Resumo

CISTERNA, Clara Eugenia; COIRA, Beatriz  e  KOUKHARSKY, Magdalena. Tremadoc and Arenig volcano-sedimentary successions in the Sierra de Las Planchadas, Narváez: Evolutive records of the Famatinian magmatic arc. Rev. Asoc. Geol. Argent. [online]. 2010, vol.66, n.1-2, pp.180-193. ISSN 0004-4822.

Volcano-sedimentary Ordovician sections from the north of the Sistema de Famatina are analyzed, contributing with new petrological data to the understanding of the nature of magmas and associated volcanic processes related to the evolution of the magmatic arc in the region. Previous paleontological information, supported by structural studies and contact relationships with a granodiorite dated in 485 ± 7 Ma, assigned to these sedimentary rocks of Las Angosturas an early Tremadoc age, as well as an early to middle Arenig age to those of the Vuelta de Las Tolas - Chaschuil and Quebrada Larga - Punta Pétrea sections. The lithotypes that integrate the Tremadoc successions are basaltic, andesitic, dacitic and rhyodacitic lavas, interfingered with massive and laminated siltstones and fine psammites, with superimposed deformation and important hydrothermal alteration, as well as low grade and contact metamorphism. The Arenig deposits, folded and affected by well developed cleavage in some sectors, consist on basaltic, andesitic, dacitic and rhyolitic lavas, associated to hyaloclastic facies, syn-eruptive re-sedimented deposits and volcanogenic sedimentary facies. Despite both associations are subalkaline and peraluminous, for the early Tremadoc terms it is concluded that geochemical characteristics are compatible with an environment where melts from a depleted mantle (MORB) were produced, and enriched during subduction events. All these characteristics can be related to a marginal basin evolution. The Arenig volcanic rocks instead display a clear continental magmatic arc filiation. Both associations have similar characteristics to those observed in the western Puna region, which makes it probable to extend the magmatic arc recognized in the Sistema de Famatina within the Puna during Ordovician times.

Palavras-chave : Volcanism; Tremadoc; Arenig; Sierra de Narváez; Las Planchadas; Sistema de Famatina; Argentina.

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