Uranium-lead dating of felsic magmatic cycles in the southern Sierras Pampeanas, Argentina

Abstract

Uranium-lead ion probe dating of zircons from granites of the southern Sierras Pampeanas, Argentina, has provided new constraints on the timing of major felsic magmatic events and tectonic development of the proto-Andean Gondwana margin. The zircon data indicate that there were three separate episodes of granite emplacement in the southern Sierras Pampeanas. The cycles, occurring during the Cambrian (ca. 530-510 Ma), Early Ordovician (ca. 490-470 Ma), and Devonian (ca. 403-382 Ma), are referred to as the Pampean, Famatinian, and Achalian Cycles, respectively. There is no evidence to support Late Ordovician or Silurian granite intrusion, as indicated in previous Rb-Sr and K-Ar isotopic age data. The revised Early Ordovician age of the Famatinian Cycle indicates that final amalgamation of the Precordillera had taken place prior to 470 Ma, rather than by about 450 Ma as previously suggested. Show more