GCG - Artigos em revistas internacionais
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- Petrogenesis of early paleozoic peralkaline rhyolites from the Macedo de Cavaleiros region (NE Portugal)Publication . Ribeiro, Maria Luísa
- A review of Alpine tectonics in Portugal : Foreland detachment in basement and cover rocksPublication . Ribeiro, António; Kullberg, Maria Carla; Kullberg, J. C.; Manuppella, Giuseppe; Phipps, S.
- Thrust tectonics in the Strandja zone : new data from the Dervent Heights, SE BulgariaPublication . Gerdjikov, Ianko; Metodiev, DanielDervent Heights are one of the least studied parts of the Strandja zone in Bulgaria. Our detailed field studies in the area of the villages of GoIiam and Valcha PoIiana show the need of revision of the earlier models for nappe tectonics in this pari of the Alpine orogenic belt. Two major units could be distinguished in the pre-Cenomanian basement - autochthon and allochthon. The autochthon is built by Variscan high-grade metamorphic rocks and not penetrativelly deformed granitoids. They are covered by low-grade Triassic metasediments. The allochthone consist of phyllite formation with early Paleozoic age, as well as the underlying carbonate and detrital metasediments. These metasediments form a mappable unit here designated as carbonate terrigeneous formation. Field data allow to reconsider the position of the abundant dolomites. It was suggested that they are forming the autochthon, but the field relations are consistent with interpreting them as a part of the carbonate-terigeneous formation. All studied rocks record very low-grade Early Alpine metamorphism (T<3OO-350'). The metasediments of the autochthon as well these of the allochthon display evidence for strong synmetamorphic deformations and because of that primary structures are not preserved. The timing of the emplacement of the allochthon is poorly constrained, but judging from the lack of localization of ductile as well as of brittle deformation along the major contacts it could be suggested that the emplacement was pre- to synmetamorphic.
- Lower Devonian faunas and palynomorphs from the Dornes Syncline, Central Iberiam Zone, Portugal : stratigraphical and paleogeographical implicationsPublication . Gourvennec, Rémy; Piçarra, José Manuel; Plusquellec, Yves; Pereira, Zélia; Oliveira, José Tomás; Robardet, MichelIn the Dornes syncline, southern Central Iberian Zone, Portugal, the uppermost levels of the Serra do Luação Formation up to now have been considered to be of Pridoli-Lochkovian? age because they lie immediately under the Dornes Formation, which is of Pragian age and is well defined stratigraphically. New paleontological elements including benthic faunas and palynomorphs allow us to confirm that the top of the Serra do Luação Formation is securely Lochkovian, for upper Lochkovian strata are present although relatively thin. The transition from the Serra do Luação to the Dornes formations and their lithostratigraphical relationship are now clear: the terrigenous succession belongs in the Serra do Luação Formation and the limestones represent the Dornes Formation. The benthic faunas clearly have North-Gondwanan affinities.
- Thermochronology of central Ribeira Fold Belt, SE Brazil : petrological and geochronological evidence for long-term high temperature maintenance during Western Gondwana amalgamationPublication . Bento dos Santos, Telmo; Munhá, José; Tassinari, Colombo C. G.; Fonseca, Paulo E.; Neto, Coriolano DiasThe studied sector of the central Ribeira Fold Belt (SE Brazil) comprises metatexites, diatexites, charnockites and blastomylonites. This study integrates petrological and thermochronological data in order to constrain the thermotectonic and geodynamic evolution of this Neoproterozoic–Ordovician mobile belt during Western Gondwana amalgamation. New data indicate that after an earlier collision stage at ~610 Ma (zircon, U–Pb age), peak metamorphism and lower crust partial melting, coeval with the main regional high grade D1 thrust deformation, occurred at 572–562 Ma (zircon, U–Pb ages). The overall average cooling rate was low (5 °C/Ma) from 750 to 250 °C (at ~455 Ma; biotite–WR Rb–Sr age), but disparate cooling paths indicate differential uplift between distinct lithotypes: (a) metatexites and blastomylonites show a overall stable 3–5 °C/Ma cooling rate; (b) charnockites and associated rocks remained at T 650 °C during sub-horizontal D2 shearing until ~510–470 Ma (garnet–WR Sm–Nd ages) (1–2 °C/Ma), being then rapidly exhumed/cooled (8–30 °C/Ma) during post-orogenic D3 deformation with late granite emplacement at ~490 Ma (zircon, U–Pb age). Cooling rates based on garnet–biotite Fe–Mg diffusion are broadly consistent with the geochronological cooling rates: (a) metatexites were cooled faster at high temperatures (6 °C/Ma) and slowly at low temperatures (0.1 °C/Ma), decreasing cooling rates with time; (b) charnockites show low cooling rates (2 °C/Ma) near metamorphic peak conditions and high cooling rates (120 °C/Ma) at lower temperatures, increasing cooling rates during retrogression. The charnockite thermal evolution and the extensive production of granitoid melts in the area imply that high geothermal gradients were sustained for a long period of time (50–90 Ma). This thermal anomaly most likely reflects upwelling of asthenospheric mantle and magma underplating coupled with long-term generation of high HPE (heat producing elements) granitoids. These factors must have sustained elevated crustal geotherms for ~100 Ma, promoting widespread charnockite generation at middle to lower crustal levels.
- Ordovician VS. "Cambrian" ichnofossils in the Armorican quartzite of central PortugalPublication . Sá, Artur Abreu; Gutiérrez-Marco, Juan Carlos; Piçarra, José Manuel; García-Bellido, Diego C.; Vaz, Nuno; Aceñolaza, Guillermo Florencio
- A new endemic spiriferid genus from the Lower Devonian of Central PortugalPublication . Schemm-Gregory, Mena; Piçarra, José Manuel
- Ordovician graptolites and acritarchs from the Barrancos region (Ossa-Morena Zone, South Portugal)Publication . Piçarra, José Manuel; Pereira, Zélia; Gutiérrez-Marco, Juan Carlos
- New insights on the Hirnantian palynostratigraphy of the Rio Ceira section, Buçaco, PortugalPublication . Lopes, Gilda; Vaz, Nuno; Sequeira, António J. D.; Piçarra, José Manuel; Fernandes, Paulo; Pereira, Zélia
- Tracing the Cadomian magmatism with detrital/inherited zircon ages by in-situ U-Pb SHRIMP geochronology (Ossa-Morena Zone, SW Iberian Massif)Publication . Pereira, M. F.; Chichorro, Martim; Solá, A. Rita; Silva, J. B.; Sánchez-García, Teresa; Bellido, F.