Proterozoic-Early Paleozoic evolution in western South America -: a discussion

The hypothesis of exotic terranes in Peru, Bolivia, Argentina and Chile generated discussions on the mode of transfer and extent of accretional events that may have occurred in the southern Andes during the Late Proterozoic-Early Paleozoic. Initially, a tectogenesis based on autochthonous mobile fold belts was discussed. Following ideas emphasised the fragmentation of the supercontinent Rodinia, Laurentia moving along the West Gondwana border and colliding with the Gondwana western margin. The most important effect of this Laurentia/Gondwana relationship was attributed to the Argentine Precordillera. (or Cuyania) terrane splitting off from Laurentia and docking to Gondwana in the Early Paleozoic. In this study, the most cited arguments for this Laurentia/Precordillera relationship are discussed, emphasising paleontological considerations. It is shown that these arguments do not exclude a close original vicinity of the Precordillera terrane to Gondwana. The Precordillera terrane is suggested to be part of a hypothetical platform, which developed between South America, Africa and Antarctica (SAFRAN platform), and which was displaced to its actual position by transcurrent faults. The collisional events in the Sierras Pampeanas ensued from strike-slip movements and were responsible for the S and I type transpressional magmatism along the Pampean and Famatinian terranes. The final result of this continent-parallel movement of terrane slices is similar to that of a terrane split off from Laurentia, but the first-named way of formation easier explains the general continuity of plate convergence at the western border of Gondwana than the Laurentia/Precordillera connection does. (C) 2002 Elsevier Science B.V. All rights reserved.