PALEOMAGNETIC CONFIRMATION OF THE LAURENTIAN ORIGIN OF THE ARGENTINE PRECORDILLERA

Several recent tectonic models have portrayed the Argentine Precordill era has been recently portrayed as an Early Paleozoic Laurentian deriv ed exotic terrane now found in southwestern South America. These model s have primarily been based on strong biogeographic and stratigraphic evidence, however, no paleomagnetic data have previously been availabl e to independently test them. A paleomagnetic study was, therefore, ca rried out on the Early Cambrian Cerro Totora Formation, exposed in the northern reaches of the Argentine Precordillera. After stepwise therm al demagnetization a pre-folding remanence was identified in ten sites of this formation, yielding a paleomagnetic pole (CT) at 37.0 degrees N, 314.1 degrees E, A(95) = 5.8 degrees. This pole is not consistent with the latest Proterozoic-Early Paleozoic apparent polar wander path for Gondwana, but it agrees with the Early Cambrian Section of the La urentian path if the Argentine Precordillera is positioned as the conj ugate margin of the Ouachita embayment in southeast Laurentia. This re sult confirms that the Precordillera is an allochthonous terrane deriv ed from Laurentia in Cambrian times, that was later accreted to Gondwa na, probably in Middle Ordovician times. (C) 1998 Elsevier Science B.V .