HR: 0800h
AN: GP31C-01    [Abstracts]
TI: Tectonic Implications of Widespread Remagnetization of Late Proterozoic Sedimentary Units in Uruguay
AU: * Sanchez Bettucci, L
EM: leda@fcien.edu.uy
AF: Departamento de Geologia, Facultad de Ciencias, UdelaR, Igua 4225, Montevideo, 11400, Uruguay
AU: Rapalini, A
EM: rapalini@gl.fcen.uba.ar
AF: INGEODAV, Departamento de Ciencias Geologicas, FCEN, Universidad de Buenos Aires and CONICET, Ciudad Universitaria Pab. 2, C1428EHA, Buenos Aires, Argentina
AB: A paleomagnetic study was performed on three Neoproterozoic sedimentary successions exposed in Uruguay in order to better define the paleogeographic evolution of the Rio de la Plata craton prior to and during the assembly of Gondwana. These units comprise the latest Ediacaran to Early Cambrian calcareous Cerro Victoria Fm, the late Ediacaran clastic Yerbal Fm and the calcareous Polanco Fm and the Ediacaran clastic Rocha Fm. None of these carry the original remanence and they were affected by remagnetizations. The most widespread remagnetization is shown by the Cerro Victoria, Yerbal and Rocha Formations. A dual-polarity post-folding remanence, carried by hematite, was isolated in all these units. Their corresponding pole positions are virtually identical (CV: 83.4 °S, 312.8 °E, dp: 3.3 °; dm: 4.3 °; Y: 79.5 °S, 295.9 °E, dp: 5.4 °, dm: 7.0 °; R: 77.4 °S, 292.6 °E, dp: 3.5 °, dm: 4.4 °) suggesting the same magnetization age and process. Comparison with the South American path suggests the Late Permian-Early Triassic or the latest Cretaceous-Paleogene as the most likely times for its acquisition. These poles are also identical to the pole of the Late Proterozoic La Tinta Fm., which is interpreted as affected by the same remagnetization, and therefore, invalid for paleogeographic reconstructions. A different magnetic component, also dual polarity and postfolding, was defined at two sites of the Cerro Victoria Fm. and two of the Polanco Fm, possibly carried by magnetite. The mean geomagnetic poles from both units (CVc: 7.8 °N, 343.9 °E, dp: 11.1 °; dm: 15.8 °, P: 5.9 ° N, 325.3 ° E, dp: 13.7 °, dm: 16.9 °) fall on the Middle Cambrian to Early Ordovician segment of the Gondwana APWP, suggesting that age for the remagnetization. This allows us to establish the age of the tectonic event affecting the Neoproterozoic units of the RP craton as Early Cambrian (ca. 525 Ma).
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 1527 Paleomagnetism applied to geologic processes
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly