Orogenic reworking and reactivation in Central Iberia: A record of Variscan, Permian and Alpine tectonics

Abstract

[EN]Interference between orogenic systems and deformation phases within them may lead to reworking and reactivation of previous structures. The eastern sector of the Spanish-Portuguese Central System holds evidence of two orogenic systems, Variscan and Alpine, plus a stage of Permian extension. We perform an integrated structural analysis to identify reworking and reactivation processes throughout the geological record. The Variscan record starts with crustal thickening (D1; E-verging overturned folds). A second phase features the intraorogenic collapse of an overthickened crust (D2; top-to-the-SE ductile extensional shear zone), which produced intense structural reworking at the core of the shear zone and moderate reworking at its hanging wall. During subsequent strike-slip tectonics, crustal thickening parted transpressional deformation into a dextral shear zone and upright folds (D3). Variscan deformation did not reactivate previous structures, but exploited a weak rheological boundary defined by contrasted lithologies (sedimentary versus igneous rocks) to accommodate D2 shearing. Reactivation played a role afterwards: Variscan strike-slip shear zone acted as a transfer fault to accommodate Permian extension (post-orogenic collapse), and then Alpine contraction. The Permian extension record is blurred by Alpine inversion, although the trend of Alpine structures in Central Iberia, and the Spanish- Portuguese Central System, may result from Permian structural inheritance.