Antón, Loreto

Gomes, António Alberto

Vegas, Ramon

Repositório Aberto da Universidade do Porto

Associação Portuguesa de Geomorfólogos Departamento de Geografia - FLUP, Via Panorâmica, S/N 4150-564 Porto Email: apgeom.dir@apgeom.pt     Título: 8º Congresso Nacional de Geomorfologia - Geomorfologia 2017 Editor: Associação Portuguesa de Geomorfólogos 8º Congresso Nacional de Geomorfologia - Geomorfologia 2017 Comissão Científica: Ana Paula Ribeiro Ramos Pereira, Carlos Valdir de Meneses Bateira, Diamantino Manuel Insua Pereira e Lúcio José Sobral da Cunha   Comissão Organizadora: Alberto Gomes, José Teixeira, Laura Soares, Jorge Trindade, Ricardo Garcia, Luca Dimuccio, Carlos Bateira, Claudia Manuel, Márcia Martins, Marta Araújo, António Silva e Eva Calicis Comissão Redactorial: António Alberto Gomes, José Teixeira e Laura Soares Fotografia de Capa: Frecha da Mizarela e vale do Caima, Arouca (José Teixeira, Outubro de 2017)  Capa: Claudia Manuel Composição e Edição: Claudia Manuel, Márcia Martins, Eva Calicis ISBN: 978-989-96462-7-8 Depósito Legal:  Porto, Outubro de 2017 Apoios: 7   8º Congresso Nacional de Geomorfologia 4-7 de Outubro de 2017 I Faculdade de Letras da Universidade do Porto Morphotectonic significance of the main lineaments in the Iberian Massif (Portugal and Spain)  Interpretação morfotécônica dos principais lineamen-tos no Maciço Ibérico (Portugal e Espanha)   R. Vegas1 *, L. Antón2, A. Gomes3 1 Dto. De geodinámica, Facitad de Ciencias geológicas. Universidad Complutense de Madrid. C/ Jose Antonio Nováis 4, 28040 Madrid, Spain. 2 Dpto. de Ciencias Analíticas, Facultad de Ciencias, Universidad Nacional de Educación a Distan-cia, Senda del Rey 9, 20840 Madrid, Spain. 3 Departamento de Geografia, Faculdade de Letras da Universidade do Porto- CEGOT, Porto, Portugal * ruidera@ucm.es Key-words: Add-ins, ArcGIS, Af, geomorphic indices, basin morphology, channel network Palavras-chave: Add-ins, ArcGIS, Af, índices geomórficos, morfologia da bacia, rede de canais  ABSTRACT   Lineaments are traditionally associated with analysis of aerial photographs and satellite and space images; although in their original definition they were merely considered as signifi-cant lines of landscape, caused by joints and faults which are observed mainly on topographic maps and less frequently in geo-logical ones (Hobs, 1904). In essence, they are surface features represented by alignments of ridges and furrows which are con-sidered to reveal the deep, subsurface, architecture of the rock basement (Antón, 2004). Tectonic characterization of topographic features has re-cently become a major concern due to the increased interest on neotectonics and sismotectonics. The observed lineaments – align-ments of geomorphic features such as hills, ravines and scarps – are considered here as surface expression of deep-seated features, following the general accepted consensus. They must represent a very complete image of the regional brittle tectonic fabric. With this perspective, we have generate a DEM map at scale 1:100.000 for the central-western Variscan (Iberian) Massif and extracted from it the main, apparent, lineaments. We have chosen this regional scale as the most appropriate for describing an enlarged regional brittle fabric of the western Iberian Variscan basement as well as for establish a tectonic-related frame for the main geomorphic features characterizing the area here studied (Vegas et al., 2012 ).  Three main sets of lineaments have been identified on the basis of their orientations and spatial linkages: a) NNE-SSW to NE-SW (N10-30° to N45°), b) ENE-WSE to E-W (N80° to N90°) and WNW-ESE (110°) and c) NNW-SSE (N130°- N140°) to N-S. They are conspicuous in all the area investigated but some of them do predominate in specific regions obscuring the occurrence of the others (Figure 1). With these premises, the lineaments of the Group a) are unequivocally related either to the N10° trending Vilariça and Regua-Verin faults or to the N45°-trending Plasencia (Messejana-Plasencia) Fault or Dike-fault System. These three faults have been described as transcurrent, left-handed strike-slip faults with small lateral movement with regard to its length, a maximum of 3 km lateral off-set for more than 500 km length in the Plasencia Fault. The lineaments of the Group b) – ENE-WSE to E-W (N80° to N90°) and WNW-ESE (110°) – correspond to thrusts and re-verse faults that cause, or are linked to, basement uplifts. This is the case of the Ponsul Fault and the lineament corresponding to Northern Border of the Central System. Thereafter, the slightly curved, festoon-like lineaments are here classified as thrusts that delimitate regularly highs and depressions in the topography. The lineaments of the Group c) – N130°-140° and N-S – show a much less influence in the topography. They contribute passively to the formation of the reliefs and must be correlated to previous faults (or brittle fabric) that does not take or take an insignificant part of the Cenozoic deformation. Within these lineaments one can mention the Porto-Tomar lineament guessed to be a Variscan first-order structure.  