Detrital apatite fission-track ages from the Po sands: Implications for the erosional pattern of the orogenic source areas

Fission-track dating on detrital apatites from modern sands of the Po delta is employed for a provenance study of sediments in the Po River drainage. Analysed samples show a fission-track grain-age distribution characterized by a well-resolved peak at 10 Ma, beside two other peaks at 19 and 40 Ma. The youngest peak is significantly larger than the older peaks, and accounts for 63% of the total population of dated grains. This young component in the grain-age distribution is consistent with the bedrock cooling ages observed in the Western Alps between the External Massifs and the Houiller unit, as well as in the Lepontine dome of the Central Alps and in the Miocene foredeep units of the Apennines. These potential source areas represent only 10% of the total orogenic source area of the Po drainage. The above results suggest that most of the sediment delivered to the Po delta is supplied by small portions of the drainage that represent in many cases (Lepontine dome and External Massifs) fast-exhuming portions of the belt bounded by major faults.