Burial and exhumation across the Alps–Apennines junction zone constrained by fission-track analysis on modern river sands

We applied fission-track analysis on modern river sands to constrain the Cenozoic evolution of the Alps–Apennines junction zone. West of the Villalvernia-Varzi-Ottone fault, samples yielded major peaks at 33–36 and 62–65 Ma, showing that apatites in the eroded wedge-top successions were largely unreset. To the east, samples yielded prominent peaks at 4.0–4.7, 6.5–6.7 and 19 Ma, probably formed by reset ages. Our results indicate that the Alpine orogenic wedge originally tapered out to the south. The Northern Apennines were buried beneath a thick and widespread Epiligurian cover, now almost completely eroded, and experienced major uplift and erosional exhumation since early Pliocene times, at average rates of 1 km Ma−1. A large amount of Alpine-derived detritus, previously stored on top of the orogenic wedge, was transferred into the Po Plain. Sediment recycling thus overwhelmed any eventual effect of climate change on Plio-Quaternary sedimentation rates south of the Alps.