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. Str uctural observations suggest that local clockwise block rotations migh t be observed associated with dextral transpression. This study contri butes new paleomagnetic results from four sites in Cretaceous rocks an d 19 sites in Neogene sedimentary sequences; When compared with refere nce paleomagnetic data for stable continental South America, the resul ts show an average inclination shallowing error of 10.5 degrees and a pattern of clockwise rotations up to 29 degrees. Study of the anisotro py of magnetic susceptibility (AMS) on 278 specimens provided, for mos t sites, AMS tensors with an oblate shape controlled by sedimentation and compaction, explaining the observed inclination shallowing. A slig ht AMS lineation was measured and we argue that this magnetic lineatio n reflects Late Miocene-Pliocene compression. A correlation observed b etween magnetic lineations, deduced from the AMS analysis, and rotatio n estimates from remanent magnetizations, demonstrates that the inferr ed shortening directions have also been rotated clockwise.