Clockwise block rotations along the eastern border of the Cordillera de Domeyko, Northern Chile (22 degrees 45 '-23 degrees 30 ' S)

We report new paleomagnetic results from a study of 38 sites in Cretaceous to Early Tertiary red beds and volcanic rocks belonging to the Purilactis G roup, which outcrop along the western border of the Salar de Atacama Basin. After detailed thermal demagnetization, characteristic directions were det ermined for 32 units. In most cases, red bed sediments from the lower membe rs of the Purilactis Group have a well-defined normal polarity magnetizatio n probably carried by hematite forming an early diagenetic cement. A large decrease in the dispersion of the paleomagnetic directions upon tilt correc tion demonstrates that this magnetization is a pre-tectonic magnetization. We interpret the dominant occurrence of the normal polarity direction as ev idence for acquisition of the magnetization during the Cretaceous normal po larity superchron. Large deviations of the paleomagnetic declinations from the expected ones for stable South America provides new evidence for clockw ise tectonic rotations associated with Tertiary deformation in the Cordille ra de Domeyko. These data confirm that clockwise tectonic rotations are one of the most significant structural characteristics of the north Chilean An des. This study, however, indicates spatial variation in the magnitude of t he rotation with rotations >60 degrees in the Cerro Totola area. These rota tions have occurred in conjunction with transpressional deformation that af fected large tracts of the Cordillera de Domeyko during Eocene deformation. The systematic observation of clockwise rotations contemporaneous with sin istral displacements in the Cordillera de Domeyko can be explained by shear -traction at the base of the brittle crust. (C) 2000 Elsevier Science B.V. All rights reserved.