Paleomagnetic evidence for a post‐Eocene 90° CCW rotation of internal Apennine units: A linkage with Corsica‐Sardinia rotation?

Abstract

We report on an extensive paleomagnetic study (36 sites) of the Tuscan Nappe succession from the Northern Apennines Arc, aimed to reconstruct the tectonic evolution of the internal sector of this chain. We analyzed Eocene pelagic foreland ramp deposits (Scaglia Toscana Formation) and Oligocene-lower Miocene siliciclastic turbidites (Macigno and Falterona Formations). Paleomagnetic results show that the internal sector of the Northern Apennines underwent large counterclockwise (CCW) rotations with respect to the Adria-Africa foreland. A decrease in the rotation magnitude was observed from the southern to the northern sector of the arc (from 91 to 36°). This trend is opposite to that observed in the more external units of Northern Apennines and demonstrates that the oroclinal bending model, which has been proposed for the external units of the chain, is not appropriate to explain the evolution of the internal sector of the arc. On the basis of the observed paleomagnetic pattern, we propose a new tectonic model in which the Tuscan and Falterona-Cervarola units in the southern area were first rotated CCW along with the Corsica-Sardinia block during its lower Miocene rotational drifting and were later involved in the main phases of rotational emplacement and translation toward the outermost sector (Umbria domain), thus yielding the final curved shape of the Northern Apennines chain. Data from this study represent the first paleomagnetic evidence of the influence of the Corsica-Sardinia CCW rotation in the Apennines orogenic wedge deformation, in the general framework of the geodynamic evolution of the Central Mediterranean subduction system.

From cylindrical to non‐cylindrical foreland basin: Pliocene–Pleistocene evolution of the Po Plain–Northern Adriatic basin (Italy)

“…Geodynamic and paleogeographic reconstructions describe the NNE‐wards migration of the northernmost sector of Apennines belt progressively turning perpendicular to the Mesozoic inherited lineaments (Figure c). The change in vergence was due to the anticlockwise rotation of the collisional system during the drifting of the Corsica–Sardinia block, with rotation pole located in the Ligurian Sea (Caricchi et al, ; Gattacceca et al, ). The emplacement of the Emilia and Ferrara arcs (during Messinian and Pleistocene, respectively) in the middle part of the PPAF, completely separated the foredeep into distinct depocentres (Figure c, d).…”

The role of carbon from recycled sediments in the origin of ultrapotassic igneous rocks in the Central Mediterranean

“…The subducted slab rolled back, eastward, and the Apennine orogeny also moved eastward (anticlockwise) (Civetta et al, 1978;Channell, 1996;Faccenna et al, 2001Faccenna et al, , 2004Savelli, 2002;Caricchi et al, 2014). At the beginning of the Eocene the area between Corsica and Tuscany underwent post-orogenic extension, with initial opening of the Tyrrhenian basin and uprising of the asthenospheric mantle (e.g., Doglioni, 1991;Jolivet et al, 1996;Malinverno and Ryan, 1986) and subsequently of associated geotherms.…”

Distinct magnetic fabric in weakly deformed sediments from extensional basins and fold-and-thrust structures in the Northern Apennine orogenic belt (Italy)

“…Subsequently, during Oligocene‐lower Miocene time the Tuscan units were incorporated in the orogenic wedge, which progressively involved the more external sector of the chain. During this process, the magnetic lineation passively rotated counterclockwise to follow the formation of the Northern Apennine arc [ Caricchi et al ., ]. The parallelism with the main tectonic structures of the chain was therefore maintained.…”

“…The hysteresis loops obtained after correction for the paramagnetic slope are consequently poorly defined and indicate the presence of very low amounts of low‐coercivity ferrimagnetic minerals. The obtained B cr values (in the range 30–45 mT) (Figures b and c) and the available rock magnetic data [see also Caricchi et al ., ] indicate that the very weak remanent signal in these deposits is carried by magnetite. The hysteresis data of the postorogenic deposits indicate a distinct ferromagnetic (in a broad sense) contribution with the presence of low‐coercivity minerals in the pseudosingle to multidomain range grain sizes (Figures d and e).…”