Áreas de proveniencia de meta-sedimentos e interpretación geoquímica de ambientes tectónicos de deposición de la Formación Puncoviscana: Cordillera Oriental y Sierras Pampeanas, Argentina

Abstract

“Provenance of the Puncoviscana Formation meta-sediments and geochemical interpretation of its tectonic-setting in Cordillera Oriental and Sierras Pampeanas, Argentina”. The Puncoviscana Formation sl. is an important lithostratigraphic sequence consisted of dominantly psammites and mudstones, interbedded with subordinate conglomerate, carbonates and volcanics deposited in a shallow basin between the Neo-Proterozoic and Terreneuvian on the western edge of Gondwana, which for some authors would have behaved as foreland basin and for others as a passive continental margin, a thesis we interpret like sequences of one same evolutionary process. In Puncoviscana formation sl. ichnofóssils are grouped into two associations with different distributions: an area with Nereites saltensis, which correspond to the highest levels of the Ediacaran and another one with Oldhamia radiata, which would fit on Terreneuvian levels. On another side, detrital zircons giving a wide range of ages, indicate provenances from Paleo-Proterozoic, Meso-Proterozoic and Neo-Proterozoic terranes to which are summoned those of Terreneuvian. The available radiometric values correspond to different cratonic areas recognized in the South American continent from 2,300 to 950 Ma. There are also detected zircon ages between 850 and 600 Ma, which indicate igneous activity between the end of the Sunsas and the beginning of the Pampean cycle. We propose the name of Ancajano Complex for this interval. Clastic sequences of the Puncoviscana formation, begin over the Ancajan Complex and comforms a continuous sequence from meta-sediments to Greenschists and Amphibolites metamorphic facies developed within the Pampean cycle and it ends with the Tilcaric orogeny occurred at 520 Ma, evidenced by the unconformity that separates the Puncoviscana Formation from Meson Group. The development of an extensional marginal basin between 580 and 540 Ma, led to the extrusion of basic alkaline, ultrabasic to a tholeiitic magmatism; whereas the culmination of the sedimentary sequence, and in a subduction environment, between 540 and 520 Ma, it generates significant calc-alkaline and a per-aluminous magmatism in the Eastern Cordillera and Precordillera of Catamarca, Santiago del Estero and Córdoba provinces. Geochemical analyzes on representative outcrops of different metamorphic levels, allowed us to use major, minor and trace element diagrams to characterize environments of deposition of sediments, which generally correspond to “Active Continental Margin” and “Oceanic and Continental Arc Islands”. In addition, it could be shown that sedimentary debris which contributed to the Puncoviscana basin, essentially correspond to siliceous sediments and igneous felsic, which are typical of Upper Continental Crust (UCC), being very similar sedimentary processes in all the studied samples, as evidenced by the overall chemical composition and behavior of the Rare Earth Elements.