Geology of Northern Borborema Province, NE Brazil and its correlation with Nigeria, NW Africa

The Borborema and Benin–Nigeria provinces of NE Brazil and NW Africa, respectively, are key areas in the amalgamation of West Gondwana by continental collision during the Brasiliano/Pan-African orogenies. Both are underlain by complex basement: Nigeria has c. 3.05 Ga Archaean crust but no known Palaeoproterozoic rocks >2.0 Ga; in NE Brazil, 2.6–3.5 Ga Archaean rocks form small cores within Palaeoproterozoic gneiss terrains affected by plutonism at c. 2.17 Ga. Both regions exhibit Late Palaeoproterozoic (c. 1.8 Ga) rift-related magmatism and metasedimentary sequences overlying the basement. The Seridó Group of NE Brazil (<0.65 Ga) is similar to the Igarra Sequence in SW Nigeria. The Ceará Group, which may date back to c. 0.85 Ga, is a passive margin deposit on crust thinned during initiation of an oceanic domain. In both provinces, basement and sedimentary cover were involved in tangential tectonics that resulted in crust-thickening by nappe-stacking associated with closure of this ocean. Frontal collision between c. 0.66 and 0.60 Ga later evolved to an oblique collision, generating north–south continental strike-slip shear zones at c. 0.59 Ga. In NE Brazil, the main Pan-African suture is probably buried beneath the Parnaíba Basin. The Transbrasiliano Lineament, interpreted as the prolongation of the Kandi–4°50 Lineament in Hoggar, may represent a cryptic suture

The Neoproterozoic Ceará Group, Ceará Central Domain, Ne Brazil: Depositional Age And Provenance Of Detrital Material. New Insights From U-pb And Sm-nd Geochronology

From the Archean to the end of the Neoproterozoic the Borborema Province, northeast Brazil went through a complex polycyclic geologic evolution, ending, between 660 and 570 Ma, with the Brasiliano/Pan-African orogeny that led to West Gondwana amalgamation. Evolution of the metasedimentary covers of the Province, from the beginning of their deposition up to their involvement in the Brasiliano/Pan-African collision, is a key element in understanding formation of Gondwana and in attempts in pre-drift correlation between South America and West Africa. One of these covers, the Ceará Group, is exposed in the Ceará Central domain. Aiming to unravel the history of the Ceará Group, we carried out a geochronologic study of representative samples, combining Sm-Nd isotopic data, conventional U-Pb TIMS dating of zircon and U-Pb SHRIMP age determination of detrital zircon grains. Our results show that sedimentation of the Ceará Group started around 750 Ma, following rifting of the Archean/Paleoproterozoic basement, associated with bimodal volcanism. The interlayered basic volcanic rocks, re-crystallized into garnet amphibolites, show a concordant age of 749 ± 5 Ma interpreted as the age of crystallization. About 90% of calculated Sm-Nd TDM model ages of metasedimentary rocks are Paleoproterozoic and more than 50% of the analyzed samples have TDM between 1.95 and 2.4 Ma, with strongly negative e{open}Nd, consistent with provenance mainly from the Paleoproterozoic basement. Strong contrast between Paleoproterozoic TDM with negative e{open}Nd and young TDM (Mesoproterozoic) with slightly positive e{open}Nd is interpreted as a consequence of changes in detritus provenance induced by geomorphologic alterations resulting from tectonic activity during rifting. Ages of detrital zircon grains obtained by SHRIMP U-Pb analyses show three main groups: about 1800 Ma, 1000-1100 Ma and ca. 800 Ma which corresponds to the bimodal magmatism associated, respectively to the Oro´s-Jaguaribe domain, Cariris Velhos event and Independeˆncia Group

Hercynite-quartz-bearing granulites from Brejoes Dome area, Jequié Block, Bahia, Brazil: Influence of charnockite intrusion on granulite facies metamorphism

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U-pb Age Of The Coesite-bearing Eclogite From Nw Borborema Province, Ne Brazil: Implications For Western Gondwana Assembly

