Abstract

Integration of surface and subsurface geological, structural and geophysical data has allowed us to interpret the thrusts of the frontal and external sector of the Apennine chain as the expression of a lithospheric Apennine Neo-Chain oriented NW-SE, forming since the Pliocene. In this context, in the Apennine orogenic system three separate overlapping chains can be recognized, involving distinct structural levels: a) remnants of the most superficial portion of the Alpine chain constituted by sedimentary covers with local portions of oceanic basement (Liguridi s.l.); b) the crustal Oligocene-Miocene Apennine Paleo-Chain; c) the lithospheric Pliocene-Quaternary Neo-Chain. The lithospheric character of the Apennine Neo-Chain is peculiar for such an orogeny with respect to the other orogenic systems that are characterized by a thin-skinned tectonic style in the external portion. The development of the Neo-Chain induced a strong uplift and erosion of the Paleo-Chain with a total change of the foredeep infilling process, which assumed the character of a molasse. Two principal evolution stages can be recognized during the Neo-Chain development: A) Lower Pliocene-Middle Pliocene; B) Upper Pliocene-Lower Pleistocene. The first stage is characterized by important thrust components. Instead in the second stage,.in the Southern Apennines, transpressive deformation and the development of N-S and E-W trending faults prevail, with right- and left-lateral strike-slip kinematics, respectively. We believe it likely that the asthenospheric upwelling in the Tyrrhenian area, related to the Southern Apennines-Arco Calabro Miocene subduction, could have favored, since the Lower Pliocene, a mainly NE-ward lateral extrusion, induced by the Africa-Europe convergence. The development of the lithospheric Neo-Chain with strong translation for thrusting until the Upper Pliocene may be related to this process. In fact, the lithospheric thickness variations of the undeformed Adria block could have produced the development of this Neo-Chain, oblique with respect to the direction of the Africa-Europe convergence, as supported by the analogical models (Sokoums et alii, 2000). Since the Middle Pleistocene, the evolution of the Apennine Chain and related foreland has been directly controlled by the Africa/Adria NNW motion with respect to the Europe block. This convergence, associated with the Adria CCW rotation (Meletti et alii, 2000), produced the Late Quaternary activity of the lithospheric thrust in the Central-Northern Apennine Neo-Chain with transpressive kinematics, as documented by the seismicity (Selvaggi, 2001). This transpressive kinematics characterized the westernmost sector of the Northern Apennines up to the Turin Hill, as proposed by Schumacher & Laubscher (1996). Toward the east, in the foreland area, NNW-SSE trending faults, such as the Schio-Vicenza/Middle Adriatic Ridge system, allowed NNW differential motion of the Adria blocks in the footwall of the active thrust fronts of the Southern-Alps. E-W trending right-lateral faults, such as the Mattinata fault, fragmented the Adria block in its southern sector. These faults are characterized by a seismo-tectonic significance as documented by the seismicity. In the Southern Apennines, the Adria plate CCW rotation produces the negative inversion of the Neo-Chain thrusts. In the axial zone of the Apennines, the normal faults and associated seismicity can be related to the uplift induced by the asthenospheric upwelling.

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