Provenance analysis and tectonic setting of late Neoproterozoic metasedimentary successions in NW Argentina

摘要

Major, trace, and rare-earth element data for Puncoviscana Formation metasediments were used to constrain their provenance and tectonic setting. This unit, which crops out in northwest Argentina, consists mainly of pelite-greywacke turbidite sequences. Incipient regional metamorphism and a polyphase deformation, with a main deformation during the latest Proterozoic-earliest Cambrian Braziliano orogeny, affected the sedimentary sequences. The enrichment in light rare-earth and other incompatible trace elements over compatible ones, as well as the high and uniform Th/Sc ratios, indicate a predominance of upper-crust acid rocks as parental material. Some chemical characteristics of these rocks, such as their high Th/U, Rb/Sr, and Zr/Sc ratios, imply sedimentary recycling. On the basis of tectonic discriminant diagrams that employ trace elements considered relatively immobile during low-grade metamorphism, a passive margin setting can be inferred. Moreover, the comparison of the trace element contents of Puncoviscana metapelites with those of mudstones deposited in known tectonic settings shows the closest matching with passive margin shales.