Hercynian transpressional tectonics at the southern margin of the central Iberian zone, western Spain

McGowan, James Andrew (1991) Hercynian transpressional tectonics at the southern margin of the central Iberian zone, western Spain. University of Southampton, Doctoral Thesis.

Abstract

The La Codosera area is located within the Central Iberian Zone just to the north of the Badajoz-Cordoba shear zone. In this area, resting unconformably on Precambrian schists and greywackes, are three ridges (the Southern, Central and San Pedro ridges) of Palaeozoic slates and quartzites. These rocks have been affected by Hercynian ductile deformation and late brittle faulting and kinking which intensifies towards the Badajoz-Cordoba shear zone producing a marked variation in structural style from fold/thrust to strike-slip tectonics. Hercynian deformation produced 3 early fold phases. On the Southern Ridge F1 folds are tight, asymmetric and face upwards. F2 folding becomes locally intense, fold limbs are sheared and extended and the folds record a sinistral vergence. Small scale N/S trending F3 folds occur locally. Strike-parallel faults dip steeply and record oblique/strike-slip sinistral movement. Bedding is cut at a high angle by these faults which define an asymmetric flower structure which verges to the north tectonically thickening the succession. Kinematic indicators (composite planar fabrics, rotated and shear folds, asymmetric porphyroclasts, asymmetric boudinage) are abundant and indicate left-lateral strike-slip shear. Northwards there is a marked decrease in the shear component of the deformation. Within the Central Ridge F1 folds are cross-cut by thrusts whilst F2 and F3 folds are rare. The thrusts repeat stratigraphy but record some oblique sinistral shear. Farther north, within the San Pedro Ridge, no strike-slip structures are observed; folds and thrusts dominate. Within the Precambrian, north of the San Pedro Ridge, a deformation phase prior to the Hercynian is recorded. This produced upright, open folds, faults and veins but no cleavage. Hercynian deformation overprints these structures producing a penetrative S1 cleavage which transects the pre-Hercynian folds. This generates a variable plunging Ss/S1 intersection lineation and variable facing relationships.

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