Low-angle normal faulting and focused exhumation associated with late Pliocene change in tectonic style in the southern Apennines (Italy)
Mazzoli S.1, Ascione A.1, Buscher J.T.1, Pignalosa A.2, Valente E.1, Zattin M.3
Tectonics, 33(9), 1802-1818, 2014
In the southern Apennines, low-temperature thermochronometry data indicate that exhumation of previous tectonically buried sedimentary units started at around 10Ma and took placemostly during the last 6Ma. Relatively high exhumation rates are obtained from apatite fission track (AFT) and (U-Th)/He (AHe) analysis, pointing to a substantial contribution of tectonic processes to rock exhumation besides erosion. Exhumation rates derived fromnew apatite (U-Th)/He data (AHe) for the last 3Ma are generally lower than rates determined by AFT data and almost in line with erosion rates inferred from cosmogenic nuclides and sediment yield, thus suggesting that tectonic exhumation was dominant during the older exhumation stages of this region. However, younger cooling ages in the Monte Alpi area from both AFT and AHe analyses point out focused exhumation during the last 3Ma. Structural and morphotectonic analyses indicate that fast exhumation occurred specifically in this area—where the Apulian Platform reservoir carbonates, elsewhere buried beneath a several kilometer-thick allochthonous cover, are exposed at the surface—as a result of a complex interplay between steep-rooted reverse faulting and shallow low-angle extension. This deformation involved the development of foreland-dipping low-angle normal faults affecting the allochthonous cover units during the late stages of reverse fault-related anticlinal growth in the underlying buried carbonates. Extension of the region triggered focused exhumation in the footwall of the extensional low-angle faults, which was followed by widespread crustal extension and associated development of high-angle normal faults, leading to surface uplift of Monte Alpi.
(a) Geological sketch map of the study area (modified from Ascione et al. ) with inset showing Italian peninsula, with northern, central, and southern Apennines, and Apulian foreland. Labels of samples analyzed in this work are shown in blue. AFT ages (representing age of cooling through the closure temperature defined for each sample; see text) are shown in black in mega annum (±standard deviation). AFT cooling ages [Corrado et al., 2005; Iannace et al., 2007; Mazzoli et al., 2006, 2008; Invernizzi et al., 2008] are integrated with new apatite (U-Th)/He cooling ages shown in red beside AFT ages obtained for the same sample. The box indicates location of the geological map in Figure 2. Shaded relief map created from 90m SRTM data. (b) Regional cross section (modified from Mazzoli et al. ).