Paleomagnetic constraints on the Plio¯Pleistocene geodynamic evolution of the external central¯northern Apennines (Italy)

Pantelleria is a volcanic island situated at the centre of the Sicily Channel continental rift. Since 1980, the island has been monitored by geodetic techniques (electro-optical distance measurements (EDM) and levelling) and gravimetry. After more than 10 years, the EDM network was re-measured in 1995 and successively it has been improved and measured also with global position system (GPS) techniques. It has therefore been possible to carry out a long-term analysis (1980¯1996) of the deformation pattern. The levelling in the 1980¯1996 period revealed a marked lowering of the central-southern part of the island with respect to the northern sector. The horizontal EDM measurements all prove to be in contraction and suggest that a deflation is ongoing in the central-southern part. The effects of areal contraction and lowering are interpreted as being due to the volcanic field, which appears to predominate over possible stretching induced by the Sicily Channel dynamics. We modelled the horizontal and vertical changes accumulated over 16 years using a 3D ellipsoidal depressuring model which indicates a ca. 5 km deep source located under the area within the most recent caldera. This model could explain a short term (tens of years) acting deflation. We also propose an interpretive framework in the case where the deflation is acting over a long period (thousands of years). In this case, the deflation is interpreted as readjustment following the loss of mass occurring with recent volcanism (18¯3 kyr).