O fosso da Ribeira de Telhares, SW de Portugal : um elemento pertencente a um alinhamento de grabens subparalelo ao sistema Arrifóias-Aljezur-Sinceira

O fosso da Ribeira de Telhares é uma depressão tectónica de direcção geral N-S e dimensão 5 X 1 km. É controlado por falhas normais longitudinais (N-S) e transversais (ENE-WSW) que, posteriormente, têm movimentação em desligamento esquerdo as longitudinais e direito as transversais. Os dois sistemas de falhas fragmentam o fosso em vários horsts e grabens menores. Os sedimentos que preenchem o fosso foram divididos em duas formações, de Telhares e de Tramagueira, que, por correlação estratigráfica, foram atribuídas ao Tortoniano Superior-Messiniano Inferior e ao Gelasiano, respectivamente. Estes depósitos sedimentares formaram-se em meio continental, com clima sub-húmido sazonal e, provavelmente, relacionados com relevos próximos. Estão parcialmente cobertos por depósitos fluviais quaternários que constituem a planície aluvial actual e por sedimentos quaternários que formam vários sistemas de terraços. Com excepção dos depósitos quaternários, os materiais da cobertura interior do fosso estão falhados e apresentam estruturas interpretadas como paleossismitos. Este fosso faz parte de um sistema de fossos subparalelo ao sistema Arrifóias-Aljezur-Sinceira, situado 25 km para

Idades preliminares U-Pb, ID-TIMS, das Ilhas Berlengas, Portugal = Preliminary ID-TIMS, U-Pb ages of the Berlengas Islands, Portugal

Apresentam-se os resultados provisórios das idades U-Pb de duas amostras das ilhas do grupo das Berlengas. No Farilhão Grande uma amostra de granito de duas micas com silimanite foi recolhida de um complexo metamórfico. Esta amostra ofereceu três fracções de monazite com idade 377+-1 Ma, interpretada como metamórfica, enquanto uma fracção de zircões de concórdia 483 Ma sugeriu uma idade Tremadoc. Esta última fracção é herdada, provavelmente do volumoso magmatismo do Ordovícico Inferior existente na Ibéria. Na Berlenga Grande o granito apresenta fracções de monazite e zircão concordantes de 307,4+-0,8 Ma.

Space and time in the tectonic evolution of the northwestern Iberian Massif: Implications for the Variscan belt.

Recent advances in geochemical studies of igneous rocks, isotopic age data for magmatism and metamorphism, quantitative pressure-temperature (P-T) estimates of metamorphic evolution, and structural geology in the northwestern Iberian Massif are integrated into a synthesis of the tectonic evolution that places the autochthonous and allochthonous terranes in the framework of Paleozoic plate tectonics. Because northwestern Iberia is free from strike-slip faults of continental scale, it is retrodeformable and preserves valuable information about the orthogonal component of convergence of Gondwana with Laurentia and/or Baltica, and the opening and closure of the Rheic Ocean. The evolution deduced for northwest Iberia is extended to the rest of the Variscan belt in an attempt to develop a three-dimensional interpretation that assigns great importance to the transcurrent components of convergence. Dominant Carboniferous dextral transpression following large Devonian and Early Carboniferous thrusting and recumbent folding is invoked to explain the complexity of the belt without requiring a large number of peri-Gondwanan terranes, and its ophiolites and highpressure allochthonous units are related to a single oceanic closure. Palinspastic reconstruction of the Variscan massifs and zones cannot be achieved without restoration of terrane transport along the colliding plate margins. A schematic reconstruction is proposed that involves postcollisional strike-slip displacement of ~3000 km between Laurussia and Gondwana during the Carboniferous

Educar para los nuevos Medios. Claves para el desarrollo de la competencia mediática en el entorno digital

