Paleomagnetism of the Acatlan terrane, southern Mexico: evidence for terrane rotation

Abstract

232 drill samples were collected from 33 sites from the Acatlan Terrane, southern Mexico. The medium-grade metamorphosed basement rocks (schists, granitoid, greenstones) showed magnetic directions that are randomly distributed and no meaningful results could be obtained. However, late Paleozoic red beds, the Ordovician (?) Totoltepec Granite and the early Paleozoic (?) Tecomate Limestone (metamorphosed in Acadian times) give coherent paleomagnetic directions. The samples responded well to thermal demagnetization but not to alternating field demagnetization. The ages of the magnetizations are reasonably bracketed between Carboniferous and Jurassic. Compared with data from the North American craton and from the Oaxaca terrane, conclusive evidence for major north-south displacements of the Acatlan terrane is not present, but significant clockwise rotations of the terrane with respect to the craton and the adjacent Oaxaca terrane are quite evident. These rotations occurred during the Jurassic or Early Cretaceous.