The African provenence of southern South America terranes: A record from Rodinia break-up to Gondwana assembly.

RAPELA, CARLOS W.; FANNING, C. MARK; CASQUET, CESAR; PANKHURST, ROBERT J.; SPALLETTI, LUIS; POIRÉ, DANIEL G.; BALDO, EDGARDO

Mar del Plata

Congreso; GEOSUR 2010 - International Symposium on the Geology and Geophysics of the Southern Hemisphere; 2010

Istituto Nazionale di Oceanografia e di Geofisica Sperimentale

A remarkable characteristic of southern South America, is that the 2.26-2.02 Ga Palaeoproterozoic sequences of the Río de la Plata craton that define the oldest southern core of the continent, have not been affected by the widespread Neoproterozoic deformation and magmatism associated with the assemblage of Gondwana.  In Uruguay, the Sarandí del Yi megashear separates the Paleoproterozoic basement unaffected by Neoproterozoic events  (Piedra Alta and Pando terranes), from the complex  Archean to Mesoproterozoic Nico Pérez terrane, which was reworked during the Mesoproterozoic (Bossi & Cingolani 2009,  Oyhantçabal et al., 2009 and references therein), as well as the collage of terranes accreted during the Brasiliano-Panafrican orogeny (e.g., Punta del Este terrane and Dom Feliciano belt). Further south in the Tandilia belt in Argentina, SHRIMP analyses of the 2.23-2.06 Ga Paleoproterozoic basement do not show a Neoproterozoic overprint (Hartmann et al., 2002b); the 2.19-2.09  Ga  samples recovered from deep drill cores in the western side of the craton also show no such evidence (Rapela et al., 2007).  It is difficult to make a coherent scenario incorporating the several geodynamic models recently proposed for the pre-Atlantic Adamastor ocean (e.g. Goscombe et al., 2005; Saalmann et al., 2007; Basei et al., 2008; Gray et al., 2008; Oyhantçabal et al., 2009), and those for the western side of the Río de la Plata craton (Rapela et al., 2007; Drobe et al., 2009, Siegesmund et al., 2009). Another important  issue that remains poorly explained is the relative position of the Kalahari, Congo and Río de la Plata cratons during the early Neoproterozoic.  This paper presents new U-Pb SHRIMP results on drill core samples from close to the present Atlantic coast,  at the tip of the Tandilia belt on the eastern margin of the Río de la Plata craton (Punta Mogotes). Zircon provenance patterns on these critically located samples, together with previous results, allow an interpretation of the Neoproterozoic rifting-drifting of the Río de la Plata craton,  and infer a close connection with the southwestern Congo Craton.  The whole  process covers the transition from Rodinia dispersal to Gondwana assembly.