Quantifying deformation processes in the SE Pyrenees using U–Pb dating of fracture-filling calcites

Abstract

It is difficult to quantify the timing of the deformation processes in brittle fold–thrust belts because minerals suitable for dating and well-preserved growth strata sediments are scarce or absent. Here, we quantify the duration of thrust sheet emplacement and shortening rates in the SE Pyrenean thrust sequence using U–Pb dating of fracture-filling calcites. The obtained U–Pb dates reveal a minimum duration for the emplacement of each thrust unit (18.7 Ma for the Bóixols–Upper Pedraforca, 11.6 Ma for the Lower Pedraforca and 14.3 Ma for the Cadí thrust sheets) and show that piggy-back thrusting was accompanied by post-emplacement deformation of the upper thrust sheets above the lower sheets during their south-directed tectonic transport. We calculated shortening rates of 0.6, 3.1 and 1.1 mm a −1 from the older to younger emplaced thrust sheets. Our results also reveal the formation of local normal faults during the late Oligocene as a result of the late stages of compression and exhumation in the SE Pyrenees. We observed that temperatures >110 °C could be a limiting factor when applying the U–Pb dating method. Supplementary material: U-Pb analytical results, concordia plots and fracture data are available at https://doi.org/10.6084/m9.figshare.c.5078862