Laurent Aubry

Paleomagnetic study along the southeastern edge of the Altiplano - Puna Plateau: Neogene tectonic rotations

In northwestern Argentina the transition zone between the Puna and the Sierras Pampeanas was deformed in Late Miocene and Pliocene time. Structural observations suggest that local clockwise block rotations might be observed associated with dextral transpression. This study contributes new paleomagnetic results from four sites in Cretaceous rocks and 19 sites in Neogene sedimentary sequences. When compared with reference paleomagnetic data for stable continental South America, the results show an average inclination shallowing error of 10.5° and a pattern of clockwise rotations up to 29°. Study of the anisotropy of magnetic susceptibility (AMS) on 278 specimens provided, for most sites, AMS tensors with an oblate shape controlled by sedimentation and compaction, explaining the observed inclination shallowing. A slight AMS lineation was measured and we argue that this magnetic lineation reflects Late Miocene-Pliocene compression. A correlation observed between magnetic lineations, deduced from the AMS analysis, and rotation estimates from remanent magnetizations, demonstrates that the inferred shortening directions have also been rotated clockwise.