Dating folding beyond folding, from layer-parallel shortening to fold tightening, using mesostructures: Lessons from the Apennines, Pyrenees and Rocky Mountains

Abstract

Abstract. Dating syntectonic sedimentary sequences is often seen as the unique way to constrain the initiation, kinematics and rate of folding and the sequence of deformation in the shallow crust. Beyond fold growth however, deformation mesostructures accommodate the internal shortening of pre-folding strata before, during and after strata tilting. Absolute dating of mesostructures developed during extension at fold hinge may help constrain the duration of fold growth in the absence of preserved growth strata, while dating of mesostructures related to layer-parallel shortening and late fold tightening provide a valuable access to the timing and duration of the entire folding event. We compile existing ages in the literature and provide new U-Pb ages of calcite cements from veins and faults from four folds (Apennines, Pyrenees, Rocky Mountains). Our results not only better constrain the timing of fold growth but also reveal a contraction preceding and following folding, the duration of which might be function of the tectonic style and regional sequence of deformation. This study paves the way for a better appraisal of folding lifetime and processes and of stress evolution in folded domains.\n