La prolongación del Despegue de Salamanca (segunda fase de deformación varisca) en el Horst de Mirueña (Zona Centro Ibérica)

Abstract

The studied area is included into the Central Iberian Zone (C.I.Z.), an internal zone of the Variscan orogen characterized by its stratigraphy consisting of thick pre-Ordovician terrigenous sequences and by the transgressive character of the Lower Ordovician. From a morphological point of view is known as the Mirueña Horst, upraised in alpine times. Metasediments and variscan granites are quite distinctive lithologies in this area. The oldest sedimentary rocks outcropping in the area are considered to be of Late Vendian age and are overlain by an uncomfortable Lower Ordovician. Structuraly speaking it is settled in the South Domain of the C.I.Z., the so called Domain of Vertical Folds, characterized by a first compressional event, D1, wich gave rise to steep folds trending NW-SE and a subvertical foliation, S1. During the first deformation a pro grade metamorfic evolution of intermediate pressure type is evidenced by the growth of chlorite, biotite, almandine, staurotide, kyanite and sillimanite. The second event D1 gave rise to the development of a subhorizontal penetrative foliation as well as to minor folds and asymmetrical structures indicatives of non coaxial deformation. Pre D1 granites were myloniticed and syn-D2 granites were heterogeneously deformed. D2 structures are there related to a ductile shear zone of extensional character, more than 2 km wide that displaced the hangingwall unit to the SE. Quartz e-axis fabrics and kinematic criteria are indicative of simple shear componets. However, coaxial components were probably also involved. The extensional character of the ductile shear zone is indicated by the thinning of the metamorphic zones, with the dissapearance of part of the almandone zone, and by the metamorphic evolution. We postulate that the area studied might be related to the prolongation of a very important extensional ductile shear zone described to the west : the Salamanca Detachment Zone. The extension direction was pararell to the trend of the belt. This feature is characteristic of syn-orogenic collapse in other orogens.