From nappe stacking to out‐of‐sequence postcollisional deformations: Cretaceous to Quaternary exhumation history of the SE Carpathians assessed by low‐temperature thermochronology

Apatite fission track (AFT) and (U‐Th)/He (AHe) thermochronology have been combined to constrain the exhumation history of the SE Carpathians. Cooling ages generally decrease from Cretaceous for the internal basement nappes (AFT ages), to Miocene–Quaternary (AFT and AHe, respectively) for the external sedimentary wedge. The AFT and AHe data show a Paleogene age cluster, which confirms a suspected but never demonstrated tectonic event. The new data furthermore suggest that the SE Carpathians have been affected by a middle Miocene exhumation phase related to continental collision, which occurred at rates of ∼0.8 mm/yr, similar to the one previously inferred for the East Carpathians. The SE Carpathian tectonic evolution, however, is overprinted by two younger exhumation events in the Pliocene–Pleistocene. The first exhumation phase (latest Miocene–early Pliocene) occurred at high exhumation rates (∼1.7 mm/yr) and is interpreted as a tectonic event and/or associated with a sea level drop in the Paratethys basins during the Messinian low stand. The youngest recorded tectonic phase suggests rapid Pleistocene exhumation (∼1.6 mm/yr) and is interpreted to represent crustal‐scale shortening different in mechanics from collisional processes. The data suggest that the SE Carpathians did not develop as a typical double‐vergent orogenic wedge; instead, exhumation was related to a foreland‐vergent sequence of nappe stacking during collision and was subsequently followed by a large out‐of‐sequence shortening event truncating the already locked collisional boundary.