3D geometry, structure and formation of the Duero basin within the Pyrenean Orogen geodynamic scenario Geometría 3D, estructura y formación de la Cuenca del Duero en el contexto geodinámico del orógeno Pirenaico P. Granado 1 , O. Ferrer 1 , M. Butillé 1 , J. A. Muñoz 1 , E. Roca 1 , J.C. Ballesteros 2 , A. Giménez 2 , R. A.Vallejo 2 , , P. González 2 1 Geomodels Institut de Recerca, Departament de Geodinàmica i Geofísica, Facultat de Geologia, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, España. pablomartinez_granado@ub.edu 2 ENDESA Generación S.A., Subdirección I+D. C/ Ribera del Loira 60, Planta 0 E. 28042 Madrid, España Resumen: La Cuenca Cenozoica del Duero es una cuenca de antepaís que presenta una geometría de gran sinclinal formado por la flexión litosférica y la subducción de la corteza Ibérica bajo la corteza Cantábrico-Europea. La estructura interna de la cuenca está representada por fallas de alto ángulo que involucran a basamento y cobertera, sin haber generado grandes desplazamientos horizontales. El frente orogénico septentrional está representado por una serie de fallas dirigidas al sur que se enraizarían en la corteza inferior-media. Las relaciones tectónica-sedimentación muestran que las fallas del interior de la cuenca fueron activas durante el Cretácico superior-Paleoceno, previamente a la etapa de antepaís, mientras que el levantamiento del Orógeno y la actividad del frente de deformación se produjo durante el Eoceno-Oligoceno, localmente hasta el Mioceno. La Cuenca del Duero se comportó como un contrafuerte de escala orogénica al carecer de una arquitectura extensiva previa heredada del rifting Jurásico Superior - Cretácico Inferior asociado a la apertura del Golfo de Vizcaya. La contracción Alpina se focalizó allí donde la extensión Mesozoica fue más importante, como en el Margen Nor-Ibérico y el sistema de cuencas extensivas Mesozoicas del rift Pirenaico. Palabras clave: Cuenca del Duero; Subducción; Margen Nor-Ibérico; Extensión litosférica; Contracción continental. Abstract: The Duero foreland basin is characterized by a large synformal geometry formed by the lithospheric flexure and northward subduction of the Iberian crust underneath the Cantabrian-European crust. Basin structure is represented by high-angle faults that involve both basement and cover units, and that have not generated large amounts of horizontal displacement. The northern deformation front is represented by a series of south-directed faults that probably sole into middle-lower crustal levels. Growth strata within the basin interior indicate basement faulting occurred during the uppermost Cretaceous to Paleocene, previous to the onset of the foreland stage, while the Orogen uplift and the northern deformation front activity took place mainly between the Eocene-Oligocene, locally protracting until Miocene times. The Duero Basin behaved as an orogenic scale buttress due to the lack of an inherited Upper Jurassic. Early Cretaceous extensional architecture associated with the opening of the Bay of Biscay. Hence, most of the Alpine contraction had a major impact where Mesozoic extension was more important, like the North Iberian Margin and the system of Mesozoic extensional basins of the Pyrenean rift. Key words: Duero basin; Subduction; North Iberian Margin; Lithospheric extension; Continental contraction. INTRODUCTION The development of foreland basins is ultimately related to an orogenic system and associated tectonic forces that result in the bending of the lithosphere. The Cenozoic Duero basin is located in the north of the Iberian plate (Fig. 1) and developed during the collision between the Iberian and Eurasian plates. Deep geophysical imaging and modeling have demonstrated the northward down bending of the middle-lower Iberian crust underneath the Cantabrian-European one as a result of roughly N-S convergence (Fernández- Viejo, 1997; Gallastegui, 2000; Pedreira, 2004; Fig. 2). The geometry, internal structure and sedimentary fill of the Duero basin strongly differ to that of the easterly Ebro foreland basin. Such discrepancy is the ultimate consequence of the inherited architectural controls exerted by Late Jurassic to Early Cretaceous rifting that lead to the opening of the Bay of Biscay. Rifting related extreme extension was focused along the North Iberian Margin, where mantle and lower crustal rocks became exhumed (Roca et al., 2011), while progressive smaller amounts of extension took place eastward in the Basque-Cantabrian Basin and along the Pyrenean rift system. The Duero basin remained as an almost undisturbed 'cratonic' block where a series of