PALEOMAGNETIC AND STRUCTURAL EVIDENCE FOR NEOGENE BLOCK ROTATIONS IN THE CENTRAL APENNINES ITALY

Magnetic fabric and paleomagnetic analyses on sedimentary sequences in several structural units in the Central Apennines ranging from upper Cretaceous pelagic carbonates to upper Miocene turbidites provide evid ence for at least two distinct phases of rotation. The first countercl ockwise (CCW) rotation is well recorded in Eocene-Oligocene sediments and does not affect the lower-middle Miocene sequences. The second pha se is clearly recorded in lower-middle and upper Miocene sediments and shows both CCW and clockwise (CW) rotations in concordance with trend s of the different thrust structures. We detected three domains charac terized by different rotation patterns. The westernmost is the souther n Sabina area, an arcuate thrust belt which underwent a CW rotation af ter the early Miocene. The second domain is the Latium-Abruzzi carbona te platform, where a CCW rotation occurred after the late Miocene. The third is the Marsica area that underwent a CW rotation after the late Miocene. The magnetic fabric analyses confirm the existence of these different structural provinces and show a strong correlation between t he present-day strike of the anisotropy of magnetic susceptibility mag netic lineation and the rotations recorded in Miocene sediments. We at tribute present-day variations in orientation of the compressional str uctures in the Central Apennines to differential rotations about verti cal axes due to strike-slip faults and out of sequence thrust activity , rather than to a change in the stress field orientation. We also sug gest that this deformation mechanism could be common in other collisio nal chains around the world.