Paleomagnetic tracking of mountain building in the Peruvian Andes since 10 Ma

Abstract

We report paleomagnetic data from 73 sites (628 samples) of upper Oligocene to Pliocene rocks from central and northern Peru. The data indicate that the Subandean Zone has not experienced vertical axis rotation since the upper Oligocene, whereas the coast and the Western Cordillera record a coherent pattern of counterclockwise rotations emplaced in the last 10 Ma. This pattern can best be explained by two competing hypotheses: (1) a propagation in rotations from the Bolivian Orocline toward the north or (2) a more punctual and widespread event linked to subduction of the Nazca Ridge that caused the rotations. On the basis of the time-space relationship of paleomagnetic rotations, deformation, magmatism and Nazca-South America plate convergence, the latter appears more likely. Moreover, because the rotations north of the Abancay deflection (~15.5°S) are synchronous with deformation and exhumation, they indicate that major mountain building in the Peruvian Andes has occurred since 10 Ma. Finally, we suggest that a succession of aseismic ridge subduction events played an important role in shaping the modern topography of the Andean chain.