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- Exhumation of an anatectic complex by channel flow and extrusion tectonics: structural and metamorphic evidence from the Porto–Viseu Metamorphic Belt, Central-Iberian ZonePublication . M. Bento dos Santos, Telmo; Rodrigues, José Feliciano; Castro, Paulo; Cotrim, Beatriz; Pereira, Inês; Ferreira, Joana; Pinto De Meireles, Carlos Augusto; Ferreira, Narciso; Ferreira, Priscila; Ribeiro, António; Guimarães, FernandaAbstract: Structural and metamorphic analyses of the Porto–Viseu Metamorphic Belt (PVMB), an anatectic complex located in the Central-Iberian Zone (CIZ), Iberian Variscan Massif, constrain the kinematic features of the polyphase Variscan deformation, as well as the boundary conditions associated with the exhumation and emplacement of the belt onto the CIZ’s lower-grade metasediments. A sharp metamorphic contrast is evident between the lowest grade rocks of the anatectic complex—garnet-staurolite mylonitic schists with a minimum metamorphic peak at P = 5.7 kbar and T = 635 °C—and the host chlorite-biotite metasediments of the CIZ. Additional P–T estimates for metatexites in the PVMB provided P = 7.6–7.9 kbar and T = 770–810 °C, confirming high-grade metamorphic peak conditions. The temperature jump between the anatectic complex and the low-grade host rocks exceeds 400 °C if the anatectic core of the belt (metatexites, diatexites, and S-type granites) is considered, implying a vertical difference of 10–17 km. The PVMB is limited in the NE by a D2 shear zone displaying normal kinematics, which has been explained so far by extensional tectonics. However, the SW boundary is limited by a D2 shear zone showing reverse kinematics. This pair of coeval and antithetical ductile shear zones bordering the PVMB, associated with the increase of the metamorphic grade towards the axial domain of the belt, is consistent with anatectic channel flow, followed by extrusion tectonics of the PVMB within an overall D2 compressive setting.
- Recursos geológicos e o ordenamento do território : o exemplo do PDM de BragançaPublication . Pinto de Meireles, Carlos Augusto
- Cronoestratigrafia do Ordovícico em Portugal: que escala utilizar?Publication . Sá, Artur Abreu; Gutiérrez-Marco, Juan Carlos; Pinto de Meireles, Carlos Augusto
- A Casa das Pedras em Montesinho, Bragança : aproveitamento didáctico de uma colecção particular de rochas locaisPublication . Meireles, Carlos; Esteves, Eduardo
- Uma proposta metodológica para o capítulo da geomorfologia de uma Notícia Explicativa de uma folha da Carta Geológica de Portugal (1:50 000)Publication . Marques, Eliane; Pinto de Meireles, Carlos Augusto
- U-Pb detrital zircon ages in synorogenic deposits of the NW Iberian Massif, Variscan belt : interplay of Devonian-arboniferous sedimentation and thrust tectonicsPublication . Martínez Catalán, José R.; Fernández-Suárez, Javier; Pinto de Meireles, Carlos Augusto; González-Clavijo, Emilio J.; Belousova, Elena; Saeed, AyeshaDetrital zircons from Devonian and Carboniferous synorogenic flysch deposits occurring in an imbricate stack have been dated by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) to: (1) obtain a maximum depositional age to constrain the maximum age limit for thrusting of exotic terranes in the NW Iberian Massif; (2) correlate the zircon age populations with published ages in nearby units to establish their possible source areas. The maximum depositional ages are Late Devonian for rocks high in the structural nappe pile (Gimonde Formation), in accordance with palynomorph dating, and around the Devonian–Carboniferous boundary for structurally lower samples (San Vitero Formation). Used in conjunction with previously published ages, the new ages are interpreted in terms of the advance of the thrust system responsible for the emplacement of exotic terranes upon the Iberian autochthon during the Variscan collision. Early Variscan zircon population ages indicate the exotic terranes as the source of synorogenic sediments, whereas their scarcity suggests derivation from the Iberian autochthon. One of the samples analysed lacks Variscan detrital zircons; this feature, together with the absence of an Early Palaeozoic zircon age population, puts into question its synorogenic character and suggests that the sample may be representative of the preorogenic parautochthon.
- Organização tectonoestratigráfica do complexo parautóctone do NE de Portugal : uma propostaPublication . Rodrigues, J.; Ribeiro, António; Pereira, Eurico; Pinto de Meireles, Carlos AugustoCom base em características geométricas e estratigráficas apresenta-se, para o NE de Portugal, uma divisão interna no Complexo Parautóctone: o Parautóctone Inferior está estruturado num conjunto interno de acidentes inversos imbricados envolvendo unidades silúrico-devónicas; o Parautóctone Superior apresenta macrogeometrias do tipo manto-dobra, com flancos inversos que podem apresentar mais de 10 km de extensão e unidades com possível idade ordovícica no núcleo de grandes anticlinais deitados e vergentes para E a SE.
