Intraplate deformation in the NW Iberian Chain: Mesozoic extension and Tertiary contractional inversion

Abstract

The Iberian Chain developed within the Iberian plate during the Palaeogene and Early Miocene as a result of convergence between the African and Eurasian plates. It is a fold-and-thrust belt, which involves the Hercynian basement and the Mesozoic and Cenozoic cover. A generalized cross-section of the NW part of the Chain, of 195 km length, is presented. Mesozoic basins, developed on the Hercynian basement, display thickness variations across normal faults that bounded them and that can be recognized in the field. The Tertiary contraction deformed and inverted the Mesozoic basins, and it is inferred to have produced a thrust sheet about 5 km thick in its frontal (northeastern) part, which thickens to the SW. The total Tertiary shortening in the section is 66.6 km (26%). The structure and the crustal shortening and thickening of the Iberian Chain are explained by a major upper-crustal thrust system with simple flat-and-ramp geometry, which may branch to the Pyrenees or the Betics. This is combined with internal deformation of the thrust sheet. The contribution of the Iberian Chain shortening to the convergence of the African and Eurasian plates during the Tertiary is about one-half of that of the Pyrenees, and should be taken into account in any reconstruction of the kinematics of these plates.