Geodynamics of the eastern sector of the Arrábida chain (W Portugal)

N.º4, p.263-267The Arrábida chain - located in the southern segment of the Lusitanian basin - is a S-wards directed fold and thrust belt of Miocene age of deformation. ENE-WSW striking frontal ramps and associated folds are connected to sinistral NNE-SSW and N-S striking lateral ramps, that show left-lateral and SE-wards reverse movements. Both frontal and oblique ramps form imbricate duplexes. Constriction increases SE-wards due to the presence of a basin boundary fault (SetúbaI- Pinhal Novo fault) that acts as a buttress to the oblique thrust movement. Kilometre scale transpressive structures can be observed along the basin boundary fault. A map scale sheath fold like structure can be observed at the Viso anticline, which is a consequence of a strong anisotropy contrast of the Mesocenozoic strata.The Arrábida chain thrusts migrated backward, i.e. to the north, according to an overstep model. Detailed geometrical reconstruction and kinematic analysis of the structures of the eastern region of Arrábida (Formosinho, Vise and Serra de S. Luis anticlines) show that a thin-skinned tectonic model (Ribeiro, A. et aI., 1990) fits very well with the geometry of the structures of the Arrábida chain

Tectónica da região de Sintra

Photo-interpretation of aerial stereopairs of the Sintra region on the approx. 1/32 000 scale together with field work allowed the production of the present Tectonic Map of the Sintra region. It is now possible to separate structures which resulted from two different tectonic events: one, corresponding to the intrusion of the Late Cretaceous Sintra igneous diapir, and the other the Miocene compressive event, the most important tectonic inversion phase of the Lusitanian Basin. The former are present to the south, southeast and east of the intrusion and within the intrusion itself, affecting the peripheral granites and their contacts with the gabbro-syenite core. These structures comprehend: i) faults and conical fractures striking parallel to the massif boundary, which were intruded by dykes, ii) vertical faults and fractures of two conjugate sets, dextral NNW-SSE and sinistral NNE-SSW. These faults are certainly associated with the E-W striking massif's northwards directed thrust and indicate a N-S oriented horizontal maximum compressive stress. The Miocene compressive event reactivated most of the inherited structures as follows. The NNWSSE faults located on the Sintra southern platform were reactivated as dextral strike slip faults and the E-W thrust along the northern boundary of the massif was also reactivated. This thrust propagated to the east. It also enhanced the asymmetry of the rim-syncline, uplifted the massif and reactivated the NNE-SSW faults as sinistral lateral ramps, which also accommodated vertical throw. The present Tectonic Map of Sintra together with the available geophysical data (MOREIRA, 1984, KULLBERG et al., 1991, SILVA & MIRANDA, 1994) allowed reassessment of the models proposed for the emplacement of the Sintra, Sines and Monchique igneous massifs, which intruded during Late Cretaceous times along the deep dextral NNW-SSE oriented strike slip fault (RIBEIRO et al., 1979; TERRINHA, 1998; TERRINHA & KULLBERG, 1998)

Interpretação tectónica de um conjunto de lineamentos WNW-ESE observados em imagens landsat da margem oeste ibérica

The existence of satellite images ofthe West Iberian Margin allowed comparative study of images as a tool applied to structural geology. Interpretation of LANDSAT images of the Lusitanian Basin domain showed the existence of a not previously described WNW-ESE trending set oflineaments. These lineaments are persistent and only observable on small scale images (e.g. approx. 11200000 and 11500 000) with various radiometric characteristics. They are approximately 20 km long, trend l200±15° and cross cut any other families oflineaments. The fact that these lineaments are perpendicular to the Quaternary thrusts of the Lower Tagus Valley and also because they show no off-set across them, suggests that they resulted from intersection oflarge tensile fractures on the earth's surface. It is proposed in this work that these lineaments formed on a crustal flexure of tens ofkm long, associated with the Quaternary WNW-ESE oriented maximum compressive stress on the West Iberian Margin. The maximum compressive stress rotated anticlockwise from a NW -SE orientation to approximately WNW-ESE, from Late Miocene to Quaternary times (RIBEIRO et aI., 1996). Field inspection of the lineaments revealed zones of norm~1.J. faulting and cataclasis, which are coincident with the lineaments and affect sediments of upper Miocene up to Quaternary age. These deformation structures show localized extension perpendicular to the lineaments, i.e. perpendicular to the maximum compressive direction, after recent stress data along the West Portuguese Margin (CABRAL & RIBEIRO, 1989; RIBEIRO et at., 1996). Also, on a first approach, the geographical distribution of these lineaments correlates well with earthquake epicenters and areas of largest Quaternary Vertical Movements within the inverted Lusitanian Basin (CABRAL, 1995)

Moths and butterflies (Lepidoptera) of the continental part of the Nenets Autonomous Okrug, Russia

Until very recently, Nenets Autonomous Okrug (NAO), located in the northeastern part of European Russia, was the least studied region of Russia in terms of itsmoth fauna. Intensive sampling in the surroundings of Naryan-Mar, combined with critical revision of earlier publications and evaluation of museum collections, resulted in the discovery of a relatively rich fauna of Lepidoptera. The first regional checklist of moths and butterflies of the continental part of NAO includes 324 species (169 species of microlepidoptera and 155 species of macrolepidoptera), 178 of which are reported fromNAOfor the first time.We estimate that 40 to 180 species remain to be found in the study region. The recorded speciesmostly belong to residents of northern boreal forests and bogs. The fauna of moths and butterflies of NAO clearly differs from the fauna of Fennoscandia, due to the relatively higher proportion ofEast Palaearctic andBeringian species

