Abstract

The mean direction of remanent magnetization in well-dated, structurally and petrologically simple Cretaceous ash-flow tuffs from the central valley of Chile, near Santiago, indicates that the region has undergone a small (about 14°) clockwise rotation. Two other paleomagnetic studies on Cretaceous rocks from coastal Chile give a similar result. We tentatively attribute these rotations to dextral shear caused by oblique subduction of the Nazca plate beneath South America. In contrast, Cretaceous rocks from Peru seem from paleomagnetic evidence to have been rotated counterclockwise relative to the stable interior of the continent. This sense of apparent rotation agrees with the sense of deflection of geologic trends from north-south to north-northwest at about the Peru-Chile border (the Arica deflection). On the basis of these observations, several authors have suggested that the Arica deflection is an orocline. However, uncertainty in all such paleomagnetic interpretations is introduced by what seems to be a very streaked distribution of Cretaceous reference poles from the South American craton. The cause of this streaking is not known.

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