Estudio de fábricas magnéticas y su relación con la deformación en el sector centro-occidental del Pirineo central (Aragón y Navarra)

Abstract

Abstract: In this work a magnetic fabric analysis (indirect measurement of the magnetic mineral orientation) and its relation with the strain is developed along the southern Pyrenean and Northern Ebro Foreland basins. The obtained results permit to identify the presence of a tectonic imprint in the magnetic fabrics related to a horizontal layer parallel shortening process developed at pre-tilting conditions, a competence between previous fabrics and other tectonic processes related to the cleavage development and the imprint of a regional shear process identified at the inner zones of the chain. These fabrics at the syn-tectonic deposits exhibit a very early record of the strain processes with magnetic patterns developed near to the emplacement conditions of gravitational structures (slumps) and without significative modifications during later processes. These later processes can comprise the diagenetic flattening related to the vertical loading or the tectonic shortening related to folds and cleavage development. The detailed study of these fabrics shows a high record sensibility of shortening processes at low deformation domains (as can be identified in foreland basin settings at tens of kilometers to the South of any macroscopic evidence of deformation) and a non straightforward cleavage affection identification in the cleaved domain. In this setting a competence between bedding related fabrics (vertical loading and horizontal tectonic shortening) and the cleavage plane is identified. This competence is observed through a magnetic lineation parallel to the intersection lineation between bedding and cleavage planes, small data girdles and though small anisotropies of the confidence zones of the magnetic axes. This aspect means an apparent change of the strain record at the AMS and where the cleavage deformation is, in many cases, non evident. This competence is identified along the whole cleavage domain and permits to constrain a similar strain sensibility of AMS to this process, while its identification can comprise a more detailed data analysis. These magnetic fabric changes are identified with independence of the mineralogical variations at basin scale. Such changes are mainly related to the sedimentary and early diagenetic conditions of the sedimentary bodies. On the other hand, the ferromagnetic contribution to the susceptibility shows a tectonic control in the appearing of the regional macroscopic Pyrenean cleavage that can show increases in a logarithmic manner.