hoggar, and NW Cameroon, are more complicated and tentative scenarios demand novel geological, isotopic and geochronological data in order to be refined. Some of the questions of prime importance in this context are the continuation or not of the 1000-960 Ma Cariris Velhos belt, now well defined in Brazil, into NW Africa, where rocks of this age have not yet been described; and if the basement-dominated North Borborema / Benino-Nigerian and Central-southern Borborema / East Nigeria / NW Cameroon (?) domains could represent major metacratonic blocks such as LATEA. Discover and characterization of key tectonic units, such as ophiolites, eclogites, HP/UHP rocks, and both oceanic and continental magmatic arcs are helping to clarify those issues and no doubt will have an enormous impact in tectonic models for the geological evolution of NE Brazil / NW Africa in the near future.            

 

 

 

 

 

 


 

 
     

 

 

 

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