The Calabrian Arc and the Ionian Sea in the dynamic evolution of the Central Mediterranean

Abstract

In the Central Mediterranean area it is possible to recognize three main realms: the Tyrrhenian Sea, the Pelagian block and the Ionian block. These domains are limited by important fracture zones that are easily recognizable on land and offshore. These fracture zones can be grouped into four main trends: (1) the NW-SE trend which is characterized by dextral horizontal movements; (2) the NE-SW trend which is generally characterized by sinistral lateral horizontal movements; (3) the E-W trend which also shows dextral shear movements; and (4) the N-S trend which is characterized by normal faults only. The Tyrrhenian Sea realm is characterized by a thinned crust of oceanic type and is connected to the Apenninic chain by means of listric faults. From a geophysical point of view, the area shows a high heat flow which follows the main structural trends, and positive gravimetric anomalies which are compatible with seismic refraction data and can be explained by the proposed model. The Pelagian block shows a continental crust, about 20 km thick, which progressively increases beneath the Sicilian chain. Here an abrupt interruption with the Tyrrhenian block takes place. In the Pelagian realm, rifting processes developed according to the NW-SE and N-S trend. The N-S trend characterizes the westernmost zone of the realm where volcanic processes and a relatively high heat flow can also be observed. The Ionian block is characterized by the following: a thinned crust (17–20 km) which increases (40 km) towards the Southern Calabrian chain; a thick sedimentary sequence; high positive Bouguer anomalies (+300 mGal); and very low heat flow (50 mW m −2). Geophysical and structural analyses allowed us to evaluate the post-Tortonian evolution of the whole area under consideration. This evolution resulted in continental crust formation according to a rigid—plastic deformation model. According to our model, the Ionian block can be considered as a domain, characterized by a thinned continental crust and affected by intrusive material derived from the upper mantle. Furthermore, this domain, of probably Jurassic age, can be considered as a pelagic basin bordered by the Pelagian block to the west and by the Apulian block to the east-northeast. This basin, according to its position with respect to the Apenninic and Sicilian chains, has not been affected by tectogenesis and still represents a site of continuous sedimentation. From a kinematic point of view, the Ionian realm can be linked with the Pelagian block shifting towards the east-northeast, whereas it is limited towards the north by an E-W fracture zone which regulates the opening of the Tyrrhenian Sea and the counterclockwise rotation of the Apenninic chain. According to the proposed model, the opening of the Tyrrhenian Sea can be considered as a megaextension-fracture which developed parallel to the maximum principal stress direction and evolved as a triangular-shaped structural feature. In preparing the model the authors have taken into account a large set of data collected both on land and offshore.