Zircon and titanite U-PbSHRIMP geochronology of Neoproterozoic felsic magmatism on the eastern border of the Rio de la Plata Craton, Uruguay

The Neoproterozoic reactivation of the eastern border of the Rio de la Plata Craton in Uruguay has major significance in the Precambrian geology of South America because it occurred on the southernmost extension of the 4000 km long Brasiliano cycle belt. The reactivated belt is, known to be mostly Neoproterozoic in age, but three major geological events are dated for the first time in this investigation by the sensitive, high-mass resolution ion microprobe (SHRIMP 11). The syntectonic Rocha syenogranite intruded the Cuchilla Dionisio Terrane at 762 +/- 8 Ma, within the time span of the Sao Gabriel orogeny of the Brasiliano cycle. The Puntas del Santa Lucia monzogranite intruded the Nico Perez Terrane at 633 +/- 8 Ma, during the Dom Feliciano orogeny, which is the main thermal peak of the Brasiliano cycle in South America. This monzogranite was metamorphosed at 607 +/- 7 Ma. The Cerro Aguirre dacite, a volcanic rock from the Piriapolis foreland basin, crystallized at 571 +/- 8 Ma during one of the latest events of the Brasiliano cycle. Inherited zircon cores from the Rocha syenogranite yielded ages near 2.0 Ga, a possible indication of Paleoproterozoic basement in the terrane. (C) 2002 Elsevier Science Ltd. All rights reserved.