The Late Neoproterozoic assembly of western Gondwana played an important role in the subduction of oceanic and continental lithospheres. Such event was also a source of arc magmatism, reworking of cratonic margins and development of ultra-high pressure (UHP) suture zones. In the Borborema province, NE Brazil, we have described for the first time UHP rocks enclosed within gneiss migmatite and calc-silicate rocks. They bear coesite included in atoll-type garnet from metamafic rocks, identified by petrographic study and Raman microspectroscopy analysis. U-Pb zircon dating of the leucosome of the migmatites and the calc-silicate rock displays, concordant ages of 639. ±. 10. Ma and 649.7. ±. 5. Ma, respectively, here interpreted as the minimum age of the eclogitization event in the region. U-Pb zircon dating of the coesite-bearing rock defined a concordia age of 614. 9. ±. 7.9. Ma that comprised the retrograde eclogitic conditions to amphibolite facies. The UHP rocks, mostly retrograded to garnet amphibolites, occur enclosed in the Paleoproterozoic continental block composed of calc-silicate rocks, migmatized sillimanite gneiss, mylonitic augen gneiss and granitic and tonalitic gneiss along a narrow N-S oriented belt between the Santa Quite´ria magmatic arc and the Transbrasiliano lineament. This block was involved in the subduction to UHP eclogite depths, and was retrogressed to amphibolite during its exhumation and thrusting. Our data indicate an important Neoproterozoic transcontinental suture zone connecting the Pharusian belt with Borborema Province, and probably with the Brasi´lia belt in central Brazil

Idade de anatexia no Complexo de Granja, Domínio Médio Coreaú (DMC), Província de Borborema (PB): dados iniciais

O Complexo Granja é formado por associações de litotipos granulíticos,gnáissico-migmatíticos, e anfibolíticos, que afloram no NW do Ceará, e constituem a infraestrutura do Domínio Médio Coreaú (DMC). Neste contexto duas unidades litoestratigraficas se destacam: i – Unidade Granulítica, composta por silimanita/cianita granada gnaisses com intercalações de ortopiroxênio-clinopiroxênio granada gnaisses; e ii – Unidade Gnáissico-Migmatítica, com biotita-hornblenda gnaisses (gnaisses-migmatitos), englobando lentes de anfibolitos. Ambas as unidades foram submetidas em graus diversificados a processo de anatexia. Com intuito de avaliar a relação entre geração dos protolitos de gnaisses e granulitos e período de metamorfismo/migmatização, foram separadas amostras de diatexitos (composição granítica) no âmbito da unidade gnáissico-migmatítica, para obtenção de datação em zircão por Laser Ablation MC-ICP-MS. Os grãos de zircão analisados exibem dois grupos de idades distintas, as quais forneceram respectivamente 2.429 ± 29 Ma e 572 ± 32 Ma. O valor de 2,4 Ga se enquadra nos limites reconhecidos por diversos autores como período de acresção e geração dos protolitos, estabelecidos para as mesmas rochas por outros métodos isotópicos (U-Pb em zircão por TIMS e Pb-Pb por evaporação de zircão em TIMS). O valor de 572 ± 32, até então inexistente por U-Pb em zircão, representa a época de metamorfismo sob condições elevadas de temperatura, culminando com fusão crustal, durante evento tectonometamórfico associado à orogênese Brasiliana/Pan-Africana (650 – 550 Ma)

Lithospheric Architecture of the Paranapanema Block and Adjacent Nuclei Using Multiple-Frequency P-Wave Seismic Tomography

We present a new P-wave seismic tomographic model for the region of the Paraná Basin and surroundings using a multiple-frequency approach, providing better resolution than previous regional studies. We processed a total of 62,692 cross-correlation delays for P, PKIKP, PcP, and PP phases distributed among 1,081 events using six different central frequencies (0.03, 0.06, 0.13, 0.25, 0.50, and 1 Hz). We merged our data with a previous multiple-frequency study of the Amazonian Craton to cover regions outside of the study area, obtaining a total of 75,187 cross-correlation delays. The data used are from the stations of the Brazilian Seismographic Network, and mainly from a temporary network (XC network) installed exclusively to study the region. The basement of the Paraná Basin is represented as a NE-SW trending P-wave high-velocity anomaly, extending from the northern limit of the basin to the southwestern border of Brazil, consistent with previous reports. The limit between this block and the São Francisco Craton is characterized by decreased amplitude of the P-wave high-velocity anomaly. Synthetic tests show that a narrow boundary between these two blocks displays the same behavior. At the southeastern portion of this anomaly, decreasing amplitude is consistent with the limit of the Luiz Alves Craton, which was also corroborated by synthetic tests. The northern portion of the Rio Apa Block agrees with a previous tomographic model, confirming that it does not extend under the Pantanal Basin, however, in our model this structure does not extend as far south. © 2021. The Authors.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]