THE ANALYSIS OF SHEAR ZONES IN CALABRIA; IMPLICA TIONS FOR THE GEODYNAMICS OF THE CENTRAL MEDITERRANEAN

Systematic analysis of basement structures and Neogene morphotectonic elements -calibrated with research data on shear zones -has led to the construction of a new synthetic structural model for the Cala­brian Arc. Six fault systems can be distinguished which have generated various types of basins, such as piggy-back,pull-apart and complex oblique strike-slip basins. These systems are determined by three morphotectonic patterns: A) N130 trending segments separated by oblique transversal thrust zones. B) SW-NE trending thrust zones representing the most internal part of the Calabrian accretionary wedge system. C) Radial wedge-shaped segments confining the collapsed Southern Tyrrhenian Basin with accompanying concentric patterns of ten­sional faults internally and dome-shaped uplift centres situated externally, determining the actual arc. The pactterns A and B can be linked to the Serravallian-Early Pliocene development of crustal shear zones ("Strike-Slip Cycle") while pattern C can be linked to the Pleistocene development (extreme vertical tectonics). The Late Pliocene was characterised by a tensional regime. A scenario for the Neogene Central Mediterranean geodynamics has been developed by means of three mechanisms: 1) NE-SW compression (dextral shear along the N. African margin); 2) diapiric rise within the Tyrrhenian area and 3) roll-back and detachment of remnants of the subducted Ionian lithosphere ("passive subduction"). The interplay of these three mechanisms led to basal detachment and the gravitational displace­ment of che Calabrian Element to the SE, superimposed upon oblique overthrusting in the Apennines. A proto-Mediterranean shear zone pattern -evolved as a result of sinistral megatorsion of the northern hemisphere -controlled the development of the Central Medicerranean. -