Quaternary uplift of southern Italy


  • Rob Westaway


Dramatic coastline changes demonstrate rapid Quaternary uplift of Calabria in southern Italy. Because most of the west (Tyrrhenian Sea) coast is normal fault bounded, previous work has asserted that its uplift is local footwall uplift related to extension. However, the east (Ionian Sea) coast is also uplifting but is not normal fault bounded. This reanalysis, based on original fieldwork and reinterpretation of the literature, reaches the following conclusions. First, although radiometric dating of only one marine terrace sequence in Calabria is available, on the east coast at Crotone, terraces occur at similar elevations, and can thus be correlated, throughout this coast and the west coast of northern and central Calabria. Uplift rate at both coasts and across the region in between is the same, 1.0 ± 0.1 mm yr−1, provided my correlations are correct. Second, the oldest raised shorelines date from the 0.9 Ma marine highstand and have uplifted ∼700 m since ∼0.7 Ma. Regional uplift rate earlier was minimal, possibly zero. Third, localities on this west coast show marginally (up to ∼5%) higher uplift rates, indicating some local footwall uplift (at ∼0.05 mm yr) associated with slow extension (at ∼0.1 mm yr−1). Fourth, the 12-m Holocene marine terrace formed around 7 ka. Allowing for a 3-m range of wave and tidal action, it is interpreted as the result of 7 m of tectonic uplift and 2 m of eustatic sea level fall during ∼6–4 ka. Finally, the west coast of southern Calabria shows significant elevation changes caused by active normal faulting, as well as regional uplift. Footwall localities have uplifted up to 1300 m since 0.9 Ma. The estimated maximum present-day uplift rate of 1.67 mm yr−1 is interpreted as 1 mm yr of regional uplift plus 0.67 mm yr of local footwall uplift, indicating much faster extension than farther north. It is suggested that the Tyrrhenian Benioff zone detached from beneath Calabria shortly before 0.7 Ma. The regional uplift of the overlying landmass is thus explained as its transient isostatic response to removal of this load. Order-of-magnitude calculations suggest that 1 mm yr−1 uplift rate is reasonable, with ∼2 km total uplift expected, indicating that uplift will continue for > ∼1 Myr into the future. Extension of Calabria appears to have begun at ∼11 Ma, at the same time as formation of the Tyrrhenian Sea and the related subduction at its Benioff zone. Extension rate in southern Calabria abruptly increased from ∼0.1 to ∼1 mm yr−1 around 0.9–0.7 Ma., when the slab detached and the regional uplift began; extension in northern and central Calabria continues at the same ∼0.1 mm yr−1 rate as before.