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.