Paleomagnetic results from Grenvillian-aged rocks from Oaxaca, Mexico: Evidence for a displaced terrane

Abstract

In order to test the possibly displaced nature of the Proterozoic (`Grenville'-aged) Oaxaca terrane, a paleomagnetic study was carried out on gneissic and meta-igneous (anorthosite) rocks with metamorphic ages reported to be between 1100 and 900 Ma. Using alternating field (AF) and thermal demagnetization techniques, we have isolated two magnetic directions: a shallow and southerly direction (D = 155[deg], I = -1[deg]) and a very steeply down direction (D = 6[deg], I = +74[deg]). It seems likely that the shallow direction is a remagnetization associated with a slight reheating and cooling due to a nearby Permian-Triassic intrusion. The steep direction is interpreted as a magnetization acquired during uplift and cooling following the Oaxacan Orogeny, and gives a paleopole at 47[deg]N, 93[deg]W with an age of ~950 Ma. This pole is at least 40[deg] from the Grenville Loop of the North American apparent polar wander path and the observed paleolatitude of 60[deg]N is much higher than that predicted for Oaxaca if it had always belonged to North America in the same relative position it has today. The high paleolatitude obtained for the Oaxaca terrane does not preclude, however, that it was part of North America during Grenvillian times, but in that case its position would have been much closer to Ontario and Quebec than it is today.