Paleomagnetism of the Gran Sasso Range Salient (Central Apennines, Italy): pattern of orogenetic rotations due to translations of a massive carbonate indenter.

We report on the paleomagnetism (39 new sites) of Gran Sasso, an indenter-controlled salient of the external central Apennines formed by two orthogonal limbs. We find that Gran Sasso is a complex salient, paleomagnetically corresponding to neither a nonrotating nor an oroclinal end-member. Data from the core of the arc show that the indenter itself did not undergo any rotation. Conversely, rotations of variable magnitude and sign are observed along the curve-shaped thrust fronts. Rotations are virtually absent at both end points of the arc. Moving toward the apex, progressively greater counterclockwise (CCW) and clockwise (CW) rotations occur along the E-W and N-S fronts, respectively. The rotations increase continuously and more than linearly, reaching their maximum values (∼80° CCW and ∼50° CW) around the apex. Here, the more strongly CCW and CW rotated fronts are separated by a domain characterized by local block rotations. The inequality between the maximum CCW and CW rotation values is likely a consequence of the asymmetry of the indenter displacement direction (N70°E) with respect to the preorogenic trends of its margins (E-W and N-S). From an oroclinal point of view, the fronts close to the end points virtually define a nonrotating arc, while the pattern around the apex is similar to that of an orocline. We conclude that close to end points, nonrotational thrusting normal to the indenter margins occurred, while in the vicinity of the apex, the peritidal carbonates acted as an “ice breaker”, pushing apart (and strongly rotating) the weaker multilayer located ahead.