Uplift vs. denudation in the southern Apennines (Italy): geomorphologic evidence and constraints from terrestrial cosmogenic nuclides and apatite (U-Th)/He data

Over a variety of mountain belts, evidence that erosion rates are comparable with exhumation rates supports the idea that, under steady uplift and over 103-106 yr time scales, mountain chains tend to achieve dynamic equilibrium between uplift and denudation. We investigate the relationships between uplift and denudation in the southern Apennines, a young orogen affected by crustal shortening until c. 0.7 Ma, and subsequently by regional uplift. The study is based on the integration of geomorphologic and morphometric data with constraints to the uplift and erosion rates. Quaternary marine terraces from the two sides of the mountain belt, and Pliocene-Pleistocene deposits from the chain axis, indicate that uplift coeval with shortening was both spatially and temporally uneven, and was slower than that (of c. 0.8 mm/yr) recorded after the ceasing of shortening. Constraints to the denudation are provided by (i) cosmogenic nuclides and long-term sedimentary yield, constraining erosion rates, and (ii) low-T thermochronometric data, constraining the unroofing of originally deeply buried tectonic units. Paleoerosion rates range from c. 0.2 to 0.4 mm/yr, and are consistent with the 0.6 to 0.3 mm/yr exhumation rates. Collectively, such values average denudation affecting most of the mountain belt, which includes bedrocks with variable resistance to erosion. Such results, which provide information on different time windows (collectively spanning from the Early Pleistocene to the Present), suggest that denudation averaged over long time spans is insensitive to climatic fluctuations. The overall data set indicates that the changing style and rate of uplift has not affected the development of denudation in the mountain belt. The imbalance between uplift and denudation, which is mirrored by the large-scale topographic features of the chain, appears as a result of the long response time of hillslope and fluvial systems with respect to the relatively young age of uplift acceleration.