Paleomagnetic study of an arcuate fold belt developed on a marginal orogen: The Cajamarca deflection, northern Peru

A paleomagnetic study of over 500 cores from 48 sites sampled in Albian to Turonian sedimentary formations along the Cajamarca deflection in northern Peru indicates that these lithologies carry a stable remanent magnetization. In the two major segments of the deflection, positive fold tests establish that the magnetization predates the folding, except for five sites in the western part which appear to be remagnetized by the intrusion of Paleocene granites. The eastern part of the deflection does not appear to have undergone any significant rotation, whilst a post-late Eocene counterclockwise rotation of about 25° is recorded in the central and western parts. This angular difference only accounts for about half of the difference in the strikes of structures in the two sections of the deflection. When considered with the available tectonic, sedimentological and geodynamic data, these results indicate that the arcuate shape of the Cajamarca fold belt results from complex processes. Early multi-phased compressional events of Paleocene-Eocene age created the folds and built an arcuate structure with non-rotational mechanisms. Then, in post-late-Eocene times the structure reached its present form after rotation of its central and western parts. The bearing of these results on the geodynamic evolution of the Andean Cordillera is discussed.