Transcurrent continental tectonics model

The Ossa-Morena Zone (SW Iberian Massif) was affected by continuous orogen-parallel transcurrent continental tectonics from the Neoproterozoic to the Carboniferous times, involving transtension (TT) and transpression (TP) processes that co-existed together, occurred separately in neighbouring regions by the means of strain partitioning or even worked diachronically. A first stage of transpression TP1 took place during the Late Neoproterozoic–Lower Cambrian as a result of Cadomian arc-continent collisional processes. Structures generated by transtension TT1 from Cambrian to Lower Devonian were related to strong lithosphere stretching responsible for the development of basins controlled by major detachments, tilting, rifting and important tectono–thermal diachronic processes. Denudation phenomena and inhibition of sedimentation related with thermal uplift (asthenosphere upwelling) and consequent subsidence caused by isostatic equilibrium, involving generalized transgressions, were processes responsible for major unconformities. The Variscan TP2-TT2 episodes that followed diachronically TP1-TT1, by maintaining the orogen- parallel transport direction, were concomitant with syntectonic deposition of continental basins in the OMZ and foreland basins in the SPZ. TT2 local transtension and tectonic exhumation of deep crustal rocks along major shear zones, favoured the opening of tectonic troughs filled up by sediments and volcanism. TP2 shortening have generated fold axes parallel to the orogen- strike and composite dissymmetric flower structures

A new model for the Hercynian Orogen of Gondwanan France

The study by Shelley and BossieÁre (2000) is an important contribution to the discussion concerning the Ibero±Armorican arc (IAA) generation model. This model comes as one of a sequence of previous ideas already published in several papers (Bard, 1971; Matte and Ribeiro, 1975; Lefort and Ribeiro, 1980; Ribeiro et al., 1980; Burg et al., 1981; Brun and Burg, 1982; Julivert, 1987; Ribeiro et al., 1990; Dias and Ribeiro, 1995; Ribeiro et al., 1995; Silva, 1997). A common feature of the interpretations in these papers is the great importance attributed to two major transcurrent faults: the dextral Porto±Tomar shear zone (PTSZ) and the sinistral Tomar±Badajoz±Cordoba shear zone (BCSZ), to explain the extension of the Iberian structures into the Armorican Massif in the form of trace the arcuate shape of the IAA

Comment on ‘‘Geodynamic evolution of the SW Europe

Ribeiro et al. [2007] have presented a geodynamic view of the SW Iberia Variscides based on data from Portugal. Their treatment of already published data is commendable, and the knowledge gained will surely encourage the discussion of the SWEurope Variscides. However, in our opinion, Ribeiro et al.’s modeling and interpretation of the Ediacaran–Lower Ordovician ( 560–470 Ma) geodynamic evolution are of limited value. In this regard, they based their analysis of the Ossa-Morena Zone (OMZ) on assumptions which are contradicted by recent published data. Ribeiro et al. ignored recent progress in the OMZ Ediacaran-Ordovician stratigraphy and, as a consequence they misunderstood the structure of domains overprinted by strong Variscan (Carboniferous) deformation and metamorphism

The monte Molião cistern Lagos, Portugal

Conhecida desde o século XIX, a cisterna de Monte Molião constitui o elemento arquitectónico mais destacado do sítio e o único equipamento putativamente público ali documentado até ao momento. A sua escavação em 2011 e 2014 permitiu obter importantes dados sobre a sua tipologia e as técnicas empregues na sua construção, bem como documentar a estratigrafia correspondente à sua colmatação. Foi assim possível determinar que esta estrutura corresponde ao modelo dito a bagnarola, de origem púnica, podendo datar-se do final da Idade do Ferro ou de Época Romana Republicana, tendo sido sujeita a reparações durante este último período. Por outro lado, o último período de utilização desta cisterna parece ter-se verificado entre o Principado de Augusto e o reinado de Tibério, seguindo-se um período de abandono e o seu eventual entulhamento, datado pelos materiais aqui estudados da segunda metade do século I.Known since the 19th century, the cistern of Monte Molião is the most notable architectural element in the site and the only likely public infrastructure identified so far in this settlement. Its excavation, undertaken in 2011 and 2014, has brought to light important data about its typology and construction techniques; a complete stratigraphic sequence corresponding to its filling has also been documented. This structure can be attributed to the so-called a bagnarola model which originated in the Punic world and could have been constructed either in the Late Iron Age or in the Roman Republican period, having also been repaired in the latter period. Its last period of use, on the other hand, seems to fall within the reign of Augustus or Tiberius, being followed by a period of abandonment and eventually by its intentional filling which, based on the material studied here, can be dated to the second half of the 1st centuryCâmara Municipal de Lago

