EarthRef.org Reference Database (ERR) -- Arriagada et al. 2003

For the Central Valley of northern Chile (Antofagasta region), a paleomagnetic analysis of data from 108 sites, mainly in Mesozoic and Paleogene volcanic rocks, has yielded stable remanent magnetization directions for 86 sites. From these data, we infer clockwise tectonic rotations of up to 65¿ within the forearc domain of the central Andes. The apparent relationship between tectonic rotations and structural trends suggests that rotations occurred mainly during the Incaic orogenic event of Eocene--early Oligocene age. A few paleomagnetic results obtained in Neogene rocks do not show evidence of clockwise rotations. Hence the development of the Bolivian orocline during late Neogene time cannot be explained by simple bending of the whole margin. These results demonstrate that tectonic rotations within the forearc and pre-Cordillera are key elements of early Andean deformation, which should be taken into account by kinematic models of mountain building in the central Andes. For the Central Valley of northern Chile (Antofagasta region), a paleomagnetic analysis of data from 108 sites, mainly in Mesozoic and Paleogene volcanic rocks, has yielded stable remanent magnetization directions for 86 sites. From these data, we infer clockwise tectonic rotations of up to 65¿ within the forearc domain of the central Andes. The apparent relationship between tectonic rotations and structural trends suggests that rotations occurred mainly during the Incaic orogenic event of Eocene--early Oligocene age. A few paleomagnetic results obtained in Neogene rocks do not show evidence of clockwise rotations. Hence the development of the Bolivian orocline during late Neogene time cannot be explained by simple bending of the whole margin. These results demonstrate that tectonic rotations within the forearc and pre-Cordillera are key elements of early Andean deformation, which should be taken into account by kinematic models of mountain building in the central Andes.