MULTIPLE MAGNETIZATIONS IN THE CAMBRIAN-ORDOVICIAN CARBONATE PLATFORMOF THE ARGENTINE PRECORDILLERA AND THEIR TECTONIC IMPLICATIONS

Cambrian to Early Ordovician carbonate deposits from the eastern and c entral areas of the Argentine Precordillera have been studied palaeoma gnetically in six different localities (21 sites). Three localities (1 1 sites) in the Central Precordillera show two post-tectonic magnetic components: a shallow up- and northward-directed component removed by intermediate AF, up to 20 mT, and at temperatures up to 450-degrees-C (component A); and a steeper down- and southward-directed component wi th higher coercivities and unblocking temperatures (component B). Comp onent A is interpreted as a Recent or possibly Neogene secondary magne tization and component B as Permian. IRM studies show that the magneti zation is carried by probably SD or PSD magnetite. The geographical di stribution of the Permian remagnetization in the limestones and the oc currence of other formations remagnetized syntectonically at approxima tely the same time in the Western Precordillera indicate a regional re magnetization event during the Early Permian, probably associated with the San Rafaelic tectonic phase that affected the Central Chilean-Arg entine Andes in the late Palaeozoic (290-265 Ma aprox.). Eastern areas of the Precordillera not affected by this event do not show evidence of this Permian remagnetization and a probably primary, albeit ill-def ined, magnetization (component C) could be isolated in three sites. VG Ps computed from these sites are broadly consistent with early Palaeoz oic poles of Gondwana.