Structural architecture of the Central Apennine: Interpretation of the Crop 11 seismic profile from the Adriatic coast to the orographic divide

We present an interpretation of the eastern halfportion of the CROP 11 line, a deep reflection seismicprofile 265 km long that cuts across the centralApennines from the Tyrrhenian coast to the Adriaticcoast. In the study area the line cuts across a pile ofthrust sheets that underwent tectonic transport betweenthe Messinian and the Pleistocene. In its easternmostpart, the line runs through the Plio-Pleistocene depositsof the Adriatic foredeep. In the foreland region theCROP 11 line integrates previous information on thecrustal structure derived from petroleum explorationand from deep seismic sounding refraction experiments.In particular, the CROP 11 line confirms the existenceof a very thick sedimentary sequence underlying theMesozoic-Tertiary carbonates of the Apulia Platforminterpreted as the Paleozoic-Triassic sedimentary coverof a pre-Cambrian crystalline basement. In the mountainchain, where the base thrust of the orogenic wedge reachesa depth of about 25 km, this sedimentary sequence appearsto be the deepest geological unit incorporated in the thrustsystem. This interpretation of the CROP 11 profilesuggests an unusual thin-skin tectonic style implyingthe detachment from the original basement and theincorporation in the post-Tortonian tectonic wedge of avery thick Paleozoic-Triassic sedimentary sequencepossibly affected by low-grade metamorphism in thelower part. Other new suggestions from the CROP 11seismic data concern the origin of the Fucino basin, oneof the most remarkable Plio-Pleistocene intramontanebasins. The normal faults bordering this structuraldepression, as other important normal faults present inthe central Apennines (e.g., the Caramanico fault systemin the Majella region), seem to have been controlled bygravitational-collapse processes driven by uplift duringcrustal shortening rather than by a generalized extensionsubsequent to the Apennine compression, as usuallyreported in the geological literature. If this interpretationis correct, the strong seismic activity in correspondenceto the Apennine watershed may be related to the veryrecent increase in the structural relief caused by an outof-sequence propagation of the active thrusts.