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

Abstract

AbstractIn 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 (~1 mm/yr) was distributed roughly equally between both margins over some 20 Myr. A quiescent phase (Paleocene) was apparently restricted to the retro‐wedge with slow, continuous deformation in the pro‐wedge (~0.4 mm/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 (~3.1 mm/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 (~2.2 mm/yr). Minimum total shortening of the Eastern Pyrenees is ~111 km, excluding closure of the exhumed mantle domain. The retro‐wedge accommodated ~20 km 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.