The study of the northern sectors of the Central Iberian autochthon allows a better understanding of the geodynamical evolution of the Iberian Variscides. During most of the lower Paleozoic a pervasive extensional episode could be put forward which should be related to the drifting of the Hun Super Terrane (Von Raumer et al., 2002) or Armorica plate (Matte, 1986) away from the Gondwana. Lithospheric anisotropies have played a major role during these times dominated by sedimentary processes. Concerning the upper Paleozoic times they have been dominated by the subduction/collision related to the closure of the Variscan oceans. The obliquity of this process induced in Iberia a sinistral transpressive regime (Dias and Ribeiro, 1995 and references herein). The existence of planar anisotropies formed, either during previous orogens or during the Variscan one, gives rise to a strong strain partitioning. This decoupling of the pure shear and simple shear components has been active since the early deformation events. Although it is possible to emphasize different tectonic stiles during most of the Devonian and Carboniferous, they could easily be explained by a progressive deformation, which is a better tectonic approach than the individualization of different Variscan tectonic events.
Besides the decoupling in the autochthonous that originated folds and coeval subparallel wrench faults, the decoupling processes should also have been active since the D1 in the parautochthon. In fact, whatever the root zone location in north Gondwana margin of the low grade Upper Parautochthonous structures, they must initially have been connected with the autochthon, at least in the initial stages of fold nucleation by buckling due to crustal shortening.
The D1 Variscan structures in the Upper Parautochthonous fold-nappes, preserved in the quartzitic levels of the Garraia - Santa Comba Arc, must represent the decoupling phase between the nappe and the underlying autochthon. Aerden and Malavieille (1999) for the large recumbent fold in low-grade Paleozoic metassediments of the Montagne Noire (SE of central Massif, France) proposed a model which include initial stages of homogeneous crustal thickening producing folds with steep axial planes that became rotated and amplified in a subhorizontal flow with pure shear and simple shear components related to low-angle thrusting. The continuation of the process led to a detachment of large fold-nappes by a basal thrust with low shear resistance from a continuous contracting footwall. The structural interpretation of the D1 structures in the Parautochthonous of Murça sector with a clear strain partitioning of pure shear component normal to the basal thrust plane and simple shear component parallel to it can be explained by spreading-gliding mechanisms of nappe formation and emplacement. The Palheiros – Vila Flor Thrust is here interpreted as the low shear resistance basal thrust.
In the continuation of nappe movement, the underlying autochthonous structures must have exerted a strong influence. All the kinematic indicators, both in D1, such as the ones associated with the mylonitic foliation, and in D2 simple shear dominated reactivation of previous planar structures and thrusts, indicate a top to ESE movement of the Upper Parautochthon nappe. In the Murça-Marão region, this movement direction is parallel, not only to the stretching lineation preserved in the autochthonous S1 cleavage but also to the regional D1 macrofolds and coeval parallel wrench faults. The close parallelism between the autochthonous and the parautochthonous structures could be explained if it is assumed that the major crustal discontinuities have worked like lateral ramps during the nappe emplacement; the observed displacement from WNW to ESE could than be the result of the Mondim-Murça–Moncorvo (Coke et al., 2000) and Malpica-Lamego (Dias, 1998; Llana-Fúnez and Marcos 1998, 2001; Coke et al., 2000) crustal shear zones. These are left lateral during D1 but eventually are reactivated as right lateral during D3 (Llana-Fúnez and Marcos 1998, 2001; Coke et al., 2000).
The arriving of the Upper Parautochthonous and above allochthonous pile must have induced the Main Trás-os-Montes Thrust layer parallel décollement and the above imbricated complex of Silurian Devonian forming the Lower Parautochthonous.