| Summary: | A paleomagnetic study of Eocene volcanic rocks in Patagonia yields high unblocking temperature and high-coercivity magnetizations. Combining these results with those of a previous study on Patagonian Eocene basalts yields a high-precision, high-quality pole located at latitude 81°S, longitude 337.4°E, A95 = 5.7°. Critically, this paleopole is indistinguishable from that of the Late Cretaceous (circa 85-65 Ma) pole position of South America, indicating that the plate was essentially motionless with respect to the spin axis for a period of ∼45 m.y. The pole position places South America at higher (∼5°) than present-day latitudes during the Eocene, indicating that northward continental motion toward present-day latitudes must have been accomplished sometime since the late Eocene. Paleomagnetic and tectonic correlation admits the hypothesis that Cenozoic northward drift was associated with Oligocene-Miocene extension in the southern continental edge, leading to the opening of the Drake Passage, and it agrees with the timing of foredeep formation and development of fold-thrust belts in the northern continental edge. This positive correlation between the paleomagnetically predicted drift of a major continent with extension at its trailing edge and convergence at its leading edge during times for which seafloor tectonic fabric and the geological record are particularly well preserved illustrates the utility of paleomagnetism in constraining paleogeographic and tectonic reconstructions for pre-Cretaceous times. Fil: Somoza, Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina
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