Instituto Dom Luiz - IDL
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Established in 1853 as the first Portuguese Meteorological and Geophysical Observatory, Instituto Dom Luiz (IDL) has developed into an integrated Earth System Institute, with research in solid Earth, Ocean and Atmospheric processes, their interactions, and their relevance for a sustainable society. IDL hosts a vibrant community, that include Geologists, Physicists, Mathematicians and Engineers, pursuing research within international collaborations, all focused in contributing to leading scientific journals in their fields, from geological to human timescales. Visit our website for more information.
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- 57Fe Mossbauer spectroscopy study of the correlation between the Fe3+ content and the magnetic properties of natural Cr-spinelsPublication . Waerenborgh, João C.; Figueiras, Jorge; A., Mateus; A. Gonçalves, MárioBoth the Fe oxidation degree and the magnetic properties determined by 57Fe Mössbauer spectroscopy were used to characterize the Cr-spinels from the Beja-Acebuches Ophiolite Complex (SE Portugal). Two different types of Cr-spinel were observed. The first one has an average Fe3+/(Fe total) ≈ 25%, and corresponds to unaltered Cr-spinel grains which remain paramagnetic down to 6K. The second one results from the alteration of the first type, has an average Fe3+/(Fe total) ≈40% and order magnetically between 222 K and 78 K. Fe3+/(total Fe) increases with the magnetic ordering temperature. The grain population ordering at the highest temperatures, in the range 202–222K, has the highest Fe3+/(total Fe) ≈ 58%. Quantitative Fe site distributions can be obtained from room-temperature Mössbauer data if the different recoilless factors for tetrahedral Fe2+ and octahedral Fe3+ are considered. The observed second-order Doppler shifts are consistent with Mössbauer temperatures of 330K and 605K, reported in the literature for tetrahedral Fe2+ and octahedral Fe3+ in other oxide spinels. The differences in the magnetic ordering temperatures allowed the characterization of both types of Cr-spinels using a single Mössbauer absorber, thus avoiding the need to separate them physically, which, in this case, would be very difficult. The results are compared to those obtained for other Cr-spinels and, for the first time in the case of natural Cr-spinels, the increase of their magnetic ordering temperatures with their oxidation degree, resulting from natural processes, is discussed in terms of the magnetic exchange interactions between the Fe cations.
- Geodynamic evolution of the South Variscan Iberian Suture as recorded by mineral transformationsPublication . Figueiras, Jorge; A., Mateus; A. Gonçalves, Mário; Waerenborgh, João; Fonseca, PauloNew structural, petrographic, mineralogical and geochemical data from the Beja-Acebuches Ophiolite Complex (BAOC) are presented, and reviewed together with data published elsewhere. The new data obtained shed light on questions such as: 1) the relative importance of the obduction event; 2) its geological record in the deep levels of BAOC; 3) the nature and intensity of the Variscan metamorphism and deformation during subsequent continental (arc) collision; 4) the age relationships between BAOC and the Beja Igneous Complex; and 5) by means of numerical modelling, the thermal metamorphism of the Ossa-Morena autochthonous terranes induced by the ophiolite obduction. The emerging picture is that of a fairly simple overall geological evolution for BAOC, seamlessly integrated within the evolution of the southern branch of the Iberian Variscides. Obduction of BAOC is a relatively minor early event in the general NE–SW convergence that gave rise to the orogen as seen regionally and is recorded by an anisotropic, high-temperature, metamorphic fabric at the gabbro levels and by subtle features of the chemical composition of primary minerals at the underlying peridotite level; it caused chilling of the obducted ophiolitic slab and no significant metamorphism on the autochtonous rocks of the Ossa-Morena Zone. BAOC underwent most of its deformation and (amphibolite facies) metamorphism during a later collisional event, that took place as the most primitive rocks of the Beja Igneous complex were being intruded, and whose waning stages are responsible for extensive serpentinisation of peridotites and for important aquocarbonic fluid discharges along the semibrittle–brittle shear zones meanwhile developed.
