Abstract

The Madrid basin is intracratonic and triangular in form, being bounded on its three sides by Tertiary mountain ranges: the Spanish Central System in the north, the Toledo mountains in the south, and the Iberian and Altomira ranges in the east. The Altomira range separates the Loranca basin from the Madrid basin (Fig. 1). Each of these mountain ranges has a different structure and Tertiary geological evolution. The kinematic history of each of these borders of the Madrid basin reflects differences in the transmission of stresses from the active Iberian plate boundaries where the Betic and Pyrenean chains themselves had distinctive kinematic histories.

Geological setting

The crust of the Madrid basin and its surroundings is characterised by: 1. a Variscan basement (Palaeozoic metamorphic rocks with granitoids); 2. a pre-tectonic cover of Mesozoic and Early Cenozoic age (the former thinning gradually and then disappearing westwards); and 3. a syn-to post-tectonic cover of alluvial, fluvial and lacustrine sediments of Late Oligocene to Late Miocene age.

The structure of the borders of the Madrid Basin

Spanish Central System (SCS)

This is a linear mountain range that trends ENE–WSW, forming the Guardarrama Mountains, and then changes to trend E–W in the west, where it forms the Gredos Mountains. The altitude of the range is commonly 1500 m higher than the surface of the Madrid basin. The basement forms a core, flanked by the pretectonic cover.