The Rio de la Plata craton and the adjoining Pan-African/Brasiliano terranes: their origins and incorporation into South-West Gondwana.

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

GONDWANA RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2011 vol. 20 p. 673 - 690

1342-937X

The Neoproterozoic to Early Cambrian amalgamation of SW Gondwana through the Brasiliano/Pan-African orogeny is reviewed with emphasis on the role of the R¨ªo de la Plata craton of South America in the light of new evidence from a borehole at the eastern end of the Tandilia belt (38¡ãS). U¨CPb, Hf and O isotope data on zircon indicate that this un-reworked Palaeoproterozoic craton abuts against a distinct continental terrane to the east (Mar del Plata terrane). The craton is bounded everywhere by transcurrent faults and there is no evidence to relate it to the Neoproterozoic mobile belts now seen on either side. The Punta Mogotes Formation at the bottom of the borehole contains 740¨C840 Ma detrital zircons that are assigned to a widespread Neoproterozoic rifting event. The data suggest that the Mar del Plata terrane rifted away from the southwestern corner of the Angola block at c. 780 Ma. Negative ¦ÅHft values and ¦Ä18O N6.5¡ësuggest derivation by melting of old crust during a protracted extensional episode. Other continental terranes may have formed in a similar way in Uruguay (Nico P¨¦rez) and southeastern Brazil, where the Schist Belt of the Dom Feliciano orogenic belt is probably a correlative of the Punta Mogotes sequence, implying that the Dom Feliciano belt must extend at least as far as 38¡ãS. A new geodynamic scenario for West Gondwana assembly includes at leasttwo major oblique collisional orogenies: Kaoko¨CDom Feliciano (580¨C680 Ma) and Gariep¨CSaldania (480¨C580 Ma), the latter resulting from oblique impingement of the Rio de la Plata craton against the Kalahari craton. Assembly of this part of South-West Gondwana was accomplished before the Ordovician (to Silurian?) siliciclastic platform sediments of the Balcarce Formation in the Tandilia Belt covered the southern sector of R¨ªo de la Plata craton.