Paleostress evolution in the South Pyrenean fold and thrust belt based on the structural analysis of fractures and U-Pb dating of carbonates

Structural analyses of vein and faults related with the growth of the South Pyrenean fold and thrust belt are coupled with the U-Pb ages of fracture-filling calcites compiled in Cruset et al. (2020) and Muñoz-López et al. (2022). Fractures include conjugated vein systems and reverse, strike-slip and normal faults cemented by calcite. The results reveal the orientation of tectonic stresses during the Pyrenean compression and their spatial and temporal evolution since the Late Cretaceous.

 Late Cretaceous to late Palaeocene U-Pb dates between 70.6 and 55.3 Ma registered compressional deformation in the inverted Mesozoic salt-related extensional basins corresponding to the Bóixols and Upper Pedraforca thrust sheets. Calculated paleostresses show a predominant N-S direction of tectonic transport, with more pronounced NW-SE directions in the western termination of the Bóixols and in the northern sector of the Upper Pedraforca.

Fracture data and U-Pb ages between 47.9 and 42.3 Ma measured in the Lower Pedraforca thrust sheet reveal N-S and NW-SE directions of tectonic transport during the middle Eocene, similar to those in the Bóixols and Upper Pedraforca thrust units. Contrarily, younger late Eocene to Oligocene U-Pb ages between 36.2 and 28.4 Ma measured in the lowermost Cadí thrust sheet reveal an homogeneous N-S trend during the emplacement of this unit.

Fractures cutting the Bóixols and Upper Pedraforca thrust sheets, and filled with cements yielding U-Pb ages from 48.8 to 25.68 Ma, show the same directions of tectonic transport than those measured for the Late Cretaceous-Paleocene. These Eocene and Oligocene ages also register the post-emplacement deformation of upper tectonic units on top of the Lower Pedraforca, Cadí, Montsec and Serres Marginals lower thrust sheets.

This research was funded by the project ALORBE (PIE-CSIC-202030E310), DGICYT Spanish Projects PID2021-122467NB-C22 and PGC2018-093903-B-C22 Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación/Fondo Europeo de Desarrollo Regional, Unión Europea. David Cruset acknowledges the Spanish Ministry of Science and Innovation for the "Juan de la Cierva Formación” contract FJC2020-043488-I AEI/10.13039/501100011033.

References

Cruset, D. et al., 2020. Quantifying deformation processes in the SE Pyrenees using U-Pb dating of fracture-filling calcites. Journal of the Geological Society, 177: 1186-1196.

Muñoz-López, D., et al. 2022. Spatio-temporal variation of fluid flow behavior along a fold: The Bóixols-Sant Corneli anticline (Southern Pyrenees) from U–Pb dating and structural, petrographic and geochemical constraints. Marine and Petroleum Geology, 143: 105788.