Bending of the Bolivian orocline and growth of the central Andean plateau: Paleomagnetic and structural constraints from the Eastern Cordillera (22-24°S, NW Argentina)

We report new paleomagnetic and structural data from late Cretaceous to Mio-Pliocene continental sandy/silty sedimentary rocks from the Eastern Cordillera (central Andes). Here, N–S to NNE– SSW ridges hosting Paleozoic basement and upper Cretaceous continental red beds overthrust thick adjacent Cenozoic basins. Pretilting (and likely primary) reliable directions gathered at 15 sites document 45.9 ± 9.4, 30.1 ± 23.9, and 15.4 ± 19.3 clockwise (CW) rotations with respect to South America occurring after the late Cretaceous (80 Ma), Oligo-Miocene (20–30 Ma), and late Miocene- Pliocene (5–10 Ma), respectively. Conversely, four upper Cretaceous sites from the walls of a N–S leftlateral strike-slip fault (Yavi–Abra Pampa fault) yield a null rotation. About 20 km to the west, flower structures and subvertical syntectonic strata dated at 14.26 ± 0.19 Ma are exposed along the subparallel Abra Moreta left-lateral strike-slip fault. Relying on data from the literature on the period when deformation began, we suggest that since Eo- Oligocene times (30–40 Ma) the Eastern Cordillera has undergone a regional CW rotation of 40–50, synchronous with crustal shortening and large-scale bending of the Andean salient. The CW rotation is possibly still active today, as documented by regional GPS data from the Andes. Since 15 Ma ago, the activity of N–S left-lateral strike-slip faults induced counterclockwise rotations along the fault zone, locally annulling the regional CW rotation. In agreement with a previous model, we speculate that mid-Miocene strike-slip activity accommodated the progressive southward spreading of the Altiplano- Puna high-altitude plateau, laterally migrating from the overthickened crustal region of the salient apex.