Structures observed in a 1000 km2 area of Grenville age Precambrian metasediments near Oaxaca in southern Mexico record the effects of a single orogenic event that produced cylindroidal folds about axes with an average bearing of N. 32° W. and plunge of 26° NW. The orientation of this structural grain appears to provide support for previous proposals (based on geochronology) that a structural belt of Grenville age rocks extends southward from Texas into the Oaxaca area. Further interpretations based on these trends suggest that the Pacific boundary of the Oaxacan Precambrian terrane resulted from continental fragmentation and that adjustments associated with opening of the Gulf of Mexico have not reoriented significantly the Oaxaca area.

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