Educar es una de las labores más complejas, intensas y, a la vez, más maravillosas que puede acometer una persona. Ser docente es una tarea ilusionante. En un mundo en el que la información es cada vez más importante por la rapidez con que se produce y consume, la variedad de recursos con que se difunde constituye un reto en el papel de los educadores y educadoras. La educación para la comunicación, a través de los nuevos medios, requiere de habilidades y estrategias específicas e implica prácticas innovadoras. Este texto ofrece claves para desarrollar la competencia mediática necesaria para entender, usar y comunicar en el entorno digital. Desde el concepto de competencia mediática y la escuela prosumidora se muestran experiencias y planteamientos en distintos niveles educativos y contextos curriculares que ofrecen pistas para educar a la ciudadanía. Esta alfabetización aúna la perspectiva de la experiencia de docente receptor y consumidor, atendiendo a la recepción crítica de la información, la selección y administración de la misma, el reconocimiento de valores e ideologías y la gestión emocional, junto a la elaboración y creación de contenidos

New data on the geology of the Monchique Intrusive Alkaline Complex ("SW Portugal)

Los estudios microscópicos complementarios de las rocas alcalinas han permitido confirmar la estructura anular groseramente concéntrica del Complejo de Monchique, semejante a la que presentan los complejos alcalinos coetáneos de Sintra y Sines. La zona central está constituida por sienitas nefelínicas de grano grueso, rodeadas por un anillo de sienitas nefelínicas heterogéneas de grano más fino. En esta unidad exterior, y localmente separando ambas unidades, existen cuerpos menores de rocas básicas y ultrabásicas con feldespatoides y de brechas de diferentes tipos. Su forma groseramente elíptica con eje mayor en WSW-ENE, junto con las relaciones con el encajante, permiten proponer un mecanismo de emplazamiento en los niveles altos de la corteza a favor de un conjunto de fallas de la misma dirección, posiblemente de edad varisca y reactivadas durante los primeros episodios de la orogenia alpinaComplementary microscope studies of the alkaline rocks confirm a roughly concentric structure in the Monchique Complex, similar to the coeval Sintra and Sines complexes. The central zone is made of a coarse grain nepheline syenite and is surrounded by a ring of heterogeneous nepheline syenites of finer grain size. In this rimming unit, and locally between both units, outcrop several minor bodies of basic and ultrabasic rocks with foids and related breccias of different types. The approximately elliptical shape, elongated in WSW-ENE, and the spatial relationship with the country rocks, suggest that the magma installation into the upper crustal level was favoured by a set of faults of the same direction, probably Variscan in age, which were reactivated during the early events of the Alpine orogen

Proposal of a structural setting for the giant volcanogenic massive sulphide deposit of Río Tinto, Iberian Pyrite Belt

New field reconnaissance around the Río Tinto Mine led to a better structural knowledge on the area. The improved map support a different geological evolution on this sector determined by an earlier extensional event, which probably conditioned the mineralization processes. Later compressive poly-cyclic Variscan events developed thin-skinned tectonic

Geology and structure of Rio Tinto Mine (Iberian Pyrite Belt, Spain)

The Rio Tinto mining district is regarded as the largest volcanogenic massive sulphide district worldwide, but its geologic and structural setting remains poorly disclosed. The mineralized sequence includes a lower unit of interbedded mafic volcanics, shale and conglomerate overlain by a felsic dome-sill complex. The massive sulphides occur within the felsic rocks, either as exhalative deposits on the top or as replacive masses within the volcaniclastic rocks. The present review has a special aim on structural geology bearing up a genetic model update for the ore. Regional thin-skinned tectonic was clearly identified as the leading Variscan structural style in the district. Several stocked units bounded by thrust-faults display normal polarity on structural and sedimentary criteria basis. Reconstruction of the palaeogeography prior to the tectonic stacking reveals a very extensive mineralizing syste

The Cambrian-Ordovician boundary in the Peña de Francia syncline: lithological, sedimentological and geochemical evidences

Several levels of conglomerate cropping out in the Peña de Francia syncline were previously included in the Ordovician basal unit. However, a Lower Cambrian conglomerate can be identified inside, even in the areas where the basal Ordovician unconformity is not exposed. The Cambrian conglomerate witness the filling of deep water channels by mass flow; whereas the Basal Ordovician conglomerate indicates the starting of the Ordovician transgression in a coastal environment under tides and waves regime. Sedimentary and lithological data from the conglomerates and geochemical data from interlayered slates support this interpretatio