The overlook of an extensive area permits also the ascrip-tion of the main topographic features to the general frame drawn by the observed lineaments. In this sense, it is possible to estab-lish the interdependence between the overall attitudes of the main geomorphic units – i.e. the regional arrangement of the reliefs in the studied area – and the tectonic structures. This al-lows a first interpretation of the main geomorphic features in terms of the recent tectonic evolution resulted in the Paleogene and Neogene compressive events (N-S and NW-SW directed respectively, De Vicente and Vegas, 2009). Those main geomor-phic features correspond to (Figure 2):  · Two broad, relatively flat areas, the Northern and Southern Mesetas comprising the Variscan basement and its Ceno-zoic cover of the broad Duero and Madrid (Upper Tagus) basins. · Three E-W oriented swaths of basement uplifts that consti-tutes the main elevations of the western Iberian Peninsula, the Central System, most prominent relief – the main di-vide, the backbone of the early geographers – and the more modest ranges of the Montes de Toledo and the Sierra Morena Ranges in the Southern Meseta.  · Two NNE-SSW oriented, relatively narrow topographic Figure 1. Map of lineaments in the West-Central Hesperic Massif. Lines indicate fractures or faults with mainly transcurrent movement; barbed lines indicate thrusts. 8  R. Vegas, L. Antón, A. Gomes To these morphotectonic units, two basement elevations can be added: the Alentejo and Calatrava Swells that corre-spond clearly to the Neogene compressive event. The extraction of lineaments from a large-scale, 1:000.000, DEM map for the West-Central Variscan basement of the Iberian Peninsula has made possible the realization of a lineament map which provides a manageable method to link regional geomorphic features to intraplate tectonics. Also the lineament map brings a regional frame that enlarges the brittle tectonic fabric and serves to complete the mapped faults and fractures in the studied area. corridors composed of anastomosed, elongated ridges and basins, the Vilariça and Regua corridors. Their constrictive northern terminations constitute the reliefs of the NW Por-tugal-Leon ranges · Three Cenozoic basins in the interior of the Variscan base-ment of the southern Meseta,  Campo Arañuelo – between the Central System and the Montes de Toledo – Castelo Branco and Guadiana. Other minor basins in the Southern Meseta must be included in this type of features · Two open-to-the-sea Cenozoic basins, Lower Tagus and Sado Figure2. Major lineaments and morphotectonic units in the Iberian Massif. Thin lines indicate lineaments related to strike-slip fault and sheared zones; barbed lines correspond to thrust-related lineaments. Long fault corridors, PL: Plasencia-Messejana, M: Me-rida, E: El Escorial, R: Regua, V: Vilariça. Thrusts and ridges, AR: Ardila, CA: Caramulo,  B-A: Bejar-Avila,   E: Estrela,  G: Gardunha, GR:Gredos, G-RF: Gata-Sierra de Francia, G-S: Guadarrama-Somosierra, L: Lousã, M: Montanchez , P: Paramera, PO: Ponsul, SB: Southern Border (Central System),  SM: São Mamede, TM: Toledo Mountains VI: Villuercas. Cenozoic basins, C: Coria, CA: Campo Arañuelo, CB: Castelo Branco,  EB: East Badajoz, LM: La Mancha, S: Sado, WB: West Badajoz ACKNOWLEDGMENTS  This work was supported by UNED (GID2016-19); and it was partially funded by MITE (CGL2014-59516-P) and CARESOIL (S2013/MAE-2739) projects. GIS Technical support was funded under Grant PEJ-2014-A-93258.   REFERENCES  Antón, L., 2004. Análisis de la fracturación en un área granítica intraplaca: el Domo de Tormes. PhD Thesis, Universidad Complutense de Madrid, Madrid, 195 pp. De Vicente, G., Vegas, R., 2009. Large scale distributed deformation con-trolled topography along the western Africa-Eurasia limit; tectonic constraints. Tectonophysics, 474(1-2), 124-143. Hobbs, W.H. 1904. Elements of the Atlantic border region. Geological Socie-ty, American Bulletin, 15: 483-506. Vegas, R., Antón, L., Gomes, A., Medialdea, T., 2012 Lineaments in the West-Central Hesperic Massif (Portugal and Spain) and their geomorphic and tectonic significance. In: L.P. Fernández, A. Fernández,  A. Cuesta, J.R. Bahamonde (Eds.), Resúmenes extendidos del VIII Congreso Geológico de España. CD anexo Geo- Temas 13. Sociedad Geologica de España, pp. 1674-1677. Vegas, R., Antón, L., Gomes, A., Medialdea, T., 2012 Lineaments in the West-Central Hesperic Massif (Portugal and Spain) and their geomorphic and tectonic significance. In: L.P. Fernández, A. Fernández,  Cuesta, J.R. Bahamonde (Eds.), Resúmenes extendidos del VIII Congreso Geológico de España. CD anexo Geo- Temas 13. Sociedad Geologica de España, pp. 1674-1677. 

Morphotectonic significance of the main lineaments in the Iberian Massif (Portugal and Spain)

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Morphotectonic significance of the main lineaments in the Iberian Massif (Portugal and Spain)

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