The Permo-Carboniferous Basins of the Catalan Pyrenees (NE Iberia): An Example of Interacting Tectonics and Collapse Calderas

Abstract

The Permo-Carboniferous terrains of the Catalan Pyrenees show evidence of extensive calc-alkaline orogenic volcanism with predominant pyroclastic deposits of dacitic to rhyodacitic composition. These Permo-Carboniferous basins have been interpreted as volcano-tectonic depressions associated with a transtensional regime following the Variscan orogeny. The incorporation of the Permo-Carboniferous basins into allochthonous Alpine units produced their verticalization and unrooting, and consequently, their original position, size, and structure are not yet well constrained, nor is the total volume of volcanic material. Thus, to get better insights into the characteristics of the Permo-Carboniferous volcano-tectonic basins, we conducted a structural analysis of a particular sector of the Catalan Pyrenees, the Nogueres Zone, by combining detailed field work with cross-section balancing and restoration techniques. As such, we provide a comprehensive 3D palinspastic restoration of the Permo-Carboniferous basins to identify their relative original positions, dimensions, and internal structures. The results of this structural restoration highlight the occurrence of syndepositional faults and enhance calculation of the volcano-clastic volume preserved within the basin. The linkage between these faults and the architecture of the basins' fill indicating large caldera collapse episodes during the Permo-Carboniferous, suggest a tight interaction between a transtensive fault system and a shallow magmatic system. In this scenario, we propose that the catastrophic events responsible for the deposition of the main volumes of volcanic materials were controlled by the same fault systems that drove the tectonic subsidence of these basins. These results highlight the importance of the regional tectonic setting in the formation of large caldera systems.