Special Issue Article
Folding in orogens: a case study in the northern Iberian Variscan Belt
Article first published online: 19 JAN 2010
Copyright © 2010 John Wiley & Sons, Ltd.
Special Issue: Structural analysis of fold-and-thrust belts
Volume 45, Issue 5-6, pages 597–622, September - December 2010
How to Cite
Bastida, F., Aller, J., Pulgar, J. A., Toimil, N. C., Fernández, F. J., Bobillo-Ares, N. C. and Menéndez, C. O. (2010), Folding in orogens: a case study in the northern Iberian Variscan Belt. Geol. J., 45: 597–622. doi: 10.1002/gj.1199
- Issue published online: 1 SEP 2010
- Article first published online: 19 JAN 2010
- Manuscript Accepted: 6 OCT 2009
- Manuscript Received: 27 MAR 2009
- structural analysis;
- shear zones;
- Variscan Belt;
Folding during the Variscan deformation in NW Iberia has been analysed from the foreland to the hinterland of the orogen using several geometrical techniques complemented by the numerical simulation of kinematical folding mechanisms with the aid of a computer program (‘FoldModeler’). In the foreland, folds are related to thrusts; in the inner zones, folds can be attributed to three deformation phases. D1 and D2 involved deformation with horizontal foreland-directed displacements. D1 gave rise to closed or tight folds (F1) and cleavage (S1); development of large recumbent F1 folds in the hinterland required a simple shear regime and a final coaxial strain component with sub-vertical maximum shortening. Strain incompatibilities at deeper levels, together with high temperatures, favoured the concentration of ductile deformation in shear zones and development of mylonites during D2. Local flow instabilities generated F2 folds that were passively amplified by a combination of simple shear, coaxial strain and area change. D3 involved a change to a regime with dominant coaxial deformation and a sub-horizontal maximum shortening; it gave rise to upright or steeply inclined folds (F3). Development of D3 structures was heterogeneous and depended on the previous dip of the bedding and S1, the presence or emplacement of granitoids, the stacking of thrust sheets or the previous development of large faults bringing into contact rocks with different competence. D3 structures are mainly concentrated in metapelitic areas and appear distributed in bands on several scales. On a small scale, tectonic banding appears associated with small folds as a result of pressure-solution processes. In areas with sub-vertical S1, later sub-horizontal kink bands were formed by a vertical compression. Copyright © 2010 John Wiley & Sons, Ltd.