Paleomagnetic study of Jurassic and Cretaceous rocks from the Mixteca terrane (Mexico)

Three sites from Cretaceous limestone and Jurassic sandstone in northern Oaxaca, Mexico, were studied paleomagnetically. Thermal demagnetization isolated site-mean remanence directions which differ significantly ii-om the recent geomagnetic field. The paleopole for the Albian-Cenomanian Morelos formation is indistinguishable from the corresponding reference pole for stable North America. indicating tectonic stability of the Mixteca terrane since the Cretaceous. Rock magnetic properties and a positive reversal test for the Bajocian Tecomazuchil sandstone suggest that the remanence could be of primary origin, although no fold lest could be applied. The Tecomazuchil paleopole is rotated 10 degrees +/- 5 degrees clockwise and displaced 24 degrees +/- 5 degrees towards the study area, with respect to the reference pole for stable North America. Similar values were found for the Toarcien-Aalenian Rosario Formation, with 35 degrees +/- 6 degrees clockwise rotation and 33 degrees +/- 6 degrees latitudinal translation. These data support a post-Bajocian southward translation of the Mixteca terrane by around 25 degrees which was completed in mid-Cretaceous time. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.