- Strain partitioning in transpressive shears zones in the southern branch of the Variscan Ibero-Armorican arcPublication . Dias, R; A., Mateus; Ribeiro, AntonioThe Torre de Moncorvo region (NE Portugal) is a key-sector of the Autochthon Domain of the Iberian Terrane. The region experienced Variscan deformation in the southern branch of the Ibero-Armorican Arc wherein the early structures (of Upper Devonian age—D1) denotes the establishment of a heterogeneous sinistral transpressive regime. This regime was also responsible for the development of large-scale left-lateral shear zones whose direction is subparallel to major folds. Finite strains analyses were carried out in the Torre de Moncorvo region using the normalised Fry method on different strain markers: (1) distribution of detrital quartz grains in quartzite rocks of Arenigian–Lanvirnian age; (2) arrangement of oolites in discontinuous Ordovician–Silurian ironstone horizons; (3) the rotation experienced by Skolithos preserved in Lower Ordovician metasedimentary clastic rocks. The results obtained indicate the predominance of slightly prolate strain ellipsoids. Nevertheless, the variation of their orientation around mesoscopic folds emphasises the role of strain partitioning in a transpressive regime, suggesting that different folding mechanisms were active in the course of the same deformation phase. For the studied cases, tangential longitudinal strain and flexural shear combined with regional sinistral shear seem to be the most common mechanisms of folding. Some of these three-dimensional theoretical models for strain patterns in folds could be used in other regions, where a transpressive regime is inferred.
- Variscan overthrusting, fluid flow and the genesis of magnetite ore-bodies at Azenhas area (Pedrógão, Ossa-Morena Zone, SE Portugal)Publication . A., Mateus; Araújo, A; A. Gonçalves, Mário; Matos, JIn the Azenhas area (SE Portugal), an important segment of a regional WNW-ESE Variscan thrust can be observed. The hanging wall felsic metavolcanics carried from ENE are evolved rhyolite tuffs. The underlying sequence is mainly composed of variably metasomatised allochthonous amphibolites that are believed to represent an ophiolite slice tectonically overlying the autochthonous Moura-Ficalho Complex. Within this latter sequence, numerous WNW-ESE thrusts with prevailing displacement towards W-SW cut prior sub-parallel structures with northwards thrust shear. According to the observed crosscutting relationships and to the available petrographic data, the metasomatism experienced by the lower amphibolite sequence took place mainly before the emplacement of the upper slices of amphibolites, preceding therefore the installation of the felsic metatuffs. Magnetite ore-bodies are found within strongly metasomatised amphibolites immediately below the major WNW-ESE thrust zone or its subsidiary thrust structures. Their genesis is envisaged as a result of a complex chemical reaction path that involves the ascent of aqueous oxidising fluids under a reverse temperature gradient generated during the tectonic emplacement of amphibolites. In order to test the geological plausibility of the thermal evolution and the time span needed for ore genesis a one-dimensional numerical model was developed. This model enables the tracing of vertical thermal profiles at different times and accounts for the thrust emplacement history, incorporating variable erosion rates of the rock sequence. The results obtained show that an inverted thermal gradient in the thrusted sequence is kept for over 1 Ma and a regular temperature increase (from 400ºC to 500ºC) is observed in the underlying rocks lasting for 4.5 to 5.5 Ma.
