Partitioned tectonic shortening, with emphasis on outcrop-scale folding and flattening, Pindos fold-and-thrust belt, Peloponnese, Greece

Abstract

Shortening estimates for fold–thrust belts seldom take into consideration outcrop-scale folding, especially folding related to prethrusting layer-parallel shortening (LPS) and flattening. The Pindos belt of the Peloponnese contains products of Maastrichtian to Paleocene tectonic shortening amenable to assessing strain partitioning. Shortening there initiated with LPS, including outcrop-scale folding, which was superseded by thrusting and macrofolding, with both macromechanisms producing additional outcrop-scale folding and (or) form-modification of initial LPS outcrop-scale folds. Skourlis and Doutsos (2003. International Journal of Earth Sciences, 92: 891–903) concluded that total shortening in this region was 68%, the summation of ∼15% LPS, ∼6% fault-related macrofolding, and ∼47% thrust–slip translation. But even this degree of shortening may be underestimated when outcrop-scale folding is considered. Two limestone-dominated Cretaceous formations and one Cretaceous–Eocene formation of limestone and mudstone display spectacular outcrop-scale folding produced by true multilayer behavior, internal buckling, and disharmonic quasi-flexural folding. Fold forms vary from chevron buckling of multilayers to more rounded folding of true multilayers to disharmonic flattened folds in pseudo-bedded limestone. Ramsay analysis of layer thickness variations across individual disharmonic folds underscores the disharmonic fold forms and intense degree of pressure dissolution generated fold flattening. Line-length shortening for well exposed “packages” of LPS outcrop-scale folding is as high as 30%, but overlying and underlying panels may be more modestly folded and (or) flattened, suggesting that shortening transfer mechanisms may have caused some sections to be bypassed. Achieving more meaningful shortening estimates of the outcrop-scale folding within an entire progressive deformation will require understanding of the partitioning of distribution of this folding regionally.