The role of bedding in the formation of fault–fold structures,

Fold-fault structures within a major transpressional shear zone of the SW Iberian Massif were investigated by combining geological mapping, cross-section analysis and microtectonic studies. A significant example of contractional deformation is displayed in the Portalegre-Esperanc¸a Shear Zone (PESZ) where a heterogeneous Ordovician stratigraphic sequence, showing a strong competence contrast between quartzites, slates and quartzo-feldspathic rocks favoured strain localization and fault nucleation that controlled fold formation. The presence of pelitic layers within the thick-bedded quartzites had probably provided weakness zones that were more favourable for the strain localization than the previous foliation present in the quartzites. The quartzites and the quartzo-feldspathic rocks (granites and volcaniclastic rocks) accommodated heterogeneous high strain developing different degrees of mylonitization. The quartzites with protomylonitic textures are dominant and represent coarse-grained siliciclastic sediments that suffered metamorphism and partial dynamic recrystallization. Ultramylonites occur within discrete high-strain shear zones. It is probable that the strain localization in the PESZ involved both the effect of having layers of different competence and layers or stratigraphic contacts with rocks that experienced grain size reduction dominated by cataclasis and dislocation creep. Folds within quartzites with sub-horizontal to gently plunging hinges vary from closed to open in thick-bedded quartzites and from tight to closed in thin-bedded quartzites. Observed changes in structural style of deformed quartzites, slates and quartzo-feldspathic rocks are interpreted to result from the constraints imposed by the mechanical properties of the different lithologies. As the folds tightened during shortening, the alternating zones of contrasting competence favoured the disruption of the bedding. The deformation history in the PESZ was dominated by thrusting and strike-slip faulting along incompetent layers that locally developed staircase geometry and transected the lower Ordovician stratigraphic sequence. The kinematic model proposed for the PESZ is consistent with the models of transpressional shear zones stretched along strike with the development of coeval strike-slip and low angle oblique-slip faults associated to active buckle folds with axes parallel to the principal extension directio

Tectonothermal analysis of high-temperature mylonitization in the

Mylonites in pelitic and quartzofeldsphatic gneisses from the Ouguela tectonic unit (Coimbra–Córdoba shear zone, SW Iberian Massif) have been studied as an example of high-temperature ductile deformation associated with transcurrent tectonics. Detailed microstructural and P–T analysis indicates that ductile deformation evolved from a metamorphic peak at approximately 650–750 °C and 7.5–9.5 kbar (quartzofeldsphatic gneisses) and 730–790 °C and 7.5–9.5 kbar (pelitic gneisses) to retrograde conditions at 500–575 °C and 4.5/5.5–6.5/7.5 kbar (quartzofeldsphatic gneisses) and 525–600 °C and 3.5/4.5–5.5/7.5 kbar (pelitic gneisses). Following the metamorphic peak, exhumation was very fast. The P–T trajectory, which does not reach the curve for granite melting, is distinct that of isothermal decompression. Instead, the progressive and contemporaneous decrease in pressure and temperature was a direct response to strong heat dissipation along the contacts between the ascending slice and the adjacent blocks. The horizontal component of exhumation path, calculated for middle and shallower crustal levels, sum to ca. 57 km to 94 km (for the pressure peak). Assuming this offset acted in the Viséan during a time interval of ca. 9 Ma, the estimated exhumation horizontal slip rate is in the order of 6.3 to 10.4 mm/yr, which corresponds to an exhumation oblique-slip exhumation rate of 6.6 to 10.7 mm/yr (for ductile deformation). These values indicate that the transcurrent tectonic displacements accommodated by these mylonitic are similar to those of modern intra-continental shear zones, such as the still active Karakoram Fault (8.3 mm/yr) in the Himalayas. The Coimbra–Córdoba shear zone is therefore a typical intra-continental transcurrent zone with ten-to-one hundred kilometre along-strike mass movement of material that aided the exhumation of deep crustal rocks. Study of this large-scale structure in the SW Iberian Massif is therefore central to models of orogenic deformation during the amalgamation of Pangea

