Abstract

PINAN-LLAMAS, Aránzazu  and  ESCAMILLA-CASAS, José C.. Provenance and tectonic setting of Neoproterozoic to Early Cambrian metasedimentary rocks from the Cordillera Oriental and Eastern Sierras Pampeanas, NW Argentina. Bol. Soc. Geol. Mex [online]. 2013, vol.65, n.2, pp.373-395. ISSN 1405-3322.

Major, trace, and rare-earth element data for the Neoproterozoic to early Cambrian Puncoviscana Formation and related higher-grade metasedimentary rocks in Eastern Sierras Pampeanas, NW Argentina, were analyzed to evaluate their provenance, weathering, and tectonic setting during the upper Neoproterozoic-lower Paleozoic. The studied rocks are metapelites and metapsammites that were mainly affected by the lower Cambrian Pampean orogeny. Geochemical analyses indicate that the Puncoviscana Fm. and related rocks are characterized by moderate Chemical Index of Alteration (CIA) values. REE element distributions, Eu/Eu* values, and high Zr/Sc and Th/Sc ratios indicate that the samples were likely derived from predominantly upper-crust felsic sources. Tectonic discrimination diagrams based on immobile trace elements (e.g. Th-La-Sc, Sc-Th-Zr/10), multi-element patterns, REE characteristics, and diagnostic trace element ratios (i.e. Th/Sc, Zr/Hf, La/Th, La/Sc) imply that the tectonic setting of the source area was a continental island arc and/or an active continental margin. Geochemical signatures of low-grade metapsammitic samples (high Hf and Zr content, and high Zr/Sc ratios) indicate crustal recycling. The geometry and sequence of structures and microstructures preserved in all samples are pervasive and suggest a common and uniform deformational history during the Pampean orogeny. Geochemical signatures and structures of the studied samples are consistent with protolithic sediments of the Puncoviscana Fm. and related rocks initially deposited in an arc-related basin that was subsequently deformed during the Pampean orogeny.

Keywords : Geochemistry; metasedimentary rocks; provenance; Pampean orogeny; Puncoviscana Formation.

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