The role of tectonic inheritance in the development of recent fracture systems, Duero Basin, Spain

Abstract

A lineament analysis of the Duero Basin (north Spain) suggests that cover rocks have been influenced by a previously fractured basement in sediment cover with little deformation. The Duero Basin is covered with horizontal Neogene rocks (mainly sandstones, shales and limestones) with a total outcropping area of about 50 000 km² and a maximum thickness of 300 m. The only structures found within the Neogene are map-scale monoclines near the basin margins, and joints and faults, most of them without significant displacement. From the analysis of a Landsat Thematic Mapper (TM) scene, lineaments were mapped at the eastern half of the Duero Basin. The orientation frequency of lineaments shows an absolute maximum NE–SW to ENE–WSW, with several sub-maxima oriented E–W, NW–SE and WNW–ESE. These fracture directions controlled most of the present-day fluvial network. Within the Palaeozoic and Mesozoic rocks cropping out at the basin margins the orientation of lineaments corresponds with that of mappable faults, particularly in the Palaeozoic basement. The zones with maximum density of lineaments are associated with map-scale WNW–ESE thrusts and folds located below the horizontal Neogene. The origin of the main fracture systems in the Neogene rocks of the Duero Basin appears to be controlled by older structures, namely the NE–SW faults that cross-cut the granitic and gneissic basement of the Duero Basin and its southern and western margins. These faults are late Variscan (probably Permian) in origin and were reactivated during the Mesozoic and the Cenozoic. Their activity in Miocene and post-Miocene times is related to strike-slip and extensional movements linked to the recent intraplate stress field in the Iberian Peninsula.

Acknowledgments

The authors are grateful to M. J. Marín and M. P. Sancho (Centro de Tratamiento de Imágenes de la Universidad de Zaragoza), who developed the lineament analysis program used in this study, and to Dr Javier Bernal (CAMD-NIST, USA), who developed the TRIANGLE program for the application of Delaunay method. The comments and suggestions of A. Tremblay, A. Vauchez, E. de Kempt and E. M. Schetselaar contributed significantly to improve this paper. This work was financed by projects PB97-0997 of the Dirección General de Enseñanza Superior (Spain) and 221-98 of the University of Zaragoza.