Paleomagnetic constraints on the tectonic evolution of Paleozoic suspect terranes from southern South America.

RAPALINI, AUGUSTO E.; ASTINI, RICARDO A.; CONTI, CARLOS M.

Laurentia - Gondwana connections before Pangea, Geological Society of America, Special Paper, 336

Geological Society of America

Lugar: Boulder, Colorado; Año: 1999; p. 171 - 182

Abstract               The Paleozoic evolution of southwestern Gondwana apparently involved the accretion of several large suspect terranes at different times and under different tectonic circumstances. The recent acquisition of paleomagnetic data from Paleozoic rocks of this region, albeit still scarce, permit establishment of some constrains on the tectonic and paleogeographic evolution of some of these terranes.   A reliable paleomagnetic pole from the Early Cambrian Cerro Totora Formation in northern Precordillera confirms that the Argentine Precordillera is an exotic terrane that was part of or adjacent to Laurentia, very likely at the Ouachita Embayment, in the Early Cambrian.  Paleomagnetic poles an Early Ordovician magmatic belt in NW Argentina permit the identification of a peri-Gondwanic rotated terrane called the “Eastern Puna - Famatina” with volcanic arc affinities.  Early Paleozoic paleomagnetic poles from the Western Puna (Sierra de Almeida, Chile) were previously interpreted as evidence of a para-autochthonous nature of the Arequipa-Antofalla Massif that rotated successively clockwise and counterclockwise.  New preliminary paleomagnetic data in the same region (Salar del Rincón, Argentina) are not easily reconciled with the previous data, unless a Late Ordovician pre-tectonic remagnetization is assumed for the latter. The paleomagnetic and geologic data permit an alternative interpretation based on the fact that the Arequipa and Antofalla blocks can be considered as different terranes.  In this case the paleomagnetic data obtained so far is representative of the Antofalla block alone and suggests at least 1000 km latitudinal displacement of this block with respect to its present position in the South American margin for the Late Cambrian - Early Ordovician.  Accretion of this terrane to the Gondwana margin must have occurred in latest Ordovician.   Paleozoic paleomagnetic poles from Patagonia indicate that this terrane shares a common APWP with Gondwana since the Early Devonian.  This suggests that no significant movement occurred between these two crustal blocks since that time.  Many questions regarding the complex tectonic evolution of  southwestern South America, that can potentially be addressed by paleomagnetism remain unanswered.