GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 3.1 481 This evidence has induced some geophysics to hypothesize the existence of an Adriatic microplate, or alternatively of a promontory of the African megaplate (African Promontory; Channell et al. , 1979) located between the Neogene Apenninic and Dinaric-Hellenic thrust systems. It must be specified that the alternative concepts of microplate and African Promontory (Channell et al. , 1979) were born and were developed in the palaeogeographic and palaeotectonic setting of the Mediterranean area and then pertain to analytic methodologies and consequent interpretations, which not always are comparable among them. This is more true if the considered seismicity is concentrated in the first 50 km of lithosphere and then furnishes reliable information on the plate boundaries. Perhaps, when the authors refer to the present situation not always is clear how much it can be compared with that one of the pre-Neogene and pre-Cretaceous geologic past. It is worth to precise that the foreland areas should not to be considered as the stable and undeformed part located in front of a chain. In fact, due to the load induced from the lithospheric shortening of the chain, foredeep basins tend to form coupled with lithospheric bulges (Cloetingh, 1988). The stress field induced by the formation of a thrust belt may propagate from the collisional zones since to several hundreds of kilometers from the foreland. In conclusion it is worth recalling that for the area of Adria it has been observed based on gravimetric data a segmentation due to a sector evolution of the Apenninic chain, which has provoked a depocentral migration of the Plio-Quaternary foredeep (Royden et al. , 1987). This segmentation may explain the strike-slip structures, seismically active in the central-southern Adriatic Sea (Tremiti and Mattinata faults) apart from the plate margins. Mongelli and Ricchetti (1979) have considered the geodynamic roles of foreland and foredeep of the Apulian carbonate platform during the thrusting of southern Apennines. These authors have noted that the geodynamic role of the oceanic plates in the general schemes of global tectonics is developed by a continental microplate defined as the Apulian microplate. An analysis of the gravimetric and elastic characteristics of the Apulian microplate has been carried out in correspondence to the Bradanic foredeep and theApulian foreland. The microplate curved with an elastic behavior, downthrowing in the Bradanic foredeep and uplifting in correspondence to the Murge, due to the loading produced from the accumulation of Neogene- Quaternary sediments and for contemporaneous tangential shifts referred to the Apenninic thrusting. A geological-geophysical profile has been constructed (Fig. 2), crossing the Bradanic foredeep, the Murge foreland and the Adriatic sea, in order to show the geological structure of foredeep-foreland system related to southern Apennines. Fig. 2 – Geological - geophysical profile.