Petrologia e termocronologia de granulitos no sector central da Faixa Ribeira: (região de São Fidélis, Rio de Janeiro, Brasil)

Tese de doutoramento em Geologia (Geoquímica), apresentada à Universidade de Lisboa através da Faculdade de Ciências, 2008A região de São Fidelis localiza-se a norte do Rio de Janeiro (SE do Brasil) e pertence à zona central da Faixa Ribeira, uma faixa móvel de idade Neoproterozóica Ordovícica. Esta tese apresenta dados referentes a diversas metodologias com o objectivo de caracterizar a evolução dos granulitos presentes na área e, desta forma, discriminar a evolução geodinâmica da Faixa Ribeira, formada no final do Ciclo Brasiliano por colisão dos crátons de São Francisco e Congo no contexto da aglutinação do mega-continente Gondwana Ocidental. Os resultados indicam que após a colisão há 630-610Ma, o metamorfismo granulítico (T~850ºC; P~8kbar), contemporâneo de cavalgamentos de alta temperatura (no contexto da formação de uma mega-estrutura em flor), extensa migmatização de rochas supracrustais e geração de granitóides, foi atingido há ~565Ma, tendo o arrefecimento que se seguiu sido processado mais rapidamente nas rochas próximas da zona central da estrutura em flor (3 10ºC/Ma) que nas presentes nas rampas laterais (~1ºC/Ma). Uma anomalia térmica, provavelmente resultante de upwelling da astenosfera e underplating (num contexto de extensão pós-colisional), terá permitido, auxiliada pelo longo período de deformação transpressiva sub-horizontal que se seguiu, um arrefecimento muito lento e manutenção de T 650ºC para alguns granulitos durante ~100Ma. Após o longo período transpressivo (há 510 480Ma), as taxas de arrefecimento aumentaram rapidamente (8 30ºC/Ma) por exumação mais rápida relacionada com o relaxamento termo-tectónico do colapso do orógeno. A evolução termocronológica da área estudada sugere a existência de um longo período com manutenção de condições térmicas elevadas que terá condicionado tanto a evolução das condições físicas (T, P, O2, aH2O) deste segmento crustal como a formação das feições petrológicas e geoquímicas que destas dependem, sendo que a manutenção da anomalia térmica por ~100Ma terá levado a elevada desidratação da crosta inferior e produção generalizada de charnockitos na Faixa Ribeira.The São Fidelis region is located north of Rio de Janeiro (SE Brazil) and is part of the central zone of Ribeira Belt, a Neoproterozoic Ordovicic mobile belt. This thesis presents data obtained with several techniques with the purpose of characterizing the evolution of the granulites present in the area and, in this way, to constrain the geodynamic evolution of the Ribeira Belt, formed in the final stages of the Braziliano Cycle as the result of the collision between the São Francisco and Congo cratons in the Western Gondwana mega-continent amalgamation context. Results show that after the collision at 630-610Ma, granulitic metamorphism (T~850ºC; P~8kbar), coeval with high-temperature thrusts (as the result of the formation of a mega flower structure), widespread migmatization of supracrustal rocks and granitoid production, was attained at ~565Ma, and the cooling that followed was faster for the rocks closer to the centre of the flower structure (3 10ºC/Ma) than for those present in the lateral ramps (~1ºC/Ma). A thermal anomaly, probably resultant of asthenospheric upwelling and underplating (in a post-collisional extension context), allowed, aided by the long-term sub-horizontal transpressive deformation period that followed, a very slow cooling and preservation of T>650ºC for some granulites during ~100Ma. After the long-term transpressive period (at 510 480Ma), cooling rates increased rapidly (8 30ºC/Ma) by faster exhumation due to thermo-tectonic relaxation and orogenic collapse. The thermochronologic evolution of the studied area suggests a long-term maintenance of high-thermal flux, that conditioned the evolution of this crustal segment physical conditions (T, P, O2, aH2O), as well as, the petrological and geochemical features dependent. The long-term thermal anomaly that lasted ~100Ma may have led to extensive lower crust dehydration and widespread formation of charnockites in the Ribeira Belt

