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. 'externa l') areas illustrates the tectonic evolution of this key sector of the Cent ral 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 bot tom: a Hercynian assemblage of gneisses, granites, and metapelites ('Calabr ide' Units), with a partly detached Jurassic-Paleogene cover and former for edeep sequences, a series of Alpine metamorphic units comprising a Cretaceo us to Paleogene metapelitic/ophiolitic/carbonate assemblage ('Liguride' Uni ts). This highly tectonized and cataclastic assemblage overlies a Triassic carbonate series that outcrops in a number of tectonic windows along the in ternal, Tyrrhenian side of the Are. Our field studies revealed that these c an be assigned to the 'San Donato-Campotenese Unit' that shows a comprehens ive Triassic pelitic to carbonatic platform series, more extensively outcro pping in the northern part of the area. Along the external part of the sect ion, well data show that the basement assemblage tectonically overlies a de formed carbonate unit and its Paleogene-Lower Miocene cover. These data con firm the hypothesis that the Calabrian basement was first deformed during L ate 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 regio nal interpretation of the available two-dimensional and three-dimensional s eismic and well database, showed that the subsequent Late Neogene evolution was characterized by the activity of a number of oblique crustal shear zon es that controlled the evolution of a wide range of thrust belt basins. Bas in inversion phases during middle Messinian, middle Pliocene and middle Ple istocene times resulted in the widespread occurrence of thin-skinned and th ick-skinned oblique back thrusting and the generation of regional passive r oof duplex structures, all of these common along tile margins and within th e Calabrian Element. Our integrated interpretation of field geology, subsurface data and magneto telluric analysis resulted in a comprehensive crustal section showing the f ollowing main features: (1) The superficial Calabrian basement Complex (ass embled up to Eocene times) is a relatively thin thrust sheet (ca 1.5-2 km i n thickness) overlying all deeper units. (2) Below this, an Early Miocene t hrust stack in the subsurface shows a number of opposite (internal. W and e xternal, E) verging tectonic units. The carbonate platform units outcroppin g in this northern sector of the Calabrian Are form the top part of this su bsurface thrust stack. (3) Below the subsurface thrust stack, a number of a ntiformal geometries are present, which, in our opinion, are the fundamenta l crustal terranes of which the Calabrian Are is composed, juxtaposed by ob lique crustal shear zones in Miocene-Recent times. The main branches of the se 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 te rranes can be recognized: one internal, overlain by an internally verging t hrust stack, one central overlain by a number of externally verging thrust sheets, and one externally in continuity with the foreland area. (4) Extern ally, a regional thin-skinned thrust sheet ('Metaponte Nappe') composed of a tectonic assemblage of Eocene and Late Neogene terrains shows a retroverg ent 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 Tarant o-Salentino foreland platform unit. Finally, we present an evolutionary model describing the Eocene to Recent e volution of this sector of the Central Mediterranean Mountain Chain. (C) 20 00 Elsevier Science B.V. All rights reserved.