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Brilha et al_2005

Francisco Sousa

Published on July 20, 2014

–Geology and metallogenesis of the Iberian Pyrite Belt; –The Iberian W-Sn Metallogenic Province; –The Silurian of the Portuguese Ossa Morena Zone; –Meso-Cenozoic of the Algarve; –Low coasts of Portugal; –River network, rañas and Appalachian-type landscapes of the Hesperic massif; –Tertiary basins of the western Iberian margin; –Jurassic record in the Lusitanian Basin; –Dinosaurs of western Iberia; –Ordovician fossils from Valongo Anticline; –Karst systems of Portugal; –South Portuguese Palaeozoic Marbles; –The Azores Archipelago in the America-Eurasia-Africa triple junction; This paper is therefore the result of all contributions and sugges- tions. New well-justified proposals will be considered in a future revi- sion of this work. The next immediate step will be the nomination of the most relevant geosites representative of each framework, based on an accurate identification, characterisation and quantification. These geosites will constitute the most remarkable elements of geological heritage in Portuguese territory. Therefore, they must be given a high priority in any implementation of geoconservation strategies. The fourteen frameworks are presented according to their geo- graphical relevance illustrating the high geodiversity level in Portu- gal (Figure 1). The description of each category is not exhaustive and just the most relevant scientific settings are presented. A geotraverse through the Variscan Fold Belt in Portugal (by A. Ribeiro) The backbone of the Iberian Peninsula is formed by basement rocks that are part of the Variscan Fold Belt. This Belt extends from Cen- tral Europe to Western Europe and Morocco delineating a series of arcuate mountains. This belt was generated by the opening and clo- sure of oceans of variable size between the upper Proterozoic (~540 Ma) and the upper Paleozoic (~250 Ma). The best traverse across this Variscan Fold Belt is in the Iberian Peninsula because: i) the transverse is the most complete, foreland (Cantabrian Zone around Oviedo in NE Spain) to foreland (South Por- tuguese Zone in SW Portugal), and ii) the basement is exposed continu- ously if we avoid the Meso-Cenozoic basins in its borders and the dis- continuous Cenozoic basins in the center of Iberia. Therefore, its pristine geological features are preserved from more recent events related to the opening of the Atlantic and closure of Tethys (Ribeiro et al., 1991). Finally, the climatic conditions and vertical movements provide beautiful exposures of rocks and structures in coastal cliffs, deep rivers and elevated mountains. In fact, some of the most significant exposures of the Belt are located at different spots in Iberia. They contribute to a deeper understanding of the processes that shaped the belt and its extension downwards to deeper crustal levels. Geology and metallogenesis of Iberian Pyrite Belt (by F.J.A.S. Barriga, J.M.R.S. Relvas, J.M.X. Matos) The Iberian Pyrite Belt (IPB) contains a colossal amount of vol- canic-hosted massive sulphides, with a pre-mining total of more than 1750 Mt containing 22 Mt Cu, 34 Mt Zn and 12 Mt Pb, respectively. This is comparable only, on a worldwide basis, to the Urals Belt of Russia. However, while the Urals Belt extends for nearly 2500 km, the IPB is only about 250 km long. Thus, the concentration of sulphide ores is an order of magnitude greater in the IPB. The IPB has been mined continuously since the Chalcolithic era. The Rio Tinto deposits of Spain, the first to gain world fame, are considered the largest of their class ever to form, with over 500 Mt of sulphide ores. The Aljustrel and Neves Corvo deposits (Portugal) are among the world’s richest deposits of their class in Zn and Cu (>8Mt and >4Mt, respectively). Additionally, Neves Corvo’s copper and tin ores depict the highest grades recorded for deposits of their class (e.g. Carvalho et al., 1999; Relvas et al., 2002). The deposits are hosted by a well-preserved volcanic-sedi- mentary complex, in a tectonic setting interpreted to represent continental fragments that collided obliquely during the Variscan orogeny, following subduction of an oceanic realm. The tectonic evolution produced thrusting and formation of pull-apart basins, which host the deposits (see Tornos et al., 2002). The post-depo- sitional history of the deposits is well recorded. All geological and metallogenetic aspects of the IPB are well studied and many constitute classic studies in the literature. Detrital and chemical sedimentation, volcaniclastic deposition, hydrothermal activity and mineralization, syn-sedimentary and transpressive deformation are all clearly visible. Additionally, the IPB is studied also through detailed comparisons with present- day submarine hydrothermal sites, including examples not only in the Atlantic but also in the Pacific (e.g. Pacmanus in Papua New Guinea). The IPB is still an actively studied geological object. Among the main aspects being researched, we can men- tion sedimentation and its role with respect to mineralization, submarine physical volcanology, the position of mineralization Episodes, Vol.28, no.3September 2005 178 Figure 1 Geological map of Portugal.