Geometry and regional significance of neoproterozoic (Cadomian) structures of the Narcea Antiform, NW Spain

摘要

The Narcea Antiform is located at the hinterland-to-foreland transition of the Variscan belt in the NW of the Iberian massif. It consists of an antiformal stack of fault-propagation folds that developed in the hanging wall of allochthonous thrust sheets during the first Variscan deformation event in the Palaeozoic rocks. The Neoproterozoic Narcea Slates Formation, cropping out in the core of the Narcea Antiform, records a Cadomian deformation event that formed large asymmetric NW-vergent folds, with related axial planar cleavage, developed in the lower greenschist facies. These folds are truncated by the Lower Cambrian angular unconformity. Lower Cambrian conglomerates contain pebbles with predepositional microstructures that are widespread in the underlying Neoproterozoic rocks. The Narcea Antiform provides valuable information concerning major tectonic Cadomian events. The large-scale, near-recumbent Cadomian folds developed between 560 and 540 Ma. Top-to-the-NW kinematics can be deduced for the Cadomian plate convergence (transverse to the Variscan convergence) in present coordinates. It was followed shortly afterwards by large displacements along the northern Gondwana margin that resulted in its accretion alongside the essentially undeformed Neoproterozoic rocks of the Central Iberian Zone before Early Cambrian times.