Structural architecture of the central Apennines: Interpretation of the CROP 11 seismic profile from the Adriatic coast to the orographic divide

We present an interpretation of the eastern half portion of the CROP 11 line, a deep reflection seismic profile 265 km long that cuts across the central Apennines from the Tyrrhenian coast to the Adriatic coast. In the study area the line cuts across a pile of thrust sheets that underwent tectonic transport between the Messinian and the Pleistocene. In its easternmost part, the line runs through the Plio-Pleistocene deposits of the Adriatic foredeep. In the foreland region the CROP 11 line integrates previous information on the crustal structure derived from petroleum exploration and from deep seismic sounding refraction experiments. In particular, the CROP 11 line confirms the existence of a very thick sedimentary sequence underlying the Mesozoic-Tertiary carbonates of the Apulia Platform interpreted as the Paleozoic-Triassic sedimentary cover of a pre-Cambrian crystalline basement. In the mountain chain, where the base thrust of the orogenicwedge reaches a depth of about 25 km, this sedimentary sequence appears to be the deepest geological unit incorporated in the thrust system. This interpretation of the CROP 11 profile suggests an unusual thin-skin tectonic style implying the detachment from the original basement and the incorporation in the post-Tortonian tectonic wedge of a very thick Paleozoic-Triassic sedimentary sequence possibly affected by low-grade metamorphism in the lower part. Other new suggestions from the CROP 11 seismic data concern the origin of the Fucino basin, one of the most remarkable Plio-Pleistocene intramontane basins. The normal faults bordering this structural depression, as other important normal faults present in the central Apennines (e.g., the Caramanico fault system in the Majella region), seem to have been controlled by gravitational-collapse processes driven by uplift during crustal shortening rather than by a generalized extension subsequent to the Apennine compression, as usually reported in the geological literature. If this interpretation is correct, the strong seismic activity in correspondence to the Apennine watershed may be related to the very recent increase in the structural relief caused by an outof-sequence propagation of the active thrusts.