Tectónica da cadeia da Arrábida

Geociências, Museu Nac. Hist. Nat. Univ. Lisboa, nº 2, 35-84A tectonic map of the Arrábida fold and thrust belt ( 30 km x 6 km) based on aerial-photo interpretation and field work is presented together with geological cross-sections constrained by seismic and gravimetric data, one restored section and kinematic models for the evolution of the Sesimbra salt-wall and the Palmela gravitational slide. Two rifting episodes of Lias-Dogger, and Malm ages, were recognized in the Arrábida rotated fault-block that were accommodated by two normal fault systems striking approximately N-S and E-W. Two episodes of tectonic inversion occurred during Miocene times (Burdigalian and Late Tortonian) during which the N-S faults were reactivated as lateral ramps and the E-W faults as thrusts that formed on a backward propagation sequence. The structure and style of deformation of the Arrábida belt were controlled by the inherited Mesozoic structure and the non-stretched basement that bounds the Arrábida block to the south and east. Although most of the inversion structure appears to be thin-skinned gravimetric modelling (SILVA, 1992) indicates some involvement of the basement in the Viso duplex. The existence of only one detachment, the Hettangian evaporite complex, whose depth to is estimated between 3.5 km and 2.2 km, as constrained by gravimetric and geometric models, is the reason for the simple and elegant geometry of the Arrábida fold and thrust belt. Shortening across the belt was estimated in e = 35% (RAMSAY, 1967) using a 10 km section drawn between Quinta do Anjo (loose line) and Albarquel (pin point) in the eastern sector of the Arrábida belt, across the Serra de São Luís and Viso structures.Apositive strain gradient from north to south and west to east is observed at cartographic scale and was corroborated by independent strain analysis ( P. RIBEIRO, et al., 1996; A. RIBEIRO, et al., 1996

Paleolítico médio em Galapos (Arrábida)

Descrevem-se artefactos líticos de quartzo (e sílex) recolhidos em Galapos (Creiro), na vertente meridional da Serra da Arrábida. São característicos do Paleolítico médio (Mustierense) e reforçam a evidência da importante ocupação humana da região, já salientada pelo estudo da gruta da Figueira Brava.info:eu-repo/semantics/publishedVersio

A sol-gel method for growing superconducting MgB2 films

In this paper we report a new sol-gel method for the fabrication of MgB2 films. Polycrystalline MgB2 films were prepared by spin-coating a precursor solution of Mg(BH_4)_2 diethyl ether on (001)Al2O3 substrates followed with annealing in Mg vapor. In comparison with the MgB2 films grown by other techniques, our films show medium qualities including a superconducting transition temperature of Tc ~ 37 K, a critical current density of Jc(5 K, 0 T) ~ 5 {\times} 10^6 A cm^{-2}, and a critical field of H_{c2}(0) ~ 19 T. Such a sol-gel technique shows potential in the commercial fabrication of practically used MgB2 films as well as MgB2 wires and tapes.Comment: 8 pages, 5 figure

Prospecção de endocarso através duma aplicação de SIG

Os parâmetros que condicionam o desenvolvimento dum carso em profundidade - endocarso - são complexos e difíceis de avaliar devido, por um lado, à diversidade e variabilidade dos factores envolvidos referentes ao meio e, por outro, à dificuldade de quantificar a sua interacção e influência no desenvolvimento da carsificação. É apresentada uma metodologia em ambiente SIG que visa a prospecção de estruturas cársicas de subsuperfície. Pretende-se efectuar, duma forma sistemática, a integração do conjunto de parâmetros que controlam o desenvolvimento deste tipo de carsificação, de forma a testar interacções e classificar áreas com maior aptidão para ocorrência de estruturas. O estudo incidiu sobre uma área piloto a Oeste de Sesimbra, região onde são conhecidas várias dessas estruturas, com particular relavância para as grutas do Zambujal2 e do Frade.publishersversionpublishe

Complexo ígneo de Sintra - um modelo de instalação constrangido por novos dados de gravimetria e ASM

Um estudo gravimétrico realizado recentemente, mostra que o maciço de Sintra é um lacólito, com espessura máxima preservada de rocha ígnea, na região central, de cerca de 1 km. Estudos de Análise da Susceptibilidade Magnética realizados na mesma ocasião em 56 sítios de amostragem no interior do maciço ígneo, põem em evidência, no que respeita à intrusão granítica, uma foliação magmática com orientação irregular e uma lineação magnética k1 com uma direcção dominante NNE-SSW, consistente com um modelo de intrusão definido por uma zona de alimentação magmática com orientação WNW-ESE, em conformidade com o alinhamento dos mínimos gravimétricos no mapa de anomalias de Bouguer construído. A intrusão gabro-sienítica carece de padrão geométrico de ASM, salvo no contacto com o granito, onde é paralela ao mesmo O valor global da susceptibilidade magnética das rochas ígneas do maciço de Sintra varia significativamente entre as fácies gabróicas (K: 72080 x 10-6 S.I.), que afloram na região mais a oeste do maciço, e as fácies sieníticas e graníticas envolventes (K: 39 x 10-6 S.I.). A intrusão do lacólito de Sintra ocorreu no Cretácico superior e foi controlada por dois conjuntos de falhas: um, de orientação NNW-SSE/90º, profundo, controlando a ascenção magmática inicial através da litosfera mais profunda e apenas localmente rompendo á superfície e, outro, de orientação WNW-ESE, controlando a instalação final do maciço. Durante o Terciário (muito provavelmente o Miocénico) o maciço de Sintra foi exumado e atingiu a sua altitude actual, devido á formação de um cavalgamento, vergente para norte, com uma direcção E-W aproximada, observável no contacto norte das rochas ígneas do maciço de Sintra com as rochas do encaixante sedimentar. Estima-se em 2 km a movimentação total no plano de cavalgamento.publishersversionpublishe