Evoluzione tettonica quaternaria della Pianura Padana centro-orientale e dei suoi margini

Abstract

: The Southalpine and Apenninlc foothills along the Po Plain have been deformed by still active extensions tectonic movements, which are superimposed on previous compression features. Timing and causes of the tectonic activity in the two foothill belts are different Extensional processes along the Southalpine foothills started in Early Pliocene times as the consequence of the peripheral bulging of the Apennine foredeep. The North-Apenninic foreland system, in fact, has been in its present geographic position since the Late Messinian, bringing about the progressive weakening and uplifting of its peripheral bulge. Extension along the North-Apenninic foothills started in the middle Pleistocene in the Bologna area, with the activity of a SW-dipping master fault with a >1000 m throw, which seems to be kinematically connected with the Tyrrhenian extension. The hangingwall is deformed by anti-tethic NE-dipping normal faults, along which fluid vents have been identified. The footwall is greatly tilted toward the Po Plain: the tilting rate in the middle Pleistocene to Holocene foothill deposits was evaluated to be 0.15°/10,000 years. A secondary stress field with horizontal a-i characterized the downward flexed hinge of the footwall, and was not associated with contractions tectonic activity. The described features affect the foothill margin, whereas the stress field in the subsiding Po Plain is possibly still compressional, as suggested by earthquake fault plane solutions. On the basis of the present collisional setting, we assume that extension in the upper crust and compression at lower lithospheric levels could be contemporaneous processes.