Superposition relations of microfabrics in the northern hanging-wall block

This study reports alternation of D2 extension-related and D3 contraction-related microfabrics in the northern hanging wall block of a gneiss dome-like structure recognized in the Évora Massif (Ossa-Morena Zone). In the Arraiolos – Santo Antonio de Alcorrego traverse high- to low-grade mylonites are dominant. Microfabrics related to D2 ductile deformation and M2 high-amphibolite to greenschist facies characterize an extensional shear zone with telescoping metamorphic isograds. D2 microstructures indicate shear sense with top-to-SE. Superposition of D3 contraction developed under greenschist facies (M3) producing folding of D2 microfabrics, mylonitization of granites along strike-slip shear zones and retrogression of M2 mineral assemblages

Zircon U–Pb geochronology of paragneisses and biotite

Sensitive high-resolution ion microprobe U–Th–Pb age determinations on detrital and inherited zircon from the E ´ vora Massif (SW Iberian Massif, Portugal) provide direct evidence for the provenance of the Ossa–Morena Ediacaran basins (Se´rie Negra) and a palaeogeographical link with the West African craton. Three samples of the Se´rie Negra paragneisses contain large components of Cryogenian and Ediacaran (c. 700–540 Ma) detrital zircon, but have a marked lack of zircon of Mesoproterozoic (c. 1.8–0.9 Ga) age. Older inherited zircons are of Palaeoproterozoic (c. 2.4–1.8 Ga) and Archaean (c. 3.5–2.5 Ga) age. The same age pattern is also found in the Arraiolos biotite granite, which was formed by partial melting of the Se´rie Negra and overlying Cambrian rocks. These results are consistent with substantial denudation of a continental region that supplied sediments to the Ediacaran Ossa–Morena basins during the final stages of the Cadomian–Avalonian orogeny (peri-Gondwanan margin with principal zircon-forming events at c. 575 Ma and c. 615 Ma). Combined with the detrital zircon ages reported for rocks of the same age from Portugal, Spain, Germany and Algeria, our data suggest that the sediment supply to the Ediacaran–Early Palaeozoic siliciclastic sequences preserved in all these peri- Gondwanan regions was similar. The lack of Grenvillian-aged (c. 1.1–0.9 Ga) zircon in the Ossa–Morena and Saxo-Thuringia Ediacaran sediments suggests that the sediment in these peri-Gondwanan basins was derived from the West African craton

Quality Assessment of Laser Welding Dual Phase Steels

Since non-conforming parts create waste for industry, generating undesirable costs, it is necessary to set up quality plans that not only guarantee product conformity but also cut the root causes of welding defects by developing the concept of quality at origin. Due to their increasing use in automotive industry, dual phase (DP) steels have been the chosen material for this study. A quality plan for welding DP steel components by laser was developed. This plan is divided into three parts: pre-welding, during and post-welding. A quality assessment regarding mechanical properties, such as hardness, microstructure and tensile strength, was also performed. It was revealed that DP steel does not present considerable weldability problems, except for the usual softening of the heat affected zone (HAZ) and the growth of martensite in the fusion zone (FZ), and the best analysis techniques to avoid failures in these steels are finite element method (FEM), visual techniques during welding procedure and digital image correlation (DIC) for post-weld analysis.The present work was done and funded under the scope of projects UIDB/00481/2020 and UIDP/00481/2020—FCT—Fundação para a Ciencia e a Tecnologia; and CENTRO-01-0145-FEDER- 022083—Centro Portugal Regional Operational Programme (Centro2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund. LAETA/INEGI/CETRIB is acknowledge due to the support provided in all research activities.info:eu-repo/semantics/publishedVersio