Inspecting zircon populations of the Iberian Pyrite Belt: tracking the Cadomian record of the South Portuguese Zone

AIMS OF THE MEETING: The scientific sessions will be focused on the Pan-African and Cadomian Orogenies recorded in North Africa and western Europe across the Ediacaran Cambrian transition and its bearing in the assembly and demise of Pannotia. Contributions dealing with structural, magmatic, provenance sources, palaeomagnetic, sedimentary, chronostratigraphic and radiometric constraints are particularly welcome. ORGANIZING COMMITTEE: J. Javier Álvaro, Instituto de Geociencias (CSIC-UCM), Spain Martim Chichorro, Universidade Nova de Lisboa, Portugal Gabriel Gutiérrez-Alonso, Universidad de Salamanca.ABSTRACT: The palaeogeographic location of the southernmost zone of the Iberian Massif, the South Portuguese Zone (SPZ), prior to the amalgamation of Pangaea is still a matter of debate. In this work, we attempt to track its palaeogeographic setting during the final stages of the Cadomian Cycle.info:eu-repo/semantics/publishedVersio

Detrital zircon similarities and dissimilarities between the Iberian Pyrite Belt, Ossa-Morena Zone and Meguma

Acknowledgement. We thank Ícaro Dias da Silva and an anonymous reviewer for their constructive comments and suggestions. We also acknowledged Jose Javier Álvaro Blasco and Laura Rincón for editorial handling. We acknowledge the support of FCT through PhD grant SFRH/BD/138791/2018 to João Lains Amaral and through project UIDB/50019/2020 to Instituto Dom Luiz.Despite the so-called exotic nature of the South Portuguese Zone relatively to the other major domains of the Iberian Massif of peri-Gondwanan affinity, Devonian detrital rocks of the oldest strata in the Iberian Pyrite Belt have a remarkable resemblance with the Ossa-Morena Zone's Neoproterozoic-Cambrian rocks and the West Meguma's Cambrian-Ordovician rocks, presenting the so-called "West African signature". Using published U-Pb detrital zircon data, we discuss the similarities and dissimilarities between the Iberian Pyrite Belt, Ossa-Morena Zone and West Meguma Terrane through multidimensional scaling, comparing them with other zones of the Iberian Massif, Saxo-Thuringian Zone, Avalonia-Ganderia, and the North African cratonic regions. Our findings show that multidimensional scaling is not entirely effective in displaying the dissimilarities between the peri-Gondwanan terranes due to the background noise caused by the overwhelming number of Cadomian-Panafrican ages. However, it becomes a powerful tool if these ages are filtered. A dominant Meguma-type provenance (Cambro-Ordovician) for the Middle-Upper Devonian rocks of the Iberian Pyrite Belt is demonstrated, mainly attending to their similar Birimian-Eburnean pattern. The possibility of minor contributions from the lower Cambrian rocks of the Ossa-Morena Zone into the Iberian Pyrite Belt quartzites is unlikely, as the latter lack the 1.9Ga peak that characterises the Ossa-Morena Zone sediments. Additionally, the remarkable similarities between Ossa-Morena Zone's and West Meguma's detrital rocks strongly suggest a similar paleogeographic setting (but diachronic) for both terrains from the Ediacaran to Lower Ordovician times relative to the North African blocks

Cadomian/Pan-African consolidation of the Iberian Massif assessed by its detrital and inherited zircon populations: is the similar to 610Ma age peak a persistent Cadomian magmatic inheritance or the key to unravel its Pan-African basement?

