Using anisotropy of magnetic susceptibility to better constrain the tilt correction in paleomagnetism: A case study from southern Peru

International audience[1] We report a combined study of anisotropy of low field magnetic susceptibility (AMS) and paleo-magnetism from 16 sites in a sedimentary sequence of Eocene–early Oligocene red beds in southern Peru. Incipient tectonic strain is recorded during the early stages of deformation. Nonhorizontal magnetic linea-tion in geographic coordinate suggests either non-cylindrical folding and/or interference of two phases of compressive deformation and tectonic rotation. Applying the classic tilt correction results in significant dispersion in paleomagnetic declinations and apparent clockwise and counterclockwise relative tectonic rota-tions. A dispersion in the orientation of the magnetic lineation also arises from a simple classic tilt correction inducing apparent local rotation in paleostress determi-nation. The magnetic lineation is a good proxy to detect a complex history of folding when the finite strain is not large enough to reset the magnetic fabric acquired during the early stages of deformation and when detailed geo-logical field mapping is not available or not possible. In the present study, a double correction rotating first the lineation to the horizontal reduces significantly the dis-persion of the paleomagnetic data with respect to con-ventional tilt correction (Fisher parameter k increases from 14 to 35). The interest of this double correction must obviously be evaluated for each study according to the complexity of the folding and the intensity of the deformation. Assuming a mean age of 40 Ma for the sedimentary sequence, no significant rotation (−4.5° ± 8.4) is observed in this area of the Peruvian Andes. Citation: Roperch, P., V. Carlotto, and A. Chauvin (2010), Using anisotropy of magnetic susceptibility to better constrain the tilt correction in paleomagnetism: A case study from southern Peru, Tectonics, 29, TC6005