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

Cambrian to Early Ordovician carbonate deposits from the eastern and central areas of the Argentine Precordillera have been studied palaeomagnetically in six different localities (21 sites). Three localities (11 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 with higher coercivities and unblocking temperatures (component B). Component A is interpreted as a Recent or possibly Neogene secondary magnetization and component B as Permian. IRM studies show that the magnetization is carried by probably SD or PSD magnetite. The geographical distribution of the Permian remagnetization in the limestones and the occurrence of other formations remagnetized syntectonically at approximately the same time in the Western Precordillera indicate a regional remagnetization event during the Early Permian, probably associated with the San Rafaelic tectonic phase that affected the Central Chilean-Argentine 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-defined, magnetization (component C) could be isolated in three sites. VGPs computed from these sites are broadly consistent with early Palaeozoic poles of Gondwana.