Superposed buckle folding in the eastern Iberian Chain, Spain

Abstract

The Aliaga area (eastern Iberian Chain) shows large-scale examples of buckle superposition developed during Tertiary folding. In most cases, ENE-trending folds overprint earlier NNW–SSE-trending ones. The resulting structures are mapped, analysed, and genetically classified by comparison with analogue models described by several authors. The following types are found: standard Type 1 (1a: dome-and-basin structure, 1b: unequal-wavelength overprinted folds); modified Type 1 (1c: T-shaped ‘joined’ folds; 1d: T-shaped ‘abutting’ folds; 1e: L-shaped folds; 1f: ‘snake-like’ folds); standard Type 2 (2a: non-cylindrical buckling of earlier axial surfaces involving hinge replacement). Different superposed sets of flexural-slip striations record successive folding episodes in snake-like folds, and hinge replacement in the case of Type 2a superpositions. Types 1 and 2 apparently develop where the earlier folds have interlimb angles over and below 90°, respectively, which fits the results of analogue modelling and theoretical analysis by previous authors. Types 1b and 1d are associated with higher W1/W2 wavelength ratios than Types 1a and 1c. Other controlling factors are viscosity contrast and erosion processes. Specifically, erosion of competent limestone beds in the hinge zone of a NNW–SSE-trending anticline allowed the near-vertical eastern limb to be refolded into snake-like folds.