Insights Into the Crustal‐Scale Dynamics of a Doubly Vergent Orogen From a Quantitative Analysis of Its Forelands: A Case Study of the Eastern Pyrenees

In natural doubly vergent orogens, the relationship between the pro- and retro-wedges is, as yet, poorly constrained. We present a detailed tectonostratigraphic study of the retro-wedge of the Eastern Pyrenees (Europe) and link its evolution to that of the pro-wedge (Iberia) in order to derive insight into the crustal-scale dynamics of doubly vergent orogens. Based on cross-section restoration and subsidence analyses, we divide the East Pyrenean evolution into four phases. The first phase (Late Cretaceous) is characterized by closure of an exhumed mantle domain between the Iberian and European plates and inversion of a salt-rich, thermally unequilibrated rift system. Overall shortening (similar to 1mm/yr) was distributed roughly equally between both margins over some 20Myr. A quiescent phase (Paleocene) was apparently restricted to the retro-wedge with slow, continuous deformation in the pro-wedge (similar to 0.4mm/yr). This phase occurred between closure of the exhumed mantle domain and onset of main collision. The main collision phase (Eocene) records the highest shortening rate (similar to 3.1mm/yr), which was predominantly accommodated in the pro-wedge. During the final phase (Oligocene), the retro-wedge was apparently inactive, and shortening of the pro-wedge slowed (similar to 2.2mm/yr). Minimum total shortening of the Eastern Pyrenees is similar to 111km, excluding closure of the exhumed mantle domain. The retro-wedge accommodated similar to 20km of shortening. The shortening distribution between the pro- and retro-wedges evolved from roughly equal during rift inversion to pro-dominant during main collision. This change in shortening distribution may be intrinsic to all inverted rift systems.