Provenance of the late Proterozoic to early Cambrian metaclastic sediments of the Sierra de San Luis (Eastern Sierras Pampeanas) and Cordillera Oriental, Argentina

Abstract

Provenance studies have been performed utilising major and trace elements, Nd systematics, whole rock Pb–Pb isotopes and zircon U/Pb SHRIMP data on metasedimentary rocks of the Sierra de San Luis (Nogolí Metamorphic Complex, Pringles Metamorphic Complex, Conlara Metamorphic Complex and San Luis Formation) and the Puncoviscana Formation of the Cordillera Oriental. The goal was the characterisation of the different domains in the study area and to give insights to the location of the source rocks. An active continental margin setting with typical composition of the upper continental crust is depicted for all the complexes using major and trace elements. The Pringles Metamorphic Complex shows indications for crustal recycling, pointing to a bimodal provenance. Major volcanic input has to be rejected due to Th/Sc, Y/Ni and Cr/V ratios for all units. The εNd(540 Ma) data is lower for the San Luis Formation and higher for the Conlara Metamorphic Complex, as compared to the other units, in which a good consistency is given. This is similar to the TDM ages, where the metapsammitic samples of the San Luis Formation are slightly older. The spread of data is largest for the Pringles Metamorphic Complex, again implying two different sources. The whole rock 207Pb/206Pb isotopic data lies in between the South American and African sources, excluding Laurentian provenances. The whole rock Pb–Pb data is almost indistinguishable in the different investigated domains. Only the PMC shows slightly elevated 208Pb/204Pb values. Possible source rocks for the different domains could be the Quebrada Choja in the Central Arequipa–Antofalla domain, the Southern domain of the Arequipa–Antofalla basement, the Brazilian shield or southern Africa. Zircon SHRIMP data point to a connection between the Puncoviscana Formation and the Conlara Metamorphic Complex. Two maxima around 600 Ma and around 1000 Ma have been determined. The Nogolí Metamorphic Complex and the Pringles Metamorphic Complex show one peak of detrital zircons around 550 Ma, and only a few grains are older than 700 Ma. The detrital zircon ages for the San Luis Formation show age ranges between 590 and 550 Ma. A common basin can be assumed for the Conlara Metamorphic Complex and the Puncoviscana Formation, but the available data support different sources for the rest of the Complexes of the Sierra de San Luis. These share the diminished importance or the lack of the Grenvillian detrital peak, a common feature for the late Cambrian–early Ordovician basins of the Eastern Sierras Pampeanas, in contrast to the Sierras de Córdoba, the PVF and the Conlara Metamorphic Complex.