Rodriguez, J., Coke, C., Dias, R., Pereira, E. and Ribeiro, A. 2005.   Transition from autochthonous to parautochthonous deformation regimes in Murça-Marão sector (Central-Iberian Zone, northern Portugal). In: (Eds.) Rodolfo Carosi, R Dias, David Iacopini, and Gideon Rosenbaum, The southern Variscan belt, Journal of the Virtual Explorer, Electronic Edition, ISSN 1441-8142, volume 19, paper 8, doi:10.3809/jvirtex.2005.00124

Transition from autochthonous to parautochthonous deformation regimes in Murça-Marão sector (Central-Iberian Zone, northern Portugal)

J. Rodriguez

Instituto Nacional de Engenharia Tecnologia e Inovação, Departamento de Geologia, Rua da Amieira, 4466-956 S. Mamede de Infesta, Portugal

C. Coke

Dep. Geologia, Univ. Trás-os-Montes e Alto Douro and LATTEX Portugal.

R. Dias

Dep. Geociências, LIRIO and Centro de Geofísica, Univ. Évora, Convento das Maltezas, 7100-513 Estremoz, Portugal.

E. Pereira

Instituto Nacional de Engenharia Tecnologia e Inovação, Departamento de Geologia, Rua da Amieira, 4466-956 S. Mamede de Infesta, Portugal

A. Ribeiro

Dep. Geologia and LATTEX, Univ. Lisboa, Edifício C2, Piso 5, Campo Grande, 1700 Lisboa, Portugal.

Abstract

A comparison is made between the structures induced by the main variscan deformation tectonic event (D1) in the Autochthon of Central-Iberian Zone (northern Portugal) and in the overlying lower unit of the nappe pile complex of NW Iberia; due to the close lithostratigraphic similarities between both units, the lower allochthonous complex is considered as a Parautochthonous unit

In the Autochthon the D1 tectonic event have produced folds in a transpressive regime where a strong heterogeneous partitioning between the pure and the simple shear components could be emphasize. The amount of partitioning was influenced by the proximity, either to deep structures in the pre-variscan basement or to major sin-kinematic faults.

Concerning the Parautochthonous, several features have controlled the geometry and kinematic of the D1 variscan structures:

  • the existence of stratigraphic levels with specific rheologies (e.g. the Silurian black shales);

  • the obliquity between the transport direction of the thrust nappes and the autochthonous structures;

  • the steepness of the D1 macrofolds in the Autochthon.

The discussion of the distinct behavior of D1 variscan structures in both units allows a better understanding of the geodynamical evolution of the NW Iberian nappe complex. In the proposed model, the upper part of the Parautochthon (with a fold nappe style) was emplaced by a spreading-gliding mechanism, while in the lower part (consisting of an imbricated thrust system) a push-from-the rear mechanism predominates.

Keywords: Variscan, Autochthon, Parautochthon, Nappe emplacement, Transpression, Fold nappe Iberia, Portugal