- The Beja Layered Gabbroic Sequence (Ossa-Morena Zone, Southern Portugal): geochronology and geodynamic implicationsPublication . Jesus, AP; Munhá, J.; A., Mateus; Tassinari, C.; Nutman, A. P.The Beja Igneous Complex (BIC) is a major geological feature in SW Iberian Variscides, consisting of three main units developed during different stages of the oblique collision between the Ossa Morena Zone (OMZ) upper plate and South Portuguese Zone (SPZ) lower plate, namely: (1) ca. 355 Ma to ca. 345 Ma Layered Gabbroic Sequence formed in early stages of collision magmatism; (2) the ca. 335-330 Ma to ca. 320 Ma Cuba-Alvito (gabbro-diorite) Complex formed throughout the late-collision magmatic event; and (3) the Baleizão Porphyry Complex corresponding to the period of post-collision magmatism, ca. 300 Ma. The new SHRIMP U-Pb age of 342±9 Ma reported here for amphibole-bearing pegmatite dykes cutting the layered gabbros is interpreted as dating the development of late fluid-rich melts in the Layered Gabbroic Sequence, synchronous with Fe-Cu-Co sulphide deposition. The close agreement between this data and available amphibole 40Ar/39Ar ages of BIC, Beja-Acebuches Ophiolite and other geological units of the OMZ southern border, may be taken as evidence for a moderate to rapid regional crustal uplift episode at ca. 340±5 Ma; this data, coupled with structural constraints, also allow to estimate the age for the transition between the D2a – D2b deformation phases of Variscan continental collision. A complex wedge system within the SW Iberian Variscides developed during this collision, involving the OMZ upper plate to the north and the SPZ passive margin in the lower plate. The Évora-Beja-Aracena Domain, located in the upper plate above the N-dipping subduction zone, is re-interpreted as a retro-wedge domain that was kinematically coupled to the SPZ pro-wedge and subduction system. Retro-wedge growth is linked to upper plate uplift (early collision) and a late-orogenic wedge thickening. The early stages of magmatism in the retro-wedge are related to asthenospheric mantle upwelling induced by the slab break-off. Regional LP-HT metamorphism and subsequent magmatic events in the retro-wedge domain were caused by long term high heat flow sustained by (1) mafic magma underplating, (2) stacking of high-heat producing upper-crustal lithologies, and reinforced (3) by (moderate to) rapid crustal uplifting. Mass advection and orogenic architecture were strongly affected by asymmetric removal towards the lower-part foreland basin and by transient mechanical properties of the wedge system associated with the anomalous thermal regime.
- Interplate versus intraplate strike-slip deformed belts: examples from SW IberiaPublication . Romão, J.; Ribeiro, Antonio; Pereira, E.; Rodrigues, J.; A., Mateus; Noronha, F.; Dias, R.A complete transition in tectonic style between pure thrust belts and pure strike-slip beltscan be envisaged, both in interplate and intraplate settings, by a combination of thrust and strike-slipcomponents of displacement. The accommodation of shortening components in strike-slip deforma-tion belts has been discussed recently on the basis of two alternative perspectives: (1) the “sub-horizon-tal attachment model”, where discrete strike-slip faulting of rigid blocks in the schiszosphere evolves tocontinuous movement in plastosphere through a bottom-up driving mechanism controlled by verticalcoupling across the lithosphere, and (2) the “accommodation model” that considers decoupling with-in a heterogeneous and anisotropic plastosphere. Two examples of variable shortening componentaccommodation in strike-slip deformation belts of the SW Iberia Variscides are reported and discussed.In the Tomar-Badajoz-Córdoba shear zone, an important shortening component is accommodated inflat-lying bends around the horizontal axis within a WNW-ESE flower-structure with sinistral strike-slip component; the geodynamic evolution points to an intraplate setting for this structure. In the N-S, Porto-Tomar-Ferreira do Alentejo, dextral shear zone, the shortening component is restricted torestraining bends around the vertical axis; the geodynamic evolution allows inferring a transformnature for this structure, thus indicating an interplate setting. For these examples, the “accommodationmodel” is preferred to the “sub-horizontal attachment model”
- Main characteristics and genesis of the Vale de Pães skarn (Cuba-Vidigueira, Ossa Morena Zone, Portugal)Publication . Salgueiro, R.; Inverno, C.; A., MateusThe Vale de Pães (Cuba-Vidigueira) mineralisation is composed of magnetite ± sulphides and hosted in a Pre-Variscan metamorphic sequence intruded by igneous rocks belonging to the Beja Igneous Complex. Its mineral and chemical features are compatible with a zoned Fe-skarn: Mg-rich (Fo + Di90, oxidised) and Ca-rich (Grs + Di81-39, oxidised or relatively reduced). In the Fe-Mg skarn, magnetite deposition occurred along with the anhydrous mineral assemblage at ≈ 600 °C; sulphides precipitated from the retrograde stage onset (≤ 550 °C) and during the hydrated and carbonate phases formation period (< 420 °C). In the Fe-Ca skarn, magnetite precipitated during the retrograde stage (< 550 °C) together with the hydrated mineral association, and was followed by sulphides at ≈ 400°C. The mineralising process involved moderate-high salinity fluids and was controlled by variations in redox potential and pH.