- Interesse patrimonial dos aspectos geológicos e geomorfológicos da região de Aveleda-Baçal, Parque Natural de Montesinho, NE de PortugalPublication . Pinto de Meireles, Carlos Augusto; Pereira, Diamantino Ínsua; Alves, Maria Isabel C.; Pereira, P.O Parque Natural de Montesinho (PNM) fica situado no Nordeste de Portugal, abrange a parte norte dos concelhos de Vinhais e Bragança e engloba as serras da Coroa e Montesinho. Geologicamente o PNM situa-se nas unidades autóctones da Zona Centro Ibérica e nas unidades parautóctones e alóctones da Zona Galiza-Trás-os-Montes. Nesta primeira abordagem acerca do Património Geológico do PNM, faz-se a análise da região situada entre Aveleda e Baçal, cuja clareza das formas de relevo e a definição das relações com a geologia e com a tectónica, no seio de uma área protegida, são razões para a sua valorização. Assim, no presente trabalho descrevem-se e interpretam-se os aspectos geomorfológicos desta região. A partir de locais de observação estabelecidos é possível constatar que a região de Aveleda-Baçal corresponde ao bloco abatido de um graben controlado por falhas de orientação NNE-SSW, com destaque para a falha de Portelo que origina uma escarpa pelo soerguimento do bloco ocidental e abatimento a leste. No bloco ocidental deste acidente tectónico estão representados restos de uma superfície de aplanamento a cotas superiores a 900 metros (superfície de Espinhosela) e para norte a serra de Montesinho (1481 m), um bloco mais elevado de topos relativamente aplanados.
- Metamorphic and geodynamic evolution of the high-grade units of Mundão-Sátão (Northern Portugal)Publication . Castro, Paulo Ferreira; Bento dos Santos, Telmo; Pinto de Meireles, Carlos Augusto; Sequeira, António J. D.; Ferreira, Narciso
- The written stones of the Montesinho Natural Park : where palaeontology meets popular legendPublication . Sá, Artur Abreu; Gutiérrez-Marco, Juan Carlos; Pinto de Meireles, Carlos AugustoDeep in the memory of the inhabitants of the region of Montesinho (NE Portugal), there is a legend which talks about the existence of enigmatic pedras escrevidas (="written stones") in the mountains near the village of Guadramil. In the first half of the 20th Century, what used to be considered some kind of rock engravings in quartzite, were studied by archaeologists, which interpreted these signs as a kind of very old (and unknown) pre-Roman writing. A modern geological mapping of the area of the Montesinho Natural Park allowed us to rediscover the original sites of these structures and interpret them as ichnofossils. They occur on the Lower Ordovician quartzites, towards the top of the lower member of the Marao Formation (Floian), which crops out extensively in the area, generating the mountainous relief of the Barreiras Brancas-La Culebra sierra. The study of the locality required two excavating campaigns, supported by the Portuguese Ministry of Science, which involved 40 highschool students during the summer of 2002 and 2003 in an area located 5 km north of Guadramil and very close to the Spanish border. It resulted in the exposure and cleaning of an exceptional surface of 40 square meters with a very vast ichnofossil accumulation, reaching a maximum of 2,000 individual specimens by square metre. All of them correspond to horizontal sections of conical structures created by the spiral displacement of steeply inclined J-shaped burrows, assigned to the arthrophycid forms Daedalus halli (Rouault) and Daedalus labechei (Rouault). Both ichnotaxa are widely known in the "Armorican Quartzite" facies of the Lower Ordovician of SW Europe, where massive occurrences reflect opportunistic colonization events on storm generated sandstones. The spectacular bedding plane concentration of these conical burrows in the locality, and the good preservation of the active backfill on their typical spreite (wing-like) structure, is currently being mapped with the purpose of determining the mathematical model underlying the burrowing pattern and ecospace interaction between the sedimentivorous producers. Anyway, this outstanding palaeontological site of the "pedras escrevidas" has no other counterpart in the world, and is of undisputable value for the Iberian geological heritage. In the near future the locality will be protected and included in the touristic programmes and guides enhancing the natural heritage of the Montesinho Natural Park. The detailed ichnological study of this outcrop is being financed through the PATRIORSI project of the Spanish Ministry of Education and Science (CGL2006-07628/BTE, years 2006-2009) and by the project "Identification, Characterization and Conservation of Geological Heritage: a Geoconservation strategy for Portugal", sponsored by the Portuguese Foundation of Science and Technology (PTDC/CTEGEX/ 64966/2006, years 2006-2009).
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