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Alessandra Ascione, Università di Napoli (Italy)
Aldo Cinque, Università di Napoli (Italy)
Stefano Mazzoli, Università di Napoli (Italy)
Antonio Pignalosa, Università di Bologna (Italy)
Ettore Valente, Università di Napoli (Italy)
Massimiliano Zattin, Università di Bologna (Italy)
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The southern Apennines fold-and-thrust belt resulted from Tertiary to Quaternary shortening, with eastward motion of allochtonous units over the Apulian foreland, and coeval extension with formation, to the west of the chain, of the Tyrrhenian basin.
The topography of the southern Apennines displays some peculiar features, e.g. a low elevation to relief ratio and a main divide following neither the highest crests nor the chain axis. Furthermore, this chain features an asymmetric shape, with the eastern slope displaying a lower dip than the western one and maximum elevations mostly located to the west of the chain axis, in spite of the larger and faster Quaternary uplift experienced by the eastern slope. Furthermore, the geomorphological-stratigraphical constraints from the chain interiors point to a markedly uneven time-space distribution of Pliocene-Quaternary absolute vertical motions across the chain.
In order to unravel the relief formation history of this young orogen, we integrated geomorphological, stratigraphical, structural and apatite fission track and U-Th/He data useful to constrain timing and amount of absolute and differential vertical motions. The integrated approach points out that the evolution of the relief resulted from the complex interaction of several processes. In particular, the marked asymmetry of the orogen mainly results from the interaction between different extensional processes that have been active since the latest Tertiary. The smoother topography of the eastern slope may in fact be considered as the response to Pliocene-early Quaternary large-scale gravitational collapses that affected different portions of the chain during different time spans. This caused exhumation of formerly buried units that underwent relatively fast rock uplift and coeval surface uplift. These relatively shallow processes coexisted with deep-seated extension active at the western side of the chain. The eastward migration of this latter crustal extension caused major downthrowing of large portions of the chain along high angle normal faults. This process is mirrored by the steeply sloping western flank of the chain, which is also punctuated by several coastal grabens. The interaction of the two different extensional processes largely controlled the amount and distribution of surface uplift until the beginning of the Middle Pleistocene, and caused major reorganization of the drainage net. Following the cessation of shortening, large-scale surface uplift affected the chain since the Middle Pleistocene. The amount of this final uplift tends to increase regularly from the east towards the chain axis, and to decay sharply towards the western flank of the chain affected by crustal extension. Uplift was accompanied by extension that, at the chain axis, led to the formation of several intramontane basins and triggered further drainage net reorganization.
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