ABSTRACT: This work assessed the age distribution of Cadomian/Pan-African orogenic events (550-590 and 605-790Ma, respectively) in several zones of Iberian Massif by means of detrital and inherited zircon analysis compilation. Detrital zircon age spectra show that throughout the late Neoproterozoic-to-Early Ordovician era (similar to 120Ma sedimentary record), the main systematic peak occurs at similar to 610Ma, followed by peaks at typical Cadomian ages (similar to 590-550Ma). Inherited zircons incorporated in Cambrian-to-Lower Ordovician igneous rocks show typical Cadomian ages (similar to 590-550Ma) but, once again, a remarkably consistent Pan-African similar to 610Ma peak occurs. In accordance with compiled zircon data and taking into account the evidence of North African peri-cratonic inliers, Ediacaran (similar to 610Ma) zircons incorporated in Paleozoic magmas provide indirect evidence of Pan-African magmatism, suggesting that these magmas and synorogenic sediments are likely to constitute the cryptic stratigraphic infrastructure of most of the Iberian Massif. The main source of similar to 610Ma inherited zircons may be the lateral chrono-equivalents of the Saghro and Bou Salda-M'Gouna Groups (Anti-Atlas, Morocco) and/or coeval igneous rocks from West African Craton or Trans-Sahara Belt, emplaced at a stratigraphic level below the late-Ediacaran sediments of the Ossa Morena Zone and the Central Iberian Zone. Assuming that the Iberian crust is a fragment of the Pan-African orogen, a relative paleoposition situated between the West African Craton and the Trans-Saharan Belt during the Late Neoproterozoic is proposed. The closed-system behaviour of Stenian-Tonian detrital zircon ages in the Trans-Sahara Belt suggests that this mega-cordillera acted as a barrier, in paleogeographic terms, to separating the Sahara Metacraton from Iberia. In Iberia, the opening of the system to Stenian-Tonian detrital zircon during the Ordovician indicates that, at that time, the Trans-Saharan Belt had already become a vast peneplain, which favoured a large drainage system with a long-distance transport mechanism that fed the passive continental margins.info:eu-repo/semantics/publishedVersio

is the ~610Ma age peak a persistent Cadomian magmatic inheritance or the key to unravel its Pan-African basement?

Publisher Copyright: © M. Chichorro, A.R. Solá, T.M. Bento dos Santos, J. Lains Amaral, L. Crispim, 2022.This work assessed the age distribution of Cadomian/Pan-African orogenic events (550-590 and 605-790Ma, respectively) in several zones of Iberian Massif by means of detrital and inherited zircon analysis compilation. Detrital zircon age spectra show that throughout the late Neoproterozoic-to-Early Ordovician era (~120Ma sedimentary record), the main systematic peak occurs at ~610Ma, followed by peaks at typical Cadomian ages (~590-550Ma). Inherited zircons incorporated in Cambrian-to-Lower Ordovician igneous rocks show typical Cadomian ages (~590-550Ma) but, once again, a remarkably consistent Pan-African ~610Ma peak occurs. In accordance with compiled zircon data and taking into account the evidence of North African peri-cratonic inliers, Ediacaran (~610Ma) zircons incorporated in Paleozoic magmas provide indirect evidence of Pan-African magmatism, suggesting that these magmas and synorogenic sediments are likely to constitute the cryptic stratigraphic infrastructure of most of the Iberian Massif. The main source of ~610Ma inherited zircons may be the lateral chrono-equivalents of the Saghro and Bou Salda-M`Gouna Groups (Anti-Atlas, Morocco) and/or coeval igneous rocks from West African Craton or Trans-Sahara Belt, emplaced at a stratigraphic level below the late-Ediacaran sediments of the Ossa Morena Zone and the Central Iberian Zone. Assuming that the Iberian crust is a fragment of the Pan-African orogen, a relative paleoposition situated between the West African Craton and the Trans-Saharan Belt during the Late Neoproterozoic is proposed. The closed-system behaviour of Stenian-Tonian detrital zircon ages in the Trans-Sahara Belt suggests that this mega-cordillera acted as a barrier, in paleogeographic terms, to separating the Sahara Metacraton from Iberia. In Iberia, the opening of the system to Stenian-Tonian detrital zircon during the Ordovician indicates that, at that time, the Trans-Saharan Belt had already become a vast peneplain, which favoured a large drainage system with a long-distance transport mechanism that fed the passive continental margins.publishersversionpublishe

Cadomian/Pan-African consolidation of the Iberian Massif assessed by its detrital and inherited zircon populations : is the ~610Ma age peak a persistent Cadomian magmatic inheritance or the key to unravel its Pan-African basement?

