Structural zonation as a result of inhomogeneous non-coaxial deformation and its control on syntectonic intrusions: an example from the Cap de Creus area, eastern-Pyrenees

The Hercynian structure in the Pyrenees is characterized by the overprinting of several deformational events, each one associated with spatial changes in tectonic style. The variations in tectonic style depend on the lithological setting and on the tectonic regime, both changing in space and time. However, structural zonations also arise from inhomogeneity of deformation during one event. The studied area in the Cap de Creus is an example of the transition from low strain domains, where an earlier foliation is slightly folded, to a high strain domain, where tight or isoclinal folding caused the transposition of the earlier foliation. This structural inhomogeneity was developed from progressive deformation involving the generation of minor S-shaped folds and a major shear zone-like structure consisting on an open Z-bend. Both structures display steeply plunging axes. Initial flexural flow folding followed by limb stretching and shearing of the major structure is invoked to explain apparently contradictory symmetries and shear senses. This folding event, and the associated strain distribution, controlled the emplacement of a syntectonic pegmatite dike swarm. Dikes occur preferentially within the high strain domain, and are either boudinaged or folded depending on their orientation. A late system of narrow ductile shear zones overprint all earlier structures. © 1994.