Preliminary results: paleomagnetism of mesozoic units from northwest Sonora and their tectonic implication for northern México

Abstract

Preliminary results from a paleomagnetic investigation of Upper Triassic-Lower Jurassic miogeosynclinal strata (Antimonio Formation) located in northwest Sonora, Mexico yield a paleomagnetic pole position at 74.8°N y 106.2°E (I =33.8°, D = 350.0, α95 = 12.1°, k = 104.4, dp =7.89 y dm = 11.68). This pole position agrees well with a pole determined from an earlier study of the Upper Triassic-Lower Jurassic Nazas Formation (Nairn, 1976) of north-central Mexico. The relative position of northern Mexico and North America prior to and during the breakup of Pangaea have been speculated on by many previous workers. Our data in combination with those of Nairn (1976) suggest that if differential movement of northern Mexico relative to North America has occurred since the early Mesozoic, displacement of a segment of the northern Mexico apparent polar wandering path is of a small order and in a counterclockwise direction with respect to the North American apparent polar wandering path. The motion of the northern Mexico tectonic block relative to cratonic North America is limited to, at most, several hundreds of kilometers displacement which must be of a sinistral sense.