A regional structural model for the northern sector of the Calabrian Arc (southern Italy)

A SW-NE-oriented structural crustal section of northern Calabria (Southern Italy) extending from back-are (SW 'internal') up to foreland (NE. 'external') areas illustrates the tectonic evolution of this key sector of the Central Mediterranean Calabrian Are. The outcropping terrains of this part of Calabria show a thrust sheet pile of basement units ('Calabrian basement Complex'), which are from top to bottom: a Hercynian assemblage of gneisses, granites, and metapelites ('Calabride' Units), with a partly detached Jurassic-Paleogene cover and former foredeep sequences, a series of Alpine metamorphic units comprising a Cretaceous to Paleogene metapelitic/ophiolitic/carbonate assemblage ('Liguride' Units). This highly tectonized and cataclastic assemblage overlies a Triassic carbonate series that outcrops in a number of tectonic windows along the internal, Tyrrhenian side of the Are. Our field studies revealed that these can be assigned to the 'San Donato-Campotenese Unit' that shows a comprehensive Triassic pelitic to carbonatic platform series, more extensively outcropping in the northern part of the area. Along the external part of the section, well data show that the basement assemblage tectonically overlies a deformed carbonate unit and its Paleogene-Lower Miocene cover. These data confirm the hypothesis that the Calabrian basement was first deformed during Late Eocene (eo-Alpine phase) times and later overthrusted Tethyan carbonate platform areas, already deformed in the Apennine Chain. Highly detailed tectonostratigraphic studies of the Calabrian intra-arc and fore-are basins, previously published and recently calibrated with a regional interpretation of the available two-dimensional and three-dimensional seismic and well database, showed that the subsequent Late Neogene evolution was characterized by the activity of a number of oblique crustal shear zones that controlled the evolution of a wide range of thrust belt basins. Basin inversion phases during middle Messinian, middle Pliocene and middle Pleistocene times resulted in the widespread occurrence of thin-skinned and thick-skinned oblique back thrusting and the generation of regional passive roof duplex structures, all of these common along the margins and within the Calabrian Element. Our integrated interpretation of field geology, subsurface data and magnetotelluric analysis resulted in a comprehensive crustal section showing the following main features: (1) The superficial Calabrian basement Complex (assembled up to Eocene times) is a relatively thin thrust sheet (ca 1.5-2 km in thickness) overlying all deeper units. (2) Below this, an Early Miocene thrust stack in the subsurface shows a number of opposite (internal. W and external, E) verging tectonic units. The carbonate platform units outcropping in this northern sector of the Calabrian Are form the top part of this subsurface thrust stack. (3) Below the subsurface thrust stack, a number of antiformal geometries are present, which, in our opinion, are the fundamental crustal terranes of which the Calabrian Are is composed, juxtaposed by oblique crustal shear zones in Miocene-Recent times. The main branches of these shear zones, which root into a number of deep thick-skinned overthrusts, dissect and deform the Early Miocene thrust sheet pile and are represented by main transpressive fault zones in the surface. Three main subsurface terranes can be recognized: one internal, overlain by an internally verging thrust stack, one central overlain by a number of externally verging thrust sheets, and one externally in continuity with the foreland area. (4) Externally, a regional thin-skinned thrust sheet ('Metaponte Nappe') composed of a tectonic assemblage of Eocene and Late Neogene terrains shows a retrovergent internal margin that partly masks the surface trace of one of the major shear zones, and an external flat lying overthrust upon the Gulf of Taranto-Salentino foreland platform unit. Finally, we present an evolutionary model describing the Eocene to Recent evolution of this sector of the Central Mediterranean Mountain Chain. (C) 2000 Elsevier Science B.V. All rights reserved.