Cuantificación del acortamiento alpino y estructura en profundidad del extremo sur-occidental de la Cordillera Ibérica (sierras de Altomira y Bascuñana)

Abstract

In this paper we describe the structure of the SW border of the Iberian Range by means of the integration of structural, seismic and gravimetric data. These data allowed us to make two isobate maps, one relative to the top of the basement roof, and the other to the Upper Cretaceous limit, and six balanced cross-sections. The basement structure is mainly defined by normal faults that control the thickness of the Mesozoic units. We have distinguished three basement blocks limited by important fault zones: the Madrid Basin block, composed by granites and gneisses with a low fracture density, the Valdeolivas block, with Palaeozoic metamorphic rocks and a higher fracture density, and the Cuenca block, lithologically heterogeneous and with the highest fracture density. The MesozoicTertiary cover is detached from the basement dueto the presence of Upper Triassic plastic rocks. The main structures in the cover are thrusts and thrust-related folds bounded by transfer zones. The location of these two types of major structures is clearly related with basement normal faults. Shortening ranges calculated in the cover have a well-defined spatial distribution: maximum shortening (16 km) is located in the central sector of the Altomira Range, decreasing towards the north as far as compressive structures disappear. From the Tarancón fault zone to the south, N-S compressive structures soften and superimpose to the previous NW-SE ones.