Variscan suporposition on Ordovician extensional fault-related folds in the Eastern Pyrenees

Abstract

Our study investigates pre-Variscan Ordovician tectonics in the La Molina area (Eastern Pyrenees, Spain) by means of geological mapping and structural analysis of mesostructural data. We revisit the structural interpretation of pre-Upper Ordovician folds, revealing two mutually orthogonal, cleavage-free fold systems (WNW–ESE and NNE–SSW striking) affecting the Late Cambrian to Early Ordovician Serdinya Formation. These folds are interpreted as fault-related folds formed above steeply-dipping extensional faults during Mid Ordovician rifting. The geometry and orientation of Variscan mesostructures are shown to be strongly influenced by these earlier Ordovician folds, explaining the wide dispersion of fold axes and cleavage-bedding intersection lineations only found below the Upper Ordovician unconformity. The Upper Ordovician unconformity seals and locally erodes the limbs of those pre-existing folds. The hectometric to kilometric scale cleavage-free Ordovician folds contrast with the finer smaller-scale Variscan syn-foliar folds, and thus explains the absence of fold interference patterns. This work highlight that collecting and analysing detailed mesostructural data in orogenic hinterlands remains essential for interpreting regional tectonics, and it advances our understanding of the early tectonic evolution of the northern Gondwana margin.