Acknowledgement. Martim Chichorro is grateful for the funding provided by GeoBioTec (UIDB/04035/2020). We acknowledge the support of Portuguese Fundação para a Ciência e a Tecnologia (FCT) through PhD grant SFRH/BD/138791/2018 to João Lains Amaral. This work was funded by the FCT I.P./MCTES through national funds (PIDDAC) - UIDB/50019/2020 to Telmo M. Bento dos Santos via IDL - Instituto Dom Luiz. Geopark Naturtejo is also gratefully acknowledged for long-term logistic support. Insightful comments, suggestions and corrections provided by Josep Maria Casas and an anonymous reviewer are kindly acknowledged. Finally, the authors would like to express their gratitude to the Guest Editor.This work assessed the age distribution of Cadomian/Pan-African orogenic events (550-590 and 605-790Ma, respectively) in several zones of Iberian Massif by means of detrital and inherited zircon analysis compilation. Detrital zircon age spectra show that throughout the late Neoproterozoic-to-Early Ordovician era (~120Ma sedimentary record), the main systematic peak occurs at ~610Ma, followed by peaks at typical Cadomian ages (~590-550Ma). Inherited zircons incorporated in Cambrian-to-Lower Ordovician igneous rocks show typical Cadomian ages (~590-550Ma) but, once again, a remarkably consistent Pan-African ~610Ma peak occurs. In accordance with compiled zircon data and taking into account the evidence of North African peri-cratonic inliers, Ediacaran (~610Ma) zircons incorporated in Paleozoic magmas provide indirect evidence of Pan-African magmatism, suggesting that these magmas and synorogenic sediments are likely to constitute the cryptic stratigraphic infrastructure of most of the Iberian Massif. The main source of ~610Ma inherited zircons may be the lateral chrono-equivalents of the Saghro and Bou Salda-M'Gouna Groups (Anti-Atlas, Morocco) and/or coeval igneous rocks from West African Craton or Trans-Sahara Belt, emplaced at a stratigraphic level below the late-Ediacaran sediments of the Ossa Morena Zone and the Central Iberian Zone. Assuming that the Iberian crust is a fragment of the Pan-African orogen, a relative paleoposition situated between the West African Craton and the Trans-Saharan Belt during the Late Neoproterozoic is proposed. The closed-system behaviour of Stenian-Tonian detrital zircon ages in the Trans-Sahara Belt suggests that this mega-cordillera acted as a barrier, in paleogeographic terms, separating the Sahara Metacraton from Iberia. In Iberia, the opening of the system to Stenian-Tonian detrital zircons during the Ordovician indicates that, at that time, the Trans-Saharan Belt had already become a vast peneplain, which favoured a large drainage system with a long-distance transport mechanism that fed the passive continental margins

Insights from the felsic volcanic rocks hosting the sulphide ore of the giant Aljustrel deposit, Iberian Pyrite Belt

This is a contribution to the research project PetroGeo (LNEG)A geochronological study using SHRIMP U-Pb analysis of zircon grains has been conducted to date felsic volcanic rocks hosting the six massive sulphide deposits of the giant Aljustrel mining district in the Iberian Pyrite Belt. A multiple method age calculation approach was used to validate and ponder calculated Concordia ages (emplacement and inherited), which included weighted average, probability density peak(s), Tuff Zirc and Unmix functions. This approach was particularly useful to interpret the wide continuous single U-Pb ages (320–405 Ma) recorded in the Aljustrel volcanic rocks. The volcanic pile (>250 m) that hosts the Aljustrel deposits was emplaced between 359 and 353 Ma. Upper Devonian inheritance, representing subvolcanic activity, is well-represented in the volcanic rocks of Aljustrel (373–365 Ma). Older Devonian inherited zircon ages at 405 Ma, 388 Ma and 380 Ma were retrieved, hypothetically representing deep plutonism or other melting episodes, which suggests a long-lasting (~50 Ma) magmatic activity in the Aljustrel district. Older pre-Devonian inherited ages, uppermost Silurian and early to late Cambrian, and post-emplacement ages (~330–345 Ma) were also detected, with the latter reflecting Pb loss most likely driven by the main Variscan orogenic event. Maximum ages obtained for the volcanic rocks in the different deposits open the possibility that the last pulses of volcanic activity and subsequent deposition of the massive sulphides were diachronic in the different Aljustrel sub-basins. Additionally, results imply that, contrary to previously assumed, Gavião and São João-Moinho deposits are probably not the same ore lens disrupted by tardi-Variscan faults. This opens new opportunities for mining exploration and targeting in the Aljustrel district and points out the importance of high-resolution geochronological studies in mining and brownfield areas.info:eu-repo/semantics/publishedVersio

