Provenance History in Lower to Middle Paleozoic Clastic Sequences from Cuyania, Sierra de La Ventana and North Patagonian Massif, Argentina: Implications in Sw Gondwana Evolution

CINGOLANI CARLOS A.; URIZ NORBERTO J.; ABRE PAULINA; MANASSERO MARCELO

Buzios

Congreso; GONDWANA 14 ?Reuniting Gondwana: the East meets the West?; 2011

GONDWANA 14

A combination of petrography, geochemistry, Nd and Pb isotopes (whole rocks) and U-Pb and Lu-Hf on detrital zircons provide constraints to the provenance of Middle Ordovician to Devonian clastic sequences of the Cuyania terrane, Sierra de la Ventana System and North Patagonian Massif, in western-central Argentina as an essential part of the du Toit´s ´Gondwanides´. In the Cuyania terrane the uniformity shown by the provenance proxies indicate that there were no important changes within Late Ordovician to Silurian units (Abre et al., 2008). A dominant upper crustal component is evident as well as a subordinate mafic input. Detrital zircon dating further constrains the sources as being dominantly of Mesoproterozoic age, but with contributions from Ordovician, Cambrian, Neo-Palaeoproterozoic sources. Different provenance approaches indicates that the Mesoproterozoic Cuyanian basement and partially the Western Pampeanas Ranges were the main sources. The accretion of the Cuyania terrane to the proto-Andean margin of Gondwana probably occurred during Middle to early Upper Ordovician. In the Sierra de la Ventana system (Buenos Aires Province) the studied units were Napostá, Providencia and Lolén Formations and in the North Patagonian Massif was the Sierra Grande Formation. All these clastic units show similar stratigraphical characteristics developed in a shallow marine platform environment and assigned to the Silurian-Devonian times. The sedimentary provenance analysis based on petrography and whole rock geochemistry and U-Pb and Lu-Hf isotope data on detrital zircons shown upper continental crust contribution with the main sedimentary sources from Cambrian-Ordovician and Neoproterozoic age, while a secondary mode is Mesoproterozoic (Uriz et al., 2011). The studied samples from the Lolén Formation show a change in the sedimentary provenance, with a main frequency of Mesoproterozoic detrital zircons. Sources are from Famatinian, Pampean-Brasiliano, Mesoproterozoic to Paleoproterozoic cycles. For both regions the obtained Nd TDM model ages were mainly from Mesoproterozoic to Paleoproterozoic as an average of sedimentary sources. The εHf (t) data show juvenile (31%), recycled (64%) and crustal (5%) origins for the studied zircon grains. The Lolén Formation studied samples of the upper part of the Ventana Group shows a different U?Pb age pattern compared with all other samples. It shows mainly Late Famatinian and Mesoproterozoic detrital zircon clusters and the presence of Neoproterozoic and Paleoproterozoic zircon ages as secondary peaks. This indicates that important changes regarding tectonic history of the depocenter during Middle-Upper Devonian occur. A few contributions from Archean to Paleoproterozoic sources were found. This means that the Río de la Plata/Kaapval cratons were not a main source for detritus input to these basins during Silurian?Devonian times. Detrital zircon patterns of Sierra de la Ventana and North Patagonian Massif suggest that the detritus were derived from Gondwanan sources and from terranes accreted during the Pampean (Brasiliano?Pan-African) and Famatinian orogenic cycles. We discuss the implications of these data in the paleogeographic evolution models on SW Gondwana during Lower to Middle Paleozoic.