THE RÍO DE LA PLATA CRATON AND THE ASSEMBLY OF SW GONDWANA.

RAPELA, C.W.; PANKHURST, R.J.; CASQUET , C.; FANNING, C.M.; BALDO, E.; GONZÁLEZ CASADO, J.; GALINDO, C.; DAHLQUIST, J.

EARTH-SCIENCE REVIEWS

Elsevier B.V.

Año: 2007 vol. 83 p. 49 - 82

0012-8252

The extent and nature of the early Palaeoproterozoic craton of Rio de la Plata of southern South America, a major but poorly understood crustal component in Neoproterozoic plate reconstructions, as well as the depositional, metamorphic and magmatic history of the surrounding orogenic belts, are reviewed and reassessed, in part through the analysis of material recovered from deep boreholes in western Argentina that penetrated Palaeozoic cover into basement. U–Pb SHRIMP zircon ages for these samples of 2162 ( 6 Ma (diorite), 2189 ( 14 Ma (amphibolitic schist) and 2088 ( 6 Ma (granite) encompass the range of ages determined for the major orogenic events in the exposed parts of the craton close to the Atlantic coasts of Uruguay and Argentina. Taken together with the geochemical and Nd-isotope characteristics of these samples and an olivine gabbro from a further borehole that failed to yield zircon, these result strongly suggest that the Rio de la Plata craton is extremely uniform in its dominant chrono-tectonic and lithological make-up, and that it extends westwards as far as the 535–520 Ma Pampean orogenic belt, against which it probably has a fault contact.    U–Pb SHRIMP zircon detrital age patterns are presented for representative metasedimentary samples from the craton cover in the Tandilia belt of eastern Argentina, and from the Pampean (Cambrian) and Famatinian (Ordovician) belts to the west of the craton. Whereas the oldest cover rocks in Tandilia clearly show material derived from the underlying craton, such detritus only appears in the younger (Ordovician) units to the west. Sedimentary protoliths in the Pampean belt were dominated by Neoproterozoic (broadly ~600 Ma) and late Mesoproterozoic (broadly ~1100 Ma) provenance, and derivation from the Rio de la Plata craton is impossible. Regional considerations, including previously published zircon data, palaeocurrent and structural data, suggest that these rocks must have had an origin within Gondwana, for which the closest identifiable sources are ‘Brazilian’ and ‘African (Namaqua–Natal)’. Consequently, the preferred model for the Pampean orogeny, is one in which the Rio de la Plata craton was an exotic crustal plate; it was inserted tectonically, by large-scale strike-slip movement from the north (present-day sense), between the Neoproterozoic Brasiliano arc and fore-arc sequences that had developed on the western margin of the Kalahari craton.