Gravity constraints on the dynamics of the crust-mantle system during Calabrian subduction

Abstract

The thermomechanic evolution of the lithosphere–upper mantle system during Calabrian sub- duction is analysed using a 2-D finite element approach, in which the lithosphere is composi- tionally stratified into crust and mantle. Gravity and topography predictions are cross-checked with observed gravity and topography patterns of the Calabrian region. Modelling results indi- cate that the gravity pattern in the arc-trench region is shaped by the sinking of light material, belonging to both the overriding and subduction plates. The sinking of light crustal material, up to depths of the order of 100–150 km is the ultimate responsible for the peculiar gravity signature of subduction, characterized by a minimum of gravity anomaly located at the trench, bounded by two highs located on the overriding and subducting plates, with a variation in magnitude of the order of 200 mGal along a wavelength of 200 km, in agreement with the isostatically compensated component of gravity anomaly observed along a transect crossing the Calabrian Arc, from the Tyrrhenian to the Ionian Seas. The striking agreement between the geodetic retrieved profiles and the modelled ones in the trench region confirms the crucial role of compositional stratification of the lithosphere in the subduction process and the cor- rectness of the kinematic hypotheses considered in our modelling, that the present-day config- uration of crust–mantle system below the Calabrian arc results from trench’s retreat at a rate of about 3 cm yr −1 , followed by gravitational sinking of the subducted slab in the last 5 Myr.