- Science Education in a Museum: Enhancing Earth Sciences Literacy as a Way to Enhance Public Awareness of Geological HeritagePublication . Reis, J.; Póvoas, L.; J A S Barriga, Fernando; Lopes, C.; Santos, V. F.; Ribeiro, B.; Cascalho, João; Pinto, A.Today, scientific literacy has become increasingly important as a hallmark of citizenship and as a way to facilitate many of life’s daily decisions. Scientific literacy can be achieved through learning, a complex lifelong process that occurs both in school and out-of-school settings. As most adults only engage in formal education about science during compulsory schooling, all the learning that people go through in out-of-school settings and beyond compulsory schooling becomes extremely important toward the scientific literacy of the individual. The learning process in out-of-school settings requires interest from each person and can be facilitated by various agents, for example, museums. This is particularly true for Earth sciences as Geology topics are rarely taught within the science curricula during school. The Museu Nacional de História Natural e da Ciência provides realistic experiences that engage different publics into science and thus enhances the public science literacy. It is expected that by enhancing people’s Earth sciences literacy, it will also enhance their awareness of geological heritage.
- Permian-Triassic maturation and multistage migration of hydrocarbons in the Assistência Formation (Irati Subgroup), Paraná Basin, Brazil: implications for the exploration modelPublication . A., Mateus; Riccomini, Claudio; Ferreira, Ezequiel J. E. C. B.; Tassinari, Colombo C. G.New lines of geological evidence strongly suggest that the main period of hydrocarbon maturation within Assistência Formation should be Permian-Triassic, stimulated by a high geothermal gradient that also sustained various manifestations of hydrothermal activity. Three main stages of fluid/hydrocarbon migration can also be inferred on the basis of multiscale observations: confined flow in late Permian to Triassic times, depending on the local build-up of fluid pressures; heterogeneous flow in Lower Cretaceous, triggered by a rejuvenated temperature gradient assisted by the early developed permeability conditions; and a late flow possibly driven by local pressure gradients, after complete cooling of dolerite dykes/sills. The early maturation and multistage migration of hydrocarbons have significant consequences in the design of exploration models to be applied in Paraná Basin.
- Water prospection in volcanic islands by Time Domain Electromagnetic (TDEM) surveying: The case study of the islands of Fogo and Santo Antão in Cape VerdePublication . Martínez-Moreno, F.J.; Monteiro Santos, Fernando Acácio; Madeira, J.; Bernardo, I.; Soares, A.; Esteves, M.; Adão, F.Water demand in islands, focused in agriculture, domestic use and tourism, is usually supplied by groundwater. Thus the information about groundwater distribution is an important issue in islands water resources management. Time Domain Electromagnetic (TDEM) provides underground resistivity distribution at greater depths and is of easier application than other methods. In this study TDEM technique was used for groundwater prospection in two volcanic islands with water supply problems, the islands of Fogo and Santo Antão in the Republic of Cape Verde. The 10 islands of Cape Verde Archipelago, located off the coast of Senegal (W Africa), present a semi-arid climate and thus suffer from irregular and scarce precipitation. In the Island of Fogo 26 TDEM soundings, presenting an area distribution, were performed on the SW flank of the volcanic edifice. These allowed obtaining a 3D model composed of 5 layers parallel to the topographic surface separated by 50 m depth down to − 250 m. The results indicate the presence of the water-table at a depth of 150 m in the lower ranges of the W flank of the island, and at > 200 m depth in the area above 250 m above sea level (a.s.l.). In the Island of Santo Antão 32 TDEM soundings, distributed along 5 linear profiles, were obtained on the north-eastern half of the island. The profiles are located in two regions exposed to different humidity conditions to the N and S of the main water divide. The northern flank receives the dominant trade winds first and most of the precipitation and, therefore, the water-table is shallower (~ 50 m depth) than in the S (~ 100 m depth). Our study demonstrates the applicability and usefulness of the TDEM method for groundwater prospection in high resistivity contexts such as in volcanic islands.