Timing and distribution of exhumation in the Ebro basin reveal a plate-scale 10 Ma geodynamic event
Résumé
The interplays between deep geodynamic processes and Earth-surface erosion processes control the elevation and distribution of land masses, which in turn control environmental changes. These interactions can be best evaluated in post-orogenic landscapes defined by decaying crustal deformation. This is the case of the Iberia peninsula where a growing body of geological evidence suggests the existence of a post-orogenic erosion around 10 Ma, well documented across the Pyrenees. Different mechanisms have been proposed, including lithospheric and sublithospheric processes, and Earth-surface processes triggered by base-level change and/or climate forcing on erosion. Here, we focus on the Ebro basin, which was a closed basin that opened towards the Mediterranean in the late Miocene. The distribution and exact timing of erosion in the Ebro basin are, however, only partially known, and do not yet allow resolving the post-orogenic mechanisms involved. We present new (U-Th-Sm)/He dates on apatite obtained in sandstones distributed from the edges of the Ebro basin to its center. The results of the thermal modelling confirm that the exhumation of the Ebro Basin took place between 12 and 6 Ma, or around 10 Ma when accounting for model uncertainties. Reconstruction of the sediment infill reveals that the late Miocene post-orogenic deposits were the thickest, between 1 and 1.6 km, near the topographic front of adjacent mountain ranges and were the thinnest, approximately 300 m, in the center. The exhumation in the Ebro basin occurred after shortening has stopped, and before the Messinian Salinity Crisis. It is consistent with the widespread 10 Ma-exhumation event documented throughout Iberia, from the Aquitaine basin to the Betic Cordillera, and provides evidence of large-scale lithospheric and sublithospheric processes that coincide with the cessation of slab retreat in the West Mediterranean. We propose that a plate-scale uplift driven by deep-seated processes is the main cause of the Ebro basin incision. The response of the landscape to this geodynamically controlled erosion event led to a complex tectonic reorganization, e.g. along the strike of the Pyrenees, environmental changes in the Mediterranean, leading to the Messinian Salinity Crisis, and faunal turnover over Iberia.