The transition from convergence to extension in the NW Mediterranean: insights from the thermochronologic and tectono-sedimentary record in the Eastern Pyrenees and Empordà basin (NE Spain)

The Empordà basin is located in NE Catalonia (Spain), overprinting the Eastern Pyrenees where this mountain belt reaches the Mediterranean Sea. The area offers an opportunity to study cycles of orogenic evolution, from mountain building to destruction, although with some peculiar features. Following Pyrenean contractional structures that ceased in the Oligocene, earlier than in the Central and Western Pyrenees finished during the lower Miocene, the extension that depressed the Empordà basin seems to be a younger event (late Miocene-Pliocene) than the opening of the Western Mediterranean (Gulf of Lyon and Valencia trough; late Oligocene-Miocene). The regional NE-SW extensional fault systems that dominate from the Gulf of Lion to the Catalan Coastal Ranges and Valencia grabens contrast with the NW-SE normal faults in the Empordà basin, which are also associated with alkali volcanism during the Neogene. This feature is still poorly understood, together with the absence of crustal root in the adjacent relict relief of the Pyrenees despite the relatively high elevation.

To gain insights into these questions and into the detailed geochronology and mechanisms of the transition from convergence to extension, we have revisited the tectono-sedimentary record of the South-Pyrenean and Empordà basins. First, the provenance of the clastic deposits from the Paleogene to the Neogene gives information about the evolution of the sedimentary systems, as well as the tectonic changes in the source regions. This data combined with low-temperature thermochronology of source reliefs and basin sedimentary units allows characterizing part of the geodynamic evolution from the NW Mediterranean realm. Complementary, new structural data from field observations and seismic profile interpretation provide us with inferences on a new structural model of the region.