DETRITAL-ZIRCON GEOCHRONOLOGY DEMONSTRATES COMMON PROVENANCE OF CAMBRIAN-DEVONIAN SANDSTONES OF THE CUYANIA (GREATER PRECORDILLERA) TERRANE OF WESTERN ARGENTINA AND NEOPROTEROZOIC SANDSTONES DEPOSITED ON THE RÍO DE LA PLATA CRATON OF URUGUAY AND EASTERN ARGENTINA

The Cuyania (greater Precordillera) terrane of western Argentina is considered by many to have rifted from the Ouachita embayment of Laurentia in the Early Cambrian, drifted across the Iapetus Ocean, and docked with the proto-Andean margin of Gondwana in mid to late Ordovician time. Varied stratigraphic, paleobiogeographic, geochemical, structural, and paleomagnetic evidence is cited in support. However, detrital zircon samples from Cambrian sandstones in the Precordillera, with a distinctive 600-500 Ma age population and an early Mesoprotozoic (1600-1500 Ma) population unknown in most of North America, argue against a Laurentian origin and, instead, for an origin from the southern margin of West Gondwana in the mid to late Ordovician time and subsequent migration along a transform fault. Detrital-zircon geochronology acquired recently demonstrates that the provenance of Cambrian to Devonian sandstones of Cuyania was relatively constant and stable and that a virtually identical provenance can be recognized in Neoproterozoic sandstones deposited on the Río de la Plata craton, thus further confirming the Gondwanan affinity of Cuyania.

Detrital zircon samples from 24 Cambrian to Devonian sandstones in Cuyania are dominated by a Mesoproterozoic population of 1600-1000 Ma with two prominent peaks at ~1400 Ma and ~1050 Ma. Most samples also include a conspicuous late Neoproterozoic to early Cambrian population (600-500 Ma) and several grains of varied Paleoproterozoic and Archean ages.

A detrital zircon sample from the Neoproterozoic Piedras de Afilar Formation, deposited on the Río de la Plata craton of Uruguay, has a characteristic Transamazonian age population (2100-1700 Ma), but also has a Mesoproterozoic population virtually identical to that of the samples from Cuyania. Other Neoproterozoic sandstones from Uruguay (Yerbal and Cerros San Francisco formations of the Arroyo del Soldado Group) are dominated by Paleoproterozoic and Archean populations. Given their age, these sandstones cannot include 600-500 Ma age populations, but granitoids of this age are widespread in an adjacent Brasiliano tectonic belt. Neoproterozoic sandstone samples from the Villa Mónica and Cerro Largo formations of the Sierras Bayas Group of the Tandilia region of eastern Argentina have very similar zircon-age populations.