Detrital zircon similarities and dissimilarities between the Iberian Pyrite Belt, Ossa-Morena Zone and Meguma

Acknowledgement. We thank Ícaro Dias da Silva and an anonymous reviewer for their constructive comments and suggestions. We also acknowledged Jose Javier Álvaro Blasco and Laura Rincón for editorial handling. We acknowledge the support of FCT through PhD grant SFRH/BD/138791/2018 to João Lains Amaral and through project UIDB/50019/2020 to Instituto Dom Luiz.Despite the so-called exotic nature of the South Portuguese Zone relatively to the other major domains of the Iberian Massif of peri-Gondwanan affinity, Devonian detrital rocks of the oldest strata in the Iberian Pyrite Belt have a remarkable resemblance with the Ossa-Morena Zone's Neoproterozoic-Cambrian rocks and the West Meguma's Cambrian-Ordovician rocks, presenting the so-called "West African signature". Using published U-Pb detrital zircon data, we discuss the similarities and dissimilarities between the Iberian Pyrite Belt, Ossa-Morena Zone and West Meguma Terrane through multidimensional scaling, comparing them with other zones of the Iberian Massif, Saxo-Thuringian Zone, Avalonia-Ganderia, and the North African cratonic regions. Our findings show that multidimensional scaling is not entirely effective in displaying the dissimilarities between the peri-Gondwanan terranes due to the background noise caused by the overwhelming number of CadomianPanafrican ages. However, it becomes a powerful tool if these ages are filtered. A dominant Meguma-type provenance (Cambro-Ordovician) for the middle-upper Devonian rocks of the Iberian Pyrite Belt is demonstrated, mainly attending to their similar Birimian-Eburnean pattern. The possibility of minor contributions from the lower Cambrian rocks of the Ossa-Morena Zone into the Iberian Pyrite Belt quartzites is unlikely, as the latter lack the 1.9Ga peak that characterises the Ossa-Morena Zone sediments. Additionally, the remarkable similarities between Ossa-Morena Zone and West Meguma's detrital rocks strongly suggest a similar paleogeographic setting (but diachronic?) for both terrains from the Ediacaran to Lower Ordovician times relative to the North African blocks

New U-Pb zircon data from the Évora Massif and correlation to the Galiza-Trás-os- Montes Zone basal units

Resumo alargadoSUMMARY: We present new U-Pb zircon data from the Évora Massif (SW Ossa–Morena Zone). Série Negra paragneiss of Escoural Fm. yields a maximum depositional age of ~580 Ma. Felsic orthogneiss “leptinites” included in Escoural Fm., commonly attributed to the Precambrian, yield a concordant age of 513 ± 3 Ma. Felsic volcanics interbedded in the Monfurado Fm. and the Safira Orthogneiss show very discordant zircon ages and two systematic populations at ~510 Ma and ~460 Ma. Given the stratigraphic constraint of Monfurado Fm., both magmatic rocks are considered coeval and emplaced at ~510 Ma during the main rift-related magmatism. The ~460 Ma age is not fully understood yet. Given the differences in the ages of magmatism in the Évora Massif, recently correlated with the Lower Allochthon of Galiza-Trás-os-Montes Zone, where only late rift-related magmatism is recorded, we suggest that they represent different sedimentary basins positioned in the same paleogeographic contexts.info:eu-repo/semantics/publishedVersio