Results of paleomagnetic studies of volcanic and sedimentary rocks from Chihuahua, northern Mexico, suggest that a counterclock-wise tectonic rotation relative to “stable” North America occurred during early Tertiary time. The results permit development of a model for the tectonic evolution of southern North America, in which northern Mexico south of the Texas lineament is rotated in order to restore it to its Eocene-Oligocene position. This explains the “anomalous” zone of the Cordilleran orogenic belt between southern Nevada and northern Chihuahua, which suggests that the belt was once continuous and that the complications are the result of later tectonic events. The restoration may also explain the dislocation of the Mesozoic batholith belt of western Mexico, and the large nappe structures of the Sierra Madre Oriental within the continuation of the belt into Mexico.

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