Provenance and reconstruction of the tectonic setting in the Famatinian belt - Geochemistry of the late Cambrian – early Ordovician metasedimentary units of the Famatina system, Sierras Pampeanas, Argentina

Abstract

In order to evaluate depositional environment, provenance and tectonic setting, 19 samples of the metasedimentary rocks of the late Cambrian – early Tremadocian from the north of the Sierra de Narv´aez, developed at the upper-crustal section of the Famatinian Orogen, together with units of the same ages present at the central portion of the Famatina System (s.l.), the Volcancito and Bordo Atravesado Formations, were petrographic and geochemical analyzed.Although the analyzed metasedimentary rocks were affected by a low grade metamorphic event and locally by thermal metamorphism, the relatively uniform pattern of the REE and trace-element concentrations for the different samples attest nearly isochemical processes related to the metamorphic events, without significant remobilization.The metasandstone from the Sierra de Narv´aez, with abundance of quartz, feldspar and mainly volcanic fragments, are comparable with those related to a signature of magmatic arc influence. The plagioclase and the typical volcanic quartz point to the dominated volcanic inputs.Taking into account geochemical data, the metasedimentary successions (metapsammite and metapelite) display similar characteristics to those from recent deep-sea turbidite developed in continental arc margins. The presence of black shales facies in the succession, record deepening of the depositional environment due to an overall sea-level rise, denoting an oxygen depletion characteristic of them. The remarkable involvement of volcanic components in the north of the Sierra de Narv´aez deposits, interbedded as riodacitic to basaltic effusions and as lithic clastic components with the same nature in the metasandstone, allow to indicate that they representthe beginning of the volcanic activity along the Famatina System (s.l.), under the tectonic regime of a continental island arc.