Paleomagnetismo de rocas jurásicas del norte de Oaxaca y sus implicaciones tectónicas

Abstract

We report paleomagnetic results for the Jurassic Formations of Yucuñuti and Caliza con Cidaris. The Formations have been studied in the arcas ofTezoatlan and Tlaxiaco, Oaxaca State, respectively. The region lays within the Mixteca Terrane which presents tectonic and stratigraphic rel.ations indicative of tectonic movements at various times during its history. During most of the Middle Jurassic-to-Neocomian interval, the Mixteca Terrane experienced subsidence in a tensional tectonic regime. The process resulted in the deposition of a thick fluvialchanging-to-marine sedimentary sequence. Paleogeographic and paleobiogeographic relationships suggest a Pacific conexion for the Mixteca Terrane. Field and laboratory tests for the age of acquisition of the magnetic remanence suggest that the formations may retain a Jurassic direction. The mean direction for the Callovian Yucuiluti Formation is N= 32, Dec= 328.6°, lnc= 34.8°, k= 66 and 95 = 15°; and that for the Oxfordian Caliza con Cidaris is N = 92, Dec = 12.8°, Inc. = 38.1 °, k= 83 and 95=7°. The paleomagnetíc record for the formations differs from that expected from the corresponding data reported for cratonic North America. The angular divergences if associated to tectonic movements indicate a northward latitudinal movement and a counterclockwise 18° y 30° degrees rotation. The tectonic movement may have occurred at sorne time between